233 pubblicazioni classificate nel seguente modo:

Surface reorientation induced by short light pulses in doped liquid crystals
OPTICS LETTERS
Autore/i: Lucchetti, Liana; D., Fedorenko; Francescangeli, Oriano; Y., Reznikov; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: Fast surface reorientation induced by a single 4-ns low-energy laser pulse in dye-doped liquid crystals is reported. The reorientation is due to light-induced modification of the surface anisotropy, which affects the liquid crystal's director through the appearance of a preferred direction on the irradiated surface. The detected signals can be interpreted as being the result of light-induced desorption and adsorption of dye molecules.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51487

Induction of mesomorphism through supramolecular association in coordination Pd(II) compounds of dialkyl 2,2’-bipyridine-4-4’-dicarboxylates
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: D., Pucci; G., Barberio; A., Crispini; M., Ghedini; Francescangeli, Oriano
Editore: TAYLOR & FRANCIS LTD, 4 PARK SQUARE, MILTON PARK, ABINGDON, ENGLAND, OXON, OX14 4RN
Classificazione: 1 Contributo su Rivista
Abstract: A series of three 4,4'-disubstituted-2,2'-bipyridines and the corresponding mononuclear cis-dichloro palladium(II) complexes have been synthesized. None of the ligands show mesomorphism. Upon their complexation to Pd(II) the peculiar structural arrangement characterized by intermolecular associations of the new derivatives induces mesogenic properties, confirming the new and exciting role of the coordination chemistry in metal-mediated formation of liquid crystals.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29773

Banana-shaped 1,2,4-oxadiazoles
PRAMANA-JOURNAL OF PHYSICS
Autore/i: S. I., Torgova; T. A., Geivandova; Francescangeli, Oriano; A., Strigazzi
Editore: Indian Academy of Sciences:CV Raman Avenue PO Box 8005, Bangalore 560080 India:011 91 80 3342546, EMAIL: office@ias.ernet.in, INTERNET: http://www.ias.ernet.in, Fax: 011 91 80 3346094
Classificazione: 1 Contributo su Rivista
Abstract: 3,5-Disubstituted 1,2,4-oxadiazoles are a new type of liquid crystalline (LC) compounds with asymmetrical five-membered heterocycle as a central unit. They have a bent shape and are very convenient model-compounds for studying the dependence of the LC properties on the molecular design. We have also synthesized and investigated 'banana-shaped' 1,2,4-oxadiazoles using the ester groups as the linkage units. The new compounds exhibit spontaneous polarization in the smectic phase, even if there is no chiral group in the molecules. Preliminary experimental data suggest the presence of spontaneous polarization in the nematic phase as well. In order to study the structural properties of the LC phases, X-ray diffraction (XRD) measurements on powder samples have been carried out. Based on the XRD data, a model of the structural arrangement of the bent molecules in the smectic phase is provided, which accounts for the macroscopic spontaneous polarization as well as the ferroelectric switching behavior.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29775

Liquid Crystal Ordering by Freezing of Thermal Convection Motion in Polymer Dispersed Liquid Crystals
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Lucchetta, Daniele Eugenio; Francescangeli, Oriano; Lucchetti, Liana; Simoni, Francesco
Editore: Gordon & Breach Science Publishers:PO Box 90, Reading RG1 8JL United Kingdom:011 44 118 9520303, 011 44 118 9560080, 011 44 181 9560080, EMAIL: philip.bott@gbmis.gbhap.com, INTERNET: http://www.gbhap.com/pubdate, Fax: 011 44 118 9568211
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/27413

Dye-doped liquid crystals as materials for optical information processing
Recent Research Developments in Materials Science
Autore/i: Francescangeli, Oriano
Editore: Research Signpost
Luogo di pubblicazione: TRIVANDRUM
Classificazione: 2 Contributo in Volume
Abstract: Invited Article
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/38342

Liquid crystal ordering by freezing of thermal convective motion in Polymer Dispersed Liquid Crystals
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Lucchetta, Daniele Eugenio; Francescangeli, Oriano; Lucchetti, Liana; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: This paper reports on the first observation of thermal convective motion in high-intensity photocured PDLC mixtures and demonstrates the possibility of LC ordering through the freezing of this thermal convective motion. The dependence of laser-cured PDLC films morphology on curing parameters such as light intensity, curing time, and sample temperature have also been studied. It is shown that the transition between ordered columnar and disordered turbulent motion is possible by increasing the laser beam intensity and that the flow patterns associated with both these regimes can be frozen by the photopolymerization process.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50761

Light-induced adsorption and desorption in dynamic and stable grating formation in methyl-red doped liquid crystals
JOURNAL OF NONLINEAR OPTICAL PHYSICS AND MATERIALS
Autore/i: Lucchetti, Liana; M., DI FABRIZIO; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: A detailed study of the light-induced gratings in Methyl-Red-doped 4-n-pentyl-4'-cyanobiphenyl (5CB) homeotropically aligned is reported. In particular, the dependence of diffraction efficiency upon the pump and probe polarizations has been investigated both for transient and permanent gratings. Our results confirm the earlier observations on the role of light-induced adsorption of MR molecules on the cell boundaries and demonstrate the common origin of the supranonlinear response and the permanent recording effect.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/27409

Chitosans depolymerized with the aid of papain and stabilized as glycosylamines
CARBOHYDRATE POLYMERS
Autore/i: Muzzarelli, Riccardo; Terbojevich, M.; Muzzarelli, C.; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: The viscosity of chitosan lactate solutions in the concentration range of interest for practical applications (120-150 g kg-1) was promptly lowered in the presence of papain at pH 3.2 and 25-40 °C. Thermal drying of partially depolymerized chitosan lactate brought about side reactions involving structure alterations, and yielded slightly soluble brilliant brown powders. Full solubility and improved organoleptic properties of the partially depolymerized chitosans were obtained by working up the solutions in such a way as to prevent reactions between the reducing ends and the amino groups, i.e. by incubating the ammonia-precipitated partially depolymerized chitosans at 60 °C under pressure with NH3 and drying at 40 °C. The pale yellow product (low molecular weight chitosan in glycosylamine form) had long shelf life and was promptly soluble in the presence of glycolic, lactic, ascorbic and hydrochloric acid, less promptly with citric acid. Three commercially available low molecular weight chitosans were also examined for comparison.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52689

Enhanced Nolinear Optical Response of Liquid Crystals
NONLINEAR OPTICS for the INFORMATION SOCIETY
Autore/i: Simoni, Francesco; Francescangeli, Oriano; Lucchetta, Daniele Eugenio; Lucchetti, Liana
Editore: Kluwer Academic Pub
Luogo di pubblicazione: Dordrecht
Classificazione: 2 Contributo in Volume
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72427

Light-induced anchoring and reorientation effects in dye-doped liquid crystals
Liquid Crystals VI
Autore/i: Francescangeli, Oriano; Lucchetti, Liana; Simoni, Francesco; S., Slussarenko; E., Ouskova; Y., Reznikov; S., Shiyanovskii; J. L., West
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: A review of the recent results of our group in the field of light-induced anchoring and reorientation effects in dye-doped liquid crystals (LCs) is presented. In particular, the phenomena of photoinduced anchoring and permanent reorientation over a polymeric boundary surface of a dye-doped LC cell is reported, both in the isotropic phase and in the orientationally ordered nematic phase. The results have been interpreted microscopically in terms of adsorption and desorption of the dichroic azo-dye (methyl-red) molecules onto the illuminated surface during light irradiation. The model proposed is in agreement with recent results on the dynamic and stable grating formation in methyl-red doped LCs.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52513

SINE: surface induced nonlinear effects
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Lucchetti, Liana; Lucchetta, Daniele Eugenio; Francescangeli, Oriano; Simoni, Francesco
Editore: Gordon & Breach Science Publishers:PO Box 90, Reading RG1 8JL United Kingdom:011 44 118 9520303, 011 44 118 9560080, 011 44 181 9560080, EMAIL: philip.bott@gbmis.gbhap.com, INTERNET: http://www.gbhap.com/pubdate, Fax: 011 44 118 9568211
Classificazione: 1 Contributo su Rivista
Abstract: Pump-probe and TIR experiments have been performed on the dye-doped nematic liquid crystal 5CB, in order to study the basic mechanisms of the extraordinarily large nonlinear response recently reported. Experimental data show that light-induced modifications of the anchoring conditions can be the origin of the observed effect. The bulk reorientation due to the collective elastic behaviour of the liquid crystal gives then rise to the nonlinearity, which occurs without a direct optical torque on the molecular director in the bulk. We have called this effect SINE (Surface Induced Nonlinear Effect).
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50997

Ordering and director field configuration in single droplets of liquid crystals probed by X-ray microdiffraction
EUROPHYSICS LETTERS
Autore/i: Francescangeli, Oriano; C., Ferrero; Lucchetti, Liana; Simoni, Francesco; M., Burghammer
Classificazione: 1 Contributo su Rivista
Abstract: X-ray microdiffraction (μ-XRD) is used for the first time to probe the liquid crystal (LC) ordering in confined LCs. We report on the direct observation of the director field in single droplets of nematic LCs embedded in a solid polymeric matrix (polymer-dispersed LCs). The bipolar configuration is identified in droplets with radius R ≤ 1 μm. Both the director distribution function and the droplet order parameter are obtained from diffraction patterns and the results are in excellent agreement with theoretical calculations. This technique is unique in its application to dispersed mesophases in that it allows to probe the local (μm length scale) LC ordering. The possibility of focusing measurements on single droplets eliminates the problems connected with averaging, which are typical of other techniques. Our results prove that μ-XRD is a novel and valuable tool in the study of confined LCs and open new exciting opportunities for future investigations.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52995

EXAFS Study of the Liquid Crystalline Phase of the Cyclopalladated 4-4'-bis(hexyloxy)azoxybenzene Acetylacetonate Complex
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Francescangeli, Oriano; C., Ferrero; D., Pucci; M., Ghedini
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: An EXAFS study of the mononuclear nematogenic cyclopalladated 4,4′-bis(hexyloxy)azoxybenzene complex in its liquid-crystalline phase is reported, aimed at exploring the metal coordination environment and confirming either the nature of intermolecular correlations or the presence of polar multimers. The interatomic distances between the palladium center and the atoms of the first coordination shell have been determined with an accuracy better than 10-2 A. The results of the data analysis also indicate that the intermolecular interactions, if any, are very weak and do not involve the palladium(II) coordination sphere. In addition, they suggest that the aggregation model previously proposed to account for the ferroelectric behavior of this compound has to be revised to consider the possibility of either van der Waals and/or polar intermolecular interactions or a peculiar packing mode imposed by the P-shaped molecular geometry.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29553

Crystal architecture and mesophase structure of long-chain N-alkylpyridinium tetrachlorometallates
INORGANICA CHIMICA ACTA
Autore/i: F., Neve; Francescangeli, Oriano; A., Crispini
Editore: Elsevier BV:PO Box 211, 1000 AE Amsterdam Netherlands:011 31 20 4853757, 011 31 20 4853642, 011 31 20 4853641, EMAIL: nlinfo-f@elsevier.nl, INTERNET: http://www.elsevier.nl, Fax: 011 31 20 4853598 Editore precedente:Prof Ugo Croatto Luogo pubbl. Padova Ultimo luogo pubblicazione: Lausanne.
Classificazione: 1 Contributo su Rivista
Abstract: The N-hexadecylpyridinium derivatives [C16-Py]2[MCl4] (M=Cd (1), Zn (2)) were prepared and structurally characterized by X-ray diffraction methods. The crystal structure of 1 reveals a layered arrangement with alternation of monolayers of interdigitated cations with layers of isolated [CdCl4]2- anions. C-H⋯Cl-Cd interactions reinforce the association between anions and cations in the polar region of the supramolecular structure. Both 1 and 2 display a thermotropic smectic A phase in addition to some high-temperature crystalline modifications. The thermal polymorphism of the salts was studied by X-ray powder diffraction, differential scanning calorimetry (DSC), and thermal optical microscopy. The structural and mesomorphic characteristics of 1 and 2 are compared with those of the analogous salts along the series [C16-Py]2[MCl4] (M=Co, Ni, kCu, Zn, Pd, Cd).
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29554

Hidden Photoalignment of Liquid Crystals in Isotropic Phase
PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Autore/i: Simoni, Francesco; Fedorenko, D.; Reznikov, Yu; Shiyanovskii, S.; Francescangeli, Oriano; West, L.
Editore: American Institute of Physics:2 Huntington Quadrangle, Suite 1NO1:Melville, NY 11747:(800)344-6902, (631)576-2287, EMAIL: subs@aip.org, INTERNET: http://www.aip.org, Fax: (516)349-9704
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/27132

Photoorientation of Liquid Crystals due to Light Induced Desorption/Adsorption of Dye Molecules on Aligning Surface
PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Autore/i: E., Ouskova; Reznikov, Y. u.; S. V., Shiyanovskii; L., Su; J. L., West; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72428

Morphological and electro-optical properties of polymer dispersed liquid crystals cured by high intensity laser radiation
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Lucchetta, Daniele Eugenio; Francescangeli, Oriano; Lucchetti, Liana; L., Gobbi; Simoni, Francesco
Editore: Gordon & Breach Science Publishers:PO Box 90, Reading RG1 8JL United Kingdom:011 44 118 9520303, 011 44 118 9560080, 011 44 181 9560080, EMAIL: philip.bott@gbmis.gbhap.com, INTERNET: http://www.gbhap.com/pubdate, Fax: 011 44 118 9568211
Classificazione: 1 Contributo su Rivista
Abstract: We have studied the morphology and the electrooptical properties of Polymer Dispersed Liquid Crystals prepared by the Polymer Induced Phase Separation technique under high-intensity UV laser curing. Photoinduced thermal convective motions have been observed in the directly illuminated area, which originates unusual morphological patterns consisting of ordered and/or disordered structures, depending on the curing intensity. We show that transition between ordered (columnar) and disordered (turbulent) motion is possible by increasing the laser beam intensity and the flow patterns associated to both these regimes can be frozen in by the photo-polymerization process. We show also that localized high-intensity curing generates a gradient of the droplet-size distribution outside the directly irradiated area essentially due to the non-uniform spatial-distribution of scattered intensity. This complex morphology reflects into a peculiar electrooptical behavior that could find potential application in new optical devices.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/27138

Photo-orientation of liquid crystals due to light-induced desorption and adsorption of dye molecules on an aligning surface
PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Autore/i: E., Ouskova; Reznikov, Y. U.; S. V., Shiyanovskii; L., Su; J. L., West; O. V., Kuksenok; Francescangeli, Oriano; Simoni, Francesco
Editore: pubblicata da: AMERICAN PHYSICAL SOC, ONE PHYSICS ELLIPSE, COLLEGE PK, USA, MD, 20740-3844
Classificazione: 1 Contributo su Rivista
Abstract: We show that adsorption of dye molecules control the light-induced alignment of dye-doped nematic liquid crystal (LC) on a nonphotosensitive polymer surface. The dependencies of light-induced twist structures on exposure, thermal baking, thickness, and aging before irradiation of the LC cells allowed us to propose the following mechanism for the alignment. Before irradiation, the "dark"-adsorbed layer on the tested surface is formed from dye molecules predominantly aligned along the initial direction of the director. Irradiation of the cell with linearly polarized light produces an additional layer with different orientational ordering of dye molecules. The final easy axis is determined by the competition of "dark" and light-induced contributions to anchoring and is aligned between the "dark" easy axes and polarization of the light. For quantitative interpretation, we apply the tensor model of anchoring and assume that the photoalignment in the mesophase is a cumulative effect of the light-induced anchoring on the background of the already existing anisotropic "dark" dye layer.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/31192

Droplet-size distribution gradient induced by laser curing in polymer dispersed liquid crystals
LIQUID CRYSTALS
Autore/i: Lucchetta, Daniele Eugenio; Francescangeli, Oriano; Lucchetti, Liana; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We have studied the morphology and electro-optical properties of polymer dispersed liquid crystals prepared by polymerization-induced phase separation (PIPS) under high intensity UV laser curing. The results have shown that localized high intensity curing generates a gradient of the droplet size distribution outside the directly irradiated area as a consequence of the non-uniform spatial distribution of the scattered intensity. Such a distribution of the droplet size reflects in a peculiar electro-optical behaviour that could find potential application in optical devices. Both shape and spatial extent of the droplet size gradient are affected by the spatial velocity of polymerization which in turn strongly depends on the intensity of the curing laser beam. This dependence has also been experimentally investigated.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50976

On the origin of the huge nonlinear response of dye-doped liquid crystal
OPTICS EXPRESS
Autore/i: Simoni, Francesco; Lucchetti, Liana; Lucchetta, Daniele Eugenio; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: We report the results of an investigation carried on Methyl Red-doped nematic liquid crystals with the aim of studying the basic mechanism of the extraordinarily large nonlinear response recently reported. We show that the experimental data can be explained as due to light-induced modifications of the anchoring conditions leading to director reorientation on the irradiated surface, which in turn gives rise to a bulk reorientation through the cell. We have called this phenomenon SINE (Surface Induced Nonlinear Effect) to remind that it occurs "without" (= sine in latin language) a direct optical or electric torque on the director in the bulk.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51304

Enhanced Nonlinear Optical Response of Liquid Crystals
Nonlinear Optics for the Information Society
Autore/i: Simoni, Francesco; Francescangeli, Oriano; Lucchetta, Daniele Eugenio; Lucchetti, Liana
Editore: Kluwer Academic Publishers
Luogo di pubblicazione: DORDRECHT
Classificazione: 2 Contributo in Volume
Abstract: Invited Article
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50423

Light-Controlled Anchoring Energy in Nematic Liquid Crystals
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Francescangeli, Oriano; Lucchetta, Daniele Eugenio; Y., Reznikov; S., Slussarenko; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: In this paper we show the possibility of regulating the dose of the anchoring energy under the control of the incident light. Using a dye-doped nematic sample where it was previously demonstrated the effect of light-induced anchoring, we measured the threshold for the Fredericksz transition for different irradiation times using a low power laser beam. Our data compare favourably to the existing theory and show that the amount of induced anchoring energy increases linearly with the irradiation time.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51323

Hidden photoalignment of liquid crystals in the isotropic phase
PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Autore/i: E., Ouskova; D., Fedorenko; Reznikov, Y. U.; S. V., Shiyanovskii; L., Su; J. L., West; O. V., Kuksenok; Francescangeli, Oriano; Simoni, Francesco
Editore: pubblicata da: AMERICAN PHYSICAL SOC, ONE PHYSICS ELLIPSE, COLLEGE PK, USA, MD, 20740-3844
Classificazione: 1 Contributo su Rivista
Abstract: We found the effect of a hidden photoalignment of a dye-doped nematic liquid crystal (LC) on a nonphotosensitive polymer surface after polarized irradiation of the cell in the isotropic phase. We observed that irradiation resulted in a uniform planar orientation of the LC after cooling to the mesophase. The direction of a light-induced easy axis on the polymer can he either parallel or perpendicular to the polarization of the incident light, depending on the light intensity. We attribute this behavior to two mechanisms of photoalignment: light-induced adsorption of dye molecules on the substrate, and anisotropic desorption in a previously adsorbed dye layer. The experimental results on photoalignment of a LC on a thin dye film confirm our model.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/31185

Properties of bulk-mediated photoalignment of doped liquid crystal
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: D., Fedorenko; Francescangeli, Oriano; E., Ouskova; V., Reshetnyak; Y., Reznikov; Simoni, Francesco; S., Shiyanovskii
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: We have found that producing a light-induced easy axis in a liquid crystal cell doped with methyl red can result in surface director reorientation both toward and outward the polarization of the incident light. This pointed out two different mechanisms of light-induced anchoring in the system. We proposed that these mechanisms are light-induced anisotropy in the adsorbed MR-layer and light-induced adsorption of MR molecules on the substrate. The study of light-induced anchoring in the isotropic phase showed that the mechanism of light-induced anisotropy in adsorbed MR-layer prevails at small light intensities, whereas the mechanisms of light-induced adsorption dominates at high intensities.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/31186

Heteroligand Palladium Complexes with One or Two Chiral Centres
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: D., Pucci; Francescangeli, Oriano; M., Ghedini
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: A series of chiral mononuclear palladium(II) complexes, [(Az(n))Pd(L-m)], I-VIII, have been synthesized. Herein the Az(n)Pd fragments represent the cyclopalladated 4-tetradecyloxy-4'-alkoxyazobenzene bearing an optically active carbon atom in a terminal alkoxy chain while HLm is the anion arising from the achiral N-[4'(dodecyloxy)resorcylidene]-4-(alkyl)anilines or the N-[4'-(dodecyloxy) resorcylidene]-4-(alkoxy)anilines containing a stereogenic center in a lateral chain. The optically active alkoxy tails are derived by S-(-)-beta-citronellol and R-(-)-2-octanol. Thermotropic mesomorphism, namely nematic and smectic phases, has been observed for almost all the complexes, with higher thermal stability and clearing temperatures of the same order or lower than those of the corresponding organic ligands.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/31193

Optical Nonlinearities of Liquid Crystals Controlled by Surfaces
Spatial Light Modulators: Technology and Applications
Autore/i: Lucchetti, Liana; Lucchetta, Daniele Eugenio; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: We show that light-induced modification of the anchoring conditions can lead to an extraordinarily large optical response in dye-doped nematic liquid crystals. The bulk reorientation due to the collective elastic behavior of the liquid crystal is the origin of the nonlinearity, which occurs without a direct optical torque on the molecular director in the bulk. We call this effect SINE (Surface Induced Nonlinear Effect). These results can also explain the origin of the supranonlinear behavior recently observed in the same composites.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53287

A2[MX4] Copper(II) Pyridinium Salts. From Ionic Liquids to Layered Solids to Liquid Crystals
CHEMISTRY OF MATERIALS
Autore/i: F., Neve; Francescangeli, Oriano; A., Crispini; J., Charmant
Editore: American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671
Classificazione: 1 Contributo su Rivista
Abstract: The synthesis and characterization of a novel series of tetrachlorocuprate salts, based on N-alkylpyridinium cations ([Cn-Py](+)), are described. The [Cn-Py](2)[CuCl4] salts (n = 6, 9-18) were found to be crystalline solids except for the short-chain homologues (n = 6, 9, 10), which were obtained as viscous liquids. X-ray powder diffraction measurements showed that in the crystalline state the ionic species give rise to layered structures. An X-ray crystal structure study of [C15-Py](2)[CuCl4] also confirmed the lamellar packing and revealed the monolayer type of organization with strong interdigitation and canting of N-alkyl chains. Most solid salts (n greater than or equal to 12) are thermotropic liquid crystals, with hexagonal columnar, cubic, and smectic phases appearing in the order of increasing chain length and/or temperature. This unique phase behavior has been undoubtedly proved by optical, calorimetric, and diffractometric techniques. The details of the structural organization in both the columnar and cubic phases are not entirely defined yet.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/31188

Optical Properties of Polymer-dispersed Liquid Crystals
INTERNATIONAL JOURNAL OF POLYMERIC MATERIALS
Autore/i: Simoni, Francesco; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: Electrooptical properties of polymer-dispersed liquid crystals (LCs) are analyzed from the point of view of the order created by the electric field, dynamic changes of the order (orientation) parameter, and optical transmittivity. Optical phase retardation causes an optical phase shift and is related to thermal effects. Nonlinear optical properties are investigated from the point of view of self-transparency, nonlinear gratings, threshold degenerate wave mixing, optical bistability and second harmonic generation.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50334

Enhancement of the optical nonlinearity in liquid crystals throughout the photovoltaic effect
IQEC, International Quantum Electronics Conference Proceedings
Autore/i: Francescangeli, Oriano; Lucchetti, Liana; Simoni, Francesco; S., Slussarenko
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: The transient behavior of the photovoltaic effect detected in the same kind of cell using c.w. and pulsed light excitation was examined. The study was performed on sandwich-like cells consisting of two parallel plane indium tin oxide-coated glass substrates, filled with mixture of the nematic 5CB liquid crystal and a small amount of methyl red. Results demonstrated a change of polarity of the photoinduced electromotive force while reaching the steady-state value under c.w. irradiation; and the generation of a transient photovoltage induced by a single 4 ns laser pulse with moderate energy density.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53047

Structural Studies on Layered Alkylpyridinium Iodopalladate Networks
INORGANIC CHEMISTRY
Autore/i: F., Neve; A., Crispini; Francescangeli, Oriano
Editore: American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671
Classificazione: 1 Contributo su Rivista
Abstract: The reaction of alkylpyridinium (C(n)H(2n+1)NC5H5, hereafter Cn-Py) iodide salts in aqueous acetonitrile with a preformed palladium iodide precursor afforded two different types of organic-inorganic phases depending on the molar ratio. A 2:1 ratio yielded the phase [Cn-Py]2[PdI4] (3, n = 14, 16), which crystallized in the triclinic crystal system. The X-ray crystal structure of 3, (n = 14), refined in the space group P1 (a = 8.918(3) Å, b = 9.894(3) Å, c = 29.062(12) Å, α = 93.51(3)°, β = 94.17(3)°, γ = 115.60(3)°, and Z = 2), consists of interdigitated bilayers with a basal spacing of 29.0 Å. The aliphatic chains of the cations, which run almost parallel to the stacking direction, are fully stretched between polar planes built on isolated. [PdI4]2- anions and cation headgroups. Changing the organic cation to palladium ratio to 1:1 led to a new phase [Cn-Py]2[Pd2I6] (4, n = 14, 16), which crystallizes in the triclinic P1 space group (a = 9.399(4) Å, b = 14.264(6) Å, c = 29.415(13) Å, α = 92.11(4)°, β = 90-07(4)°, γ = 104.53(3)°, Z = 3 for 4(n = 14); a = 9.417(2) Å, b = 14.215(3) Å, c = 31.552(6) Å, α = 87.96(3)°, β = 87.63(3)°, γ = 75.67(3)°, Z = 3 for 4(n = 16)). The layered structure is basically of a continuously interdigitated single-layer type, with a bilayer sublattice superimposed. Isolated [Pd2I6]2- anions contribute to the inorganic planes. A high degree of interdigitation and tilting of the aliphatic chains lead to basal spacings of 29.4 and 31.5 Å for 4(n = 14) and 4(n = 16), respectively. The [Cn-Py]2[PdI4] and [Cn-Py]2[Pd2I6] phases were characterized by thermal analysis. Mesomorphic behavior was observed only for 3(n = 16), which was confirmed by variable-temperature powder XRD and optical microscopy.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29532

Dye-doped photorefractive liquid crystals for dynamic and storage holographic grating formation and spatial light modulation
PROCEEDINGS OF THE IEEE
Autore/i: I. C., Khoo; M., Shih; M. V., Wood; B. D., Guenther; P. H., Chen; Simoni, Francesco; S., Slussarenko; Francescangeli, Oriano; Lucchetti, Liana
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/45966

Dye-doped Photorefractive Liquid Crystals for Dynamic and Storage Holographic Grating Formation and Spatial Light Modulation
PROCEEDINGS OF THE IEEE
Autore/i: I. C., Khoo; M. Y., Shih; M. V., Wood; B. D., Guenther; P. H., Chen; Simoni, Francesco; S. S., Slussarenko; Francescangeli, Oriano; Lucchetti, Liana
Editore: IEEE / Institute of Electrical and Electronics Engineers Incorporated:445 Hoes Lane:Piscataway, NJ 08854:(800)701-4333, (732)981-0060, EMAIL: subscription-service@ieee.org, INTERNET: http://www.ieee.org, Fax: (732)981-9667
Classificazione: 1 Contributo su Rivista
Abstract: The basic mechanisms of photo-induced space charge field formation, director axis re-orientation, and refractive index changes in fullerene C60- and dye-doped nematic liquid crystals films are presented. In particular, in aligned methyl-red-doped nematic liquid crystal film, we observe a nonlinear index change coefficient as high as 10 cm2/W, associated with purely optically induced liquid crystal director axis re-orientation. Experimental observations of dynamic and high-resolution storage holographic grating formation, two beam coupling with gain of nearly 3000 cm-1, optical limiting action at nanowatt cw laser power, and incoherent-coherent image conversion at μW/cm2 light intensity level are discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29528

Synthesis, Mesomorphism, and Spectroscopic Characterization of Bis[4-(n-alkoxy)-5-(p-n-tetradecylphenylazo)]-Substituted(N,N’-Salicylidenediaminato)nickel(II) Complexes
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY
Autore/i: I., Aiello; M., Ghedini; M., LA DEDA; D., Pucci; Francescangeli, Oriano
Editore: Wiley-VCH Verlag GmBH:PO Box 101161, D 69451 Weinheim Germany:011 49 6201 606147, EMAIL: service@wiley-vch.de, INTERNET: http://www.wiley-vch.de, Fax: 011 49 6201 606328
Classificazione: 1 Contributo su Rivista
Abstract: The bis[4-(n-C(m)H(2m+1)O)-5-(p-C(14)H(29)C6H4N=N)]-substituted N,N'- salicylidenediamines H2[L(N)(m,14)] (N = 1: 1,2-diaminoethane; N = 2: 1,3- diaminopropane; N = 3: 1,3-diamino-2,2-dimethylpropane; m = 6 or 18) have been synthesized. Both the N = 2 and 3 series of compounds display a smectic C (SmC) mesophase, with clearing points well below 100 °C. By treating the H2[L(N)(m,14)] ligands with an Ni(II) salt, liquid crystalline mononuclear complexes with 'unconventional' (lateral-tailed) molecular shape form. These Ni[L(N)(m, 14)] complexes, showing nematic and smectic disordered phases, are stable over a quite large temperature range and have been characterized by different spectroscopic techniques. The newly synthesized mesogens exhibit lower transition temperatures and higher thermal stability than homologous complexes Ni[L(N)(14)] with a 'conventional' rod-like molecular geometry.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29529

Effects of light on the molecular orientation of liquid crystals
JOURNAL OF PHYSICS. CONDENSED MATTER
Autore/i: Simoni, Francesco; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: A review of basic physical phenomena underlying the light-induced molecular reorientation in nematic liquid crystals is presented. A detailed description of the mechanisms of direct optical torque, photoisomerization and photorefractivity and of their effect on the macroscopic order of liquid crystals is reported. The first part of the article deals with the study of reorientation effects in transparent liquid crystalline materials. Here, the effects of photo-induced molecular reorientation are fully interpreted within the framework of classical electrodynamics and standard continuum theory of liquid crystals. We investigate the peculiar properties related to the macroscopic anisotropy and the collective behaviour of liquid crystals that result in extraordinarily large nonlinear optical response. Afterwards, the behaviour of liquid crystals in the presence of light absorption is considered and the related reorientation effects are discussed. We give a review of the wide phenomenology which is met in liquid crystals when doped with absorbing azo-dye molecules. The photoisomerization process that in this case drives the evolution of the dye-liquid crystal mixture consequent to the interaction with the light is discussed in detail. Finally, the relatively new field of photorefractivity in liquid crystals as a source of molecular reorientation is considered. We describe the different mechanisms contributing to the creation of a space-charge field such as conductivity anisotropy, dielectric anisotropy and photocharge production. A theoretical discussion of the fundamental mechanisms regulating the dc-field-assisted optically induced space-charge fields and the optical molecular reorientation in nematic liquid crystal films is also given.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51188

High Resolution Polarization Holography and Optical Storage in Liquid Crystals
INFM HIGHLIGHTS 1996/1997
Autore/i: Simoni, Francesco; Francescangeli, Oriano; S., Slussarenko; Y., Reznikov
Classificazione: 5 Altro
Abstract: Invited Contribution
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/48274

Light-Induced Surface Sliding of the Nematic Director in Liquid Crystals
PHYSICAL REVIEW LETTERS
Autore/i: Francescangeli, Oriano; Slussarenko, S.; Simoni, Francesco; Andrienko, D.; Reznikov, Y.
Classificazione: 1 Contributo su Rivista
Abstract: We report the effect of light-induced sliding of the nematic director over an isotropic boundary surface in an azo-dye doped liquid-crystal cell. We show that illumination of the cell with polarized laser light induces transient dynamic sliding followed by permanent reorientation of the director. The two effects are in competition and tend to orient the director along mutually orthogonal directions. The sliding can be controlled and even completely quenched by the amount of induced anchoring energy. A physical model is proposed which accounts for the experimental results.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50928

Dinuclear Cyclopalladated Azobenzene Complexes: a Comparative Study on Model Compounds for Organometallic Liquid-Crystalline Materials
APPLIED ORGANOMETALLIC CHEMISTRY
Autore/i: M., Ghedini; D., Pucci; A., Crispini; I., Aiello; F., Barigelletti; A., Gessi; Francescangeli, Oriano
Editore: Attuale:CAMBRIDGE UNIV PRESS, 40 WEST 20TH ST, NEW YORK, USA, NY, 10011-4211 John Wiley & Sons Limited:1 Oldlands Way, Bognor Regis, P022 9SA United Kingdom:011 44 1243 779777, EMAIL: cs-journals@wiley.co.uk, INTERNET: http://www.wiley.co.uk, Fax: 011 44 1243 843232
Classificazione: 1 Contributo su Rivista
Abstract: The series of dinuclear 4,4′-bis(hexyloxy)azobenzene, [H(Azo-6)], cyclopalladated complexes of general formula [Azo-6)Pd(μ-X)]2, (X = Cl, Br, I, N3, SCN, OAc) and [Azo-6)2Pd2(μ-Ox)] (Ox = oxalate) have been synthesized and investigated for mesomorphism and spectroscopic properties. Single-crystal X-ray analysis of the dinuclear bromo- and iodo-bridged complexes has been performed. The structural data, compared with those of the known homologous chloro compound, show that all the [Azo-6)Pd(μ-X)]2)] (X = Cl, Br, I) molecules crystallize in the monoclinic space group P21/c and are isomorphous. They are arranged in slipped pairs with intermolecular non-bonding, Pd-Pd contacts ranging from 3.668(1) Å(X = Cl) to 3.758(3) Å(X = I). The different nature of the bridging group allows variation of the distance between the palladium atoms and the bond environment experienced by the metal centers. Thus, this comparative study reveals that the effectiveness of the bridging group in promoting thermotropic mesophases is greater for chloride, bromide, azide or oxalate than for iodide, thiocyanate or acetate. The greatest range of liquid-crystal behavior was displayed by [Azo-6)2Pd2(μ-Ox)]. Remarkably, this compound is the first example of a metallomesogen containing the bridging oxalate group. The bimetallic complexes exhibit different absorption spectra (i.e. colors) depending, in general terms, on the nature of the bridge connecting the two cyclometalated [H(Azo-6)] moieties, which can be varied so as to tune the optical properties. Blocking the azo group in the trans position results in several cases in weakly luminescent complexes, with luminescence efficiencies φ ≈10-4 and luminescence lifetimes of the order of nanoseconds. Using the data obtained from the 4,4′-bis(hexyloxy)azoxybenzene [H(Azoxy-6)] derivative, [Azoxy-6)Pd(μ-Cl)]2, from the mononuclear acetylacetonate (acac) complexes [(Azo-6)Pd(acac)] and [(Azoxy-6)Pd(acac)], and from the uncomplexed [H(Azo-6)] and [H(Azoxy-6)] ligands, the nature of the excited states relevant to the photophysical behavior are discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29525

Correlated columnar phases: aroylhydrazinato nickel (II) complexes as novel discotics
INORGANIC CHEMISTRY COMMUNICATIONS
Autore/i: A., Bacchi; M., Carcelli; Francescangeli, Oriano; F., Neve; P., Pelagatti; C., Pelizzi
Editore: Elsevier BV:PO Box 211, 1000 AE Amsterdam Netherlands:011 31 20 4853757, 011 31 20 4853642, 011 31 20 4853641, EMAIL: nlinfo-f@elsevier.nl, INTERNET: http://www.elsevier.nl, Fax: 011 31 20 4853598
Classificazione: 1 Contributo su Rivista
Abstract: A series of ligands derived from 2,3-butanedione and mono-, di- and tri-alkoxy substituted benzoylhydrazines is synthesised and characterised; they react with nickel(II) acetate giving Ni(ligand-2H) square planar complexes. The complex with six peripheral dodecyloxy side-chains exhibits a columnar (Colhd) mesophase; the X-ray structure of a model complex is also reported.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29524

Photoalignment effect induced by angular momentum of light in dye-doped liquid crystals
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: D., Andrienkoa; D., Fedorenko; Reznikov, Y. u.; S., Slussarenko; Francescangeli, Oriano; Simoni, Francesco
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: We studied the effective interaction of the angular momentum of light with a liquid crystal (LC) doped with azo-dye. The experiments were carried out in a combined cell with one substrate providing strong unidirectional planar alignment of LC and the other covered by isotropic polymer layer providing a degenerated planar alignment. The effect manifests itself as azimuth reorientation of the liquid crystal director under the action of circularly polarized light in the absorption band of azo-dye. The new orientation of LC was captured by the command surface because of a light-induced alignment memory effect. To describe the experimental dependencies we solved the self-consistent problem of the propagation of a circularly polarized light in the absorbing nonlinear media using the geometric optics approximation. Comparing the experimental data with numerical evaluation we obtain the basic parameters of the system: the orientation nonlinearly coefficient and the value of anchoring of the director with the polymer surface.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29526

Liquid Crystal Poly(glycidyl ether)s by Anionic Polymerization and Polymer-Analogous Reaction
POLYMER JOURNAL
Autore/i: M. C., Bignozzi; S. A., Angeloni; M., Laus; L., Incicco; Francescangeli, Oriano; D., Wolff; G., Galli; E., Chiellini
Editore: The Society of Polymer Science, Japan (SPSJ):Tsukiji Daisan Nagaoka Building, 2-4-2 Tsukiji Chuo-ku, Tokyo 03-3502-6471 Japan:011 81 3 35026471, Fax: 011 81 3 35932709
Classificazione: 1 Contributo su Rivista
Abstract: Two new series of liquid crystalline poly(glycidyl ether)s I and II containing a side-chain 4-alkoxy-azobenzene mesogenic unit were prepared according to two different synthetic routes. The former were prepared by ring-opening anionic polymerization of different mesogenic epoxides, while the latter were prepared by grafting the same mesogenic side chain onto preformed poly(epichlorohydrin) to different substitution extents. Poly(glycidyl ether)s I formed a sequence of different smectic mesophases and nematic mesophases, depending on the length of the alkoxy tail. For poly(glycidyl ether)s II the kind of the phase behavior (not liquid crystalline, nematic, nematic and smectic) was strongly correlated with the extent of mesogenic side-chain incorporation with greater degrees of substitution favoring the onset of more stable and ordered mesophases. No smectic monolayer arrangement was observed, but only bilayer smectic structures, either SA2 or SC2, were detected by X-ray diffraction investigations on powder or magnetically aligned samples.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29530

Structural Patterns in Polymer-Dispersed Liquid Crystal Films
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: S. J., Klosowicz; Francescangeli, Oriano; S., DI BELLA
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: Different methods for the creation of structural patterns in Polymer Dispersed Liquid Crystals (PDLC) are discussed and compared, with a special attention to the recent techniques of induced director pre-orientation and inhomogeneities creation in PDLC films. Examples of the periodic structural patterns obtained by means of different methods adopted during the PDLC preparation are reported. These PDLC with intrinsic structure patterns are very promising for the realization of both active and passive devices such as switchable light modulators, controlled diffraction gratings and switchable couplers for fiber optic systems.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29531

Mesomorphic 4'-functionalized 6'-phenyl-2,2'-bipyridines: tridentate ligands for organopalladium mesogens
LIQUID CRYSTALS
Autore/i: F., Neve; M., Ghedini; Francescangeli, Oriano; S., Campagna
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: A novel series of 6′-phenyl-2,2′-bipyridines (HL-n) substituted in the 4′ position with promesogenic functional groups has been prepared. The materials are strongly luminescent and display nematic mesomorphism. The HL-n behave as C,N,N-tridentate, cyclometallating ligands leading to [Pd(L-n)Cl] derivatives. Metal co-ordination promotes a considerable stabilization of the crystal phase, forcing mesophases to become metastable. All [Pd(L-n)Cl] species indeed exhibit a monotropic mesophase either nematic or smectic A in character depending on the chain length of the substituents on the central pyridine unit.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29519

Phase and Orientational Behaviors in Liquid Crystalline Main-Chain/Side-Group Block Copolymers
JOURNAL OF POLYMER SCIENCE. PART B, POLYMER PHYSICS
Autore/i: D., Ferri; D., Wolff; J., Springer; Francescangeli, Oriano; M., Laus; A. S., Angeloni; G., Galli; E., Chiellini
Editore: John Wiley & Sons Incorporated:Customer Service, 111 River Street:Hoboken, NJ 07030:(800)225-5945, (201)748-6000, EMAIL: societyinfo@wiley.com, INTERNET: http://www.wiley.com, Fax: (212)748-6551
Classificazione: 1 Contributo su Rivista
Abstract: The phase and orientational behaviors of a series of liquid crystalline (LC) AB-type diblock copolymers comprising thermotropic main-chain (MC) polyester and side-group (SG) polymethacrylate blocks were investigated by X-ray diffraction. The MC and SG blocks were phase separated and gave rise to their individual mesophases that coexisted at equilibrium. The samples were oriented by using either a magnetic field or a mechanical field. In magnetically aligned samples both the MC and SG microphases were oriented with their smectic planes orthogonal to the magnetic field direction, independent of the copolymer composition. Mechanically aligned, fiber samples showed different orientations of the MC and SG smectic planes for different sample compositions. In this case the disposition of the smectic planes of the MC and SG blocks was driven by the relative length of the two blocks. Some features of the X-ray patterns of the copolymers were compared to those of the MC and SG homopolymers. In addition, the MC smectic domains crystallized on annealing without affecting the orientation that had been achieved by applying a magnetic field.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29517

Light induced anchoring and memory effects in dye-doped liquid crystals
Liquid Crystals: Physics, Technology and Applications
Autore/i: Simoni, Francesco; Francescangeli, Oriano; I., Pepe; Y., Reznikov; S., Slussarenko
Editore: J. Rutkowska,S.J. Klosowicz,J. Zielinski,J. Zmija
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: We present a new type of effective photoregulation of the LC orientation on an aligning surface through light action upon the liquid crystal bulk. The illumination of an azo-containing LC bulk with polarized light is found to induce both stable (in time and temperature) high-resolution alignment onto the rigid surface and dynamic sliding of the director over the surface. Typical times of the director sliding over the aligning surface are of the order of 1 ms. Both effects are characterized by extremely small light intensities (as low as 10-1 J/cm2) and seem to be very promising for the development of optical devices for information processing and high density information storage. Light-induced surface memory effects are also observed in these systems as a consequence of induced anchoring of the molecular director. This technique has been applied to record both stationary and dynamic holograms with a spatial resolution of 7 μm. The surface memory effects have been applied to record both binary and gray scale images. As compared to other methods used in these materials the highest sensitivity and spatial resolution can be achieved: energy densities as low as 10-1 J/cm2 were sufficient to write gratings with a resolution better than 100 lines/mm.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/46320

Recording of permanent holographic gratings in liquid crystals
IEEE Nonlinear Optics: Materials, Fundamentals and Applications - Conference Proceedings
Autore/i: Simoni, Francesco; Francescangeli, Oriano; Lucchetti, Liana; S., Slussarenko; Y., Reznikov
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: A method is developed which is successful in exploiting binary image writing. By exploiting the high sensitivity of a medium, permanent recording are achieved by using a single pulse of the second harmonic of a Nd:YAG laser. The dye-doped liquid crystals are demonstrated to possess very interesting storage capabilities: no image degradation after more than one year, high spatial resolution, high sensitivity, and polarization sensitivity.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52799

X-ray investigation of new isomeric oxadiazoles
Liquid Crystals: Chemistry and Structure
Autore/i: Francescangeli, Oriano; L. A., Karamysheva; S. I., Torgova; A., Sparavigna; A., Strigazzi
Editore: J. Rutkowska,S.J. Klosowicz,J. Zielinski,J. Zmija
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: An X-ray investigation has been performed on five new 2,5-disubstituted 1,2,4-oxadiazoles with reversed structures containing 4-amylbiphenyl-, trans-4-amylcyclohexylphenyl- and 2-halophenyl-(hal = Cl, Br) as substituents. The aim was to confirm the data about the phase sequence, obtained via polarizing microscopy and differential scanning calorimetry, and to measure the structural parameters. Through X-ray diffraction technique, all substances showed only the nematic mesophase. Moreover, it was proved that some enthalpy variations previously attributed to crystal-crystal transitions are in fact due either to the rearrangement of the lattice or to the coalescence of the grains. However, for some substances, a second crystalline form C′ appeared at the melting point, on cooling from the isotropic phase. C′ turned out to be different from the starting form C1 of the sample, which had no any thermal cycle before.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/47220

Laser Beam Modulation Freezing on a Liquid Crystal Surface
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: D., Andrienko; Francescangeli, Oriano; E., Ouskova; Simoni, Francesco; S., Slussarenko; Y., Reznikov
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: We report the first observation of the formation of permanent light-induced annular patterns in a planar cell filled with dye-doped liquid crystal. The sample is placed between one rubbed surface, giving unidirectional planar alignment, and one isotropic surface, providing degenerated planar alignment. The patterns appear under the irradiation of the isotropic surface through the liquid crystal layer. The experimental results are explained in terms of spatial modulation of the light polarization over the isotropic surface, due to conformation nonlinearity of the mixture. The light-induced adsorption of azo-dye on the initially isotropic surface leads to "freezing" of this modulation and the appearance of a twisted director structure.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29522

Phase behavior and structural characterization of poly(1,3-propylene adipate)s with cyanoazobenzene side groups
LIQUID CRYSTALS
Autore/i: E. L., Tassi; M., Paci; P. L., Magagnini; B., Yang; Francescangeli, Oriano; F., Rustichelli
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The phase behaviour and the structure of three poly(1,3-propylene adipate)s containing cyanoazobenzene side groups bonded to the backbone unit through flexible spacers with 6, 8 and 10 methylene groups have been studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD) analysis. The polyadipates behave as enantiotropic side group liquid crystalline polymers. XRD analysis has shown that the organized phase of these polyadipates possesses a crystalline or a tilted structure of the SmF or SmG type. The temperature of fusion of this phase (Tm ≈ 45-48°C) is almost independent of the length of the side group spacers. The crystalline phase can be obtained only by prolonged annealing at room temperature because crystallization from the melt is kinetically hindered. The range of thermodynamic stability (Ti - Tm) of the mesophase formed on melting increases with the length of the side group flexible spacers. The structure of the mesophase, determined by XRD, is of the smectic A type, and is characterized by a relatively large longitudinal displacement of the side groups, which is responsible for the unusually weak low angle Bragg reflections.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29518

Synthesis, Structure, and Thermotropic Mesomorphism of Layered N-Alkylpyridinum Tetrahalopalladate(II) Salts
CHEMISTRY OF MATERIALS
Autore/i: F., Neve; A., Crispini; S., Armentano; Francescangeli, Oriano
Editore: American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671
Classificazione: 1 Contributo su Rivista
Abstract: Two homologous series of N-alkylpyridinium salts, [Cn-Py]2[PdX4] (n = 12, 14, 16, 18; X = Cl, Br), have been synthesized, and their thermal behavior has been studied by differential scanning calorimetry and hot-stage polarizing optical microscopy. Except for the substances with n = 12, all the materials show thermotropic polymorphism. The crystal structures of [C12-Py]2(PdCl4], [C16-Py]2[PdCl4, and [C16-Py]2[PdBr4] have been solved. All three complex salts crystallize in the triclinic space group P1. Crystal packing reveals layered structures with alternating polar and apolar sublayers, where each (PdX4)2- anion is sandwiched between two antiparallel pyridinium cations. Alkyl chains are highly interdigitated and tilted with respect to the layer normal. The structural characterization of the [Cn-Py]2- [PdX4] (n = 16, 18; X = Cl, Br) salts has been achieved also through variable-temperature powder X-ray diffraction. The [PdCl4]2- salts undergo transitions to a second crystalline phase and then to an ordered and a disordered smectic phase. The latter are assigned to single-layered smectic-E and partially bilayered smectic-Ad phases, respectively. On warming, the [PdBr4]2- analogues only show the smectic-Ad phase, preceded by a crystalline phase very similar to the room-temperature solid phase. The relative importance of hydrogen bonding throughout the sequence of structural changes is briefly addressed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29521

Hybrid nanocomposites based on polystyrene and a reactive organophilic clay
JOURNAL OF MATERIALS SCIENCE
Autore/i: M., Laus; M., Camerani; M., Lelli; K., Sparnacci; F., Sandrolini; Francescangeli, Oriano
Editore: Kluwer Academic Publishers:Journals Department, PO Box 322, 3300 AH Dordrecht Netherlands:011 31 78 6576050, EMAIL: frontoffice@wkap.nl, kluweronline@wkap.nl, INTERNET: http://www.kluwerlaw.com, Fax: 011 31 78 6576254
Classificazione: 1 Contributo su Rivista
Abstract: The preparation of new hybrid nanocomposites, by emulsion polymerization of styrene in the presence of a reactive organophilic clay, and their characterization are described. The reactive organophilic clay is synthesized by exchanging the inorganic cations in the interlayer structure of a natural clay with the quaternary salt of the aminomethylstyrene. This salt is prepared by a Gabriel reaction starting from the (chloromethyl)styrene. The polymeric matrix of the resulting materials was found to be constituted by polystyrene homopolymer and by a blocky copolymer of styrene and quaternary salt of the (aminomethyl)styrene units. The glass transition temperature of the nanocomposites increase as the percentage of organophilic clay increases, although the average molar masses of the polymeric matrix decrease, because of termination and/or chain-transfer reactions caused by the organophilic clay during the polymerization. Accordingly, the inherent reinforcing action due to the presence of the reactive organophilic clay is higher than the observed one.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29520

High resolution polarization gratings in liquid crystals
APPLIED PHYSICS LETTERS
Autore/i: S., Slussarenko; Francescangeli, Oriano; Simoni, Francesco; Y., Reznikov
Editore: American Institute of Physics:2 Huntington Quadrangle, Suite 1NO1:Melville, NY 11747:(800)344-6902, (631)576-2287, EMAIL: subs@aip.org, INTERNET: http://www.aip.org, Fax: (516)349-9704
Classificazione: 1 Contributo su Rivista
Abstract: Efficient recording of polarization gratings in dye-doped liquid crystals is reported. By exploiting the effect of light-induced anchoring of the molecular director, it has been possible to write stable holographic gratings with a diffraction efficiency of 8% at a resolution of 1000 lines/mm. The required surface energy density of 0.3 J/cm(2) sets these materials among the most sensitive for optical storage.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29670

High-pressure mesomorphic behavior of a chiral polyacrylate by X-ray diffraction in situ.
PHYSICAL REVIEW E
Autore/i: Francescangeli, Oriano; C., Ferrero; M., Lorenzen; P., Bösecke; B., Paci; Caciuffo, ROBERTO GIOVANNI MARIA
Classificazione: 1 Contributo su Rivista
Abstract: he high-pressure mesomorphic behavior of a chiral liquid crystalline polyacrylate has been studied by x-ray diffraction in situ. The results show the existence of monolayer smectic-A* and bilayer smectic-C* mesophases that coexist in the thermally untreated sample over a well-defined range of temperatures, from ambient pressure up to 133 MPa. Hydrostatic pressures of the order of 100-220 MPa are found to affect strongly the polymorphic behavior of the sample. The smectic-A* mesophase, which at ambient pressure coexists with an interdigitated smectic-C* structure, is stabilized over a temperature range which increases with pressure, whereas the formation of the smectic-C* phase is inhibited above 220 MPa. The pressure increment is found to introduce static positional disorder, and to reduce the long-range positional order in the smectic structure strongly. A transition sequence from the isotropic melt through the smectic-A* phase to a new crystalline structure is found by cooling isobarically down to room temperature. The proposed pressure-temperature phase diagram suggests the occurrence of peculiar disorder-order-disorder transitions as pressure is reduced isothermally.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52253

The effects of hydrogen bonding on the liquid crystalline behavior of semiflexible poly(urethane-ester)s
MACROMOLECULAR SYMPOSIA
Autore/i: M., Laus; A. S., Angeloni; Francescangeli, Oriano; G., Galli; E., Chiellini
Editore: Huethig & Wepf Verlag:Auf dem Wolf 4, CH 4018 Basel Switzerland:011 41 61 3179410, Fax: 011 41 61 3179411
Classificazione: 1 Contributo su Rivista
Abstract: The peculiar liquid crystalline behavior of two poly(urethane-ester)s TDI-C6C4 and TDI-C6C8 is reported. Evidence is provided of the formation of two nematic mesophases, a cybotactic nematic and a conventional nematic mesophase, in TDI-C6C8 and of one cybotactic nematic mesophase in TDI-C6C4. IR spectroscopy indicates that different hydrogen bonded and non-bonded structures occur with varying temperature. The transition from the nematic cybotactic mesophase to the nematic mesophase, or to the isotropic phase, is accompanied by a substantial decrease of the strength of the hydrogen bonds. This is also reflected in the dynamic mechanical behavior of these poly(urethane-ester)s which is similar to the one of slightly crosslinked thermoreversible networks.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29596

Mesophase structure and alignment under different fields of liquid crystalline main- chain/side-group block copolymers
MACROMOLECULAR SYMPOSIA
Autore/i: G., Galli; E., Chiellini; Francescangeli, Oriano; D., Ferri; D., Wolff; J., Springer; M., Laus; A. S., Angeloni
Editore: Huethig & Wepf Verlag:Auf dem Wolf 4, CH 4018 Basel Switzerland:011 41 61 3179410, Fax: 011 41 61 3179411
Classificazione: 1 Contributo su Rivista
Abstract: Liquid crystalline block copolymers are new materials in which multiple molecular interactions can provide the driving force for complex phase behaviors and states of order. Block copolymers containing both liquid crystalline main-chain polyester and side-group polymethacrylate blocks were investigated. They phase separated in the liquid crystalline state and their individual mesophases coexisted. The copolymers responded very differently when either a mechanical or a magnetic field was used for alignment. In the fibers the orientations of the side-group and main-chain smectic planes with respect to the fiber axis depended critically on the block lengths and on their distinct tendencies to align, whereas under a magnetic field the mesogens aligned collectively with their long molecular axis parallel to the field, independent of the copolymer structure.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29598

Orientational order of p-n-alkoxybenzylidene-p'-fluoroanilines. X-ray diffraction and electro-optic response of the chiral (S)-p-2-methylbutyloxy derivative
LIQUID CRYSTALS
Autore/i: L., Calucci; Francescangeli, Oriano; G., Gandolfo; L., Komitov; C. A., Veracini
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: This work continues our study of the mesomorphic properties of the p-n-alkoxybenzylidene-p'-fluoroanilines. Previous studies have shown that the straight chain homologues, with the number of carbon atoms in the chain ranging from 4 to 8, form smectic phases. In this paper we describe H-2 NMR studies of the homologues with n = 4, 5 and 8 and the synthesis and properties of a chiral branched chain derivative, (S)-p-2-methylbutyloxybenzylidene-p'-fluoroaniline. This compound is not mesomorphic, but does show solid state polymorphism. From an optical, electro-optical, DSC and X-ray diffraction study we infer that the higher temperature crystalline form is a CrE phase.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29594

Dye-doped liquid crystals as high-resolution recording media
OPTICS LETTERS
Autore/i: Simoni, Francesco; Francescangeli, Oriano; Y., Reznikov; S., Slussarenko
Editore: Optical Society of America:2010 Massachusetts Avenue Northwest:Washington, DC 20036:(800)762-6960, (202)223-8130, EMAIL: custserv@osa.org, INTERNET: http://www.osa.org, Fax: (202)223-1096
Classificazione: 1 Contributo su Rivista
Abstract: Light-induced anchoring of the molecular director is reported to be an efficient method for writing permanent holographic gratings in dye-doped liquid crystals. We have achieved higher sensitivity and spatial resolution in these materials with other methods. An energy density as low as 10(-1) J/cm(2) was sufficient to write gratings with a resolution higher than 100 lines/mm.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29595

New hybrid nanocomposites based on an organophilic clay and poly(styrene-b-butadiene) copolymers
JOURNAL OF MATERIALS RESEARCH
Autore/i: M., Laus; Francescangeli, Oriano; F., Sandrolini
Editore: Materials Research Society:9800 McKnight Road, Suite 327:Pittsburgh, PA 15237:(412)367-3003, EMAIL: info@mrs.org, INTERNET: http://www.mrs.org, Fax: (412)367-4373
Classificazione: 1 Contributo su Rivista
Abstract: The preparation, by direct melt intercalation, and the properties of new hybrid organic-inorganic nanocomposites, consisting of a commercial sample of poly(styrene-b-butadiene) copolymer (SBS) and a commercial organophilic clay containing the dioctadecyl dimethyl ammonium salt are described. In addition, several mixtures between the same copolymer and an unfunctionalized clay were prepared and studied. XRD spectra showed a partial insertion of the SBS block copolymer segments in the interlayers of the organophilic clay, accompanied by a loss of correlation within the layers. The degree of insertion increased by annealing the nanocomposites at 120 degrees C for increasing time periods. No interaction between the polymer matrix and the unfunctionalized clay was found. The storage modulus value, in the plateau region between the glass transition processes of the polybutadiene and the polystyrene blocks, and the glass transition temperature of the polystyrene block domain increase as both the organophilic clay content and the annealing time increase. The glass transition process of the polybutadiene block domain is practically unaffected by the filler content and the annealing treatments, These data are most promising for upgrading the thermo-mechanical behavior and the application temperature window of the SBS thermoplastic elastomers through the preparation of nanocomposites employing suitably designed organophilic clays.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29600

Structure of the nematic mesophase with cybotactic groups in liquid-crystalline poly(urethane-ester)s
PHYSICAL REVIEW E
Autore/i: Francescangeli, Oriano; M., Laus; G., Galli
Editore: American Institute of Physics:2 Huntington Quadrangle, Suite 1NO1:Melville, NY 11747:(800)344-6902, (631)576-2287, EMAIL: subs@aip.org, INTERNET: http://www.aip.org, Fax: (516)349-9704
Classificazione: 1 Contributo su Rivista
Abstract: The results of a structural analysis by x-ray diffraction on fiber samples of the nematic mesophase with cybotactic groups of poly(urethane-ester) TDI-C2C6, TDI-C6C4, TDI-C6C6, TDI-C6C8, and TDI-C6C10 as prepared from various mesogenic alkylene di[4-(omega-hydroxyalkyloxy-4-oxybenzoyl)oxybenzoate]s (CmCn; m = 2 or 6 and n = 4, 6, 8, or 10) and 2,4-toluenediisocyanate (TDI) are reported. Evidence is provided for the existence of two different molecular orderings within the nematic phases with cybotactic groups, to which different internal degrees of correlation correspond. The average dimension of the cybotactic clusters along the director is comprised between similar to 260 and similar to 560 Angstrom, whereas the average dimension perpendicular to the director ranges from similar to 130 to similar to 270 Angstrom. Accordingly, the cybotactic clusters present an asymmetrical ellipsoidal-like shape. On the other hand, the correlation length within the nematic liquid crystal surrounding the cybotactic clusters and along the director is between 38 and 45 Angstrom. These values are of the order of the molecular length. These findings highlight the multidomain nature of the mesophase consisting of large and asymmetric clusters surrounded by a conventional nematic endowed with a very low correlation degree.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29593

On the peculiar macromolecular organization of nematic poly(urethane-ester)s
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Francescangeli, Oriano; M., Laus; G., Galli
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The peculiar mesophase structure of a series of thermotropic poly(urethane-ester)s is discussed. The polymers form different nematic phases, namely a nematic mesophase with cybotactic groups and a conventional nematic mesophase. The X-ray diffraction analysis suggests that two types of structural arrangements, namely smectic C-like and conventional nematic structures, coexist inside the cybotactic nematic mesophases, to which different internal degrees of correlation correspond. The correlation length parallel to the director of the nematic mesophase ranges from 38 to 45 Angstrom. In the cybotactic groups the correlation lengths parallel and perpendicular to the director range from 260 to 560 Angstrom and 130 to 270 Angstrom, respectively.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29599

Hybrid Liquid Crystalline Block Copolymers
Recent Anvances in Liquid Crystalline Polymers: Technological Advances
Autore/i: M., Laus; M. C., Bignozzi; A. S., Angeloni; G., Galli; E., Chiellini; Francescangeli, Oriano
Editore: Americam Chemical Society
Luogo di pubblicazione: WASHINGTON DC
Classificazione: 2 Contributo in Volume
Abstract: Invited Article
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/42288

Pressure-induced stabilization of the smectic A* phase in a chiral polyacrylate
EUROPHYSICS LETTERS
Autore/i: Caciuffo, ROBERTO GIOVANNI MARIA; Francescangeli, Oriano; Paci, B.; Bösecke, P.; Ferrero, C.; Lorenzen, M.
Classificazione: 1 Contributo su Rivista
Abstract: The pressure-temperature phase diagram of a chiral liquid crystal polyacrylate has been studied in situ by X-ray diffraction. Hydrostatic pressures of the order of 100-200 MPa strongly influence the polymorphic behaviour of the sample. The smectic A* mesophase, which at ambient pressure coexists with an interdigitated smectic C* structure, is stabilized over a temperature range which increases with pressure. The formation of the smectic C* phase is inhibited at 220 MPa and occurs only upon the first heating process at 133 MPa. A transition sequence from the isotropic melt through the smectic A* phase to a new crystalline structure is found by cooling isobarically down to room temperature. The proposed phase diagram suggests the occurrence of peculiar disorder-order-disorder transitions as pressure is reduced isothermally.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50288

Mesomorphic behaviour, single crystal and low angle variable temperature X-ray diffraction studies of the chloro-bridged cyclopalladated dimer obtained from 4,4'-hexyloxyazobenzene
LIQUID CRYSTALS
Autore/i: A., Crispini; M., Ghedini; S., Morrone; D., Pucci; Francescangeli, Oriano
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The newly synthesized palladium complex [(Azo-6)Pd(mu-Cl)](2), 1, [H(Azo-6)=4,4'-hexyloxyazobenzene] has been investigated by optical observations, calorimetric measurements, and single crystal and low angle variable temperature X-ray diffraction techniques. Two different mesophases appear from 210 to 220 degrees C (nematic) and above 220 until 235 degrees C (smectic E) where the compound eventually decomposes. The nematic phase is not in thermodynamic equilibrium and when subjected to an annealing process transforms into a smectic phase. The molecular structure of the dinuclear cyclopalladated complex 1 has an intramolecular Pd-Pd distance of 3.528(1)Angstrom. Moreover the molecules of 1 are arranged in pairs with an intermolecular Pd-Pd non-bonded interaction distance of 3.668(1)Angstrom. On the basis of this structural feature and of the variable temperature low-angle XRD studies, transitions involving dissociation of the molecular pairs (e.g. N(pair)reversible arrow S-E(single), on heating; N(pair)-->S-E(pair), at constant temperature) are suggested.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29742

Supramolecular ordering of bipolar lipids from Archaea in Langmuir-Blodgett films by low angle X-ray diffraction
THIN SOLID FILMS
Autore/i: S., Dante; M., DE ROSA; Francescangeli, Oriano; C., Nicolini; Rustichelli, Franco; V. I., Troitsky
Editore: Elsevier BV:PO Box 211, 1000 AE Amsterdam Netherlands:011 31 20 4853757, 011 31 20 4853642, 011 31 20 4853641, EMAIL: nlinfo-f@elsevier.nl, INTERNET: http://www.elsevier.nl, Fax: 011 31 20 4853598
Classificazione: 1 Contributo su Rivista
Abstract: The results of an investigation by X-ray diffraction on the supramolecular organization of a peculiar class of semisynthetic lipids, namely bipolar lipids from archaebacteria, when organized in layered structures in Langmuir-Blodgett films are reported. The simplicity of the experimental technique and the straightforward interpretation of the data provide a clear and unambiguous determination of the molecular conformation of bipolar lipids in LB films. The experimental data make it possible to reject unequivocally both the model of monolayers of fully extended molecules and the model of monolayers of tilted molecules, while they strongly support a structural model consisting of the stacking of bilayers made of bent U-shaped molecules. The results reported may constitute a direct clarifying contribution to the controversial matter of the molecular conformation of bipolar lipids at the air-water interface.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29590

On the limits of validity of the two-wave approximation in the dynamical theory of electromagnetic scattering by periodic dielectric media
JOURNAL DE PHYSIQUE I
Autore/i: Francescangeli, Oriano; Morini, Antonio
Classificazione: 1 Contributo su Rivista
Abstract: We investigate the accuracy and limits of validity of the two-wave approximation in the dynamical theory of electromagnetic scattering by periodic dielectric media. The errors ensuing from the approximation are estimated by applying the dynamical theory to a scattering problem for which an alternative exact electromagnetic solution is available and comparing results. The conditions for applying the approximate theory and its accuracy are discussed in terms of concepts peculiar to the classical dynamical theory of the scattering of X-rays in crystals, such as the Ewald sphere in the reciprocal space and the resonance error. After introducing the basic equations of the dynamical theory of electromagnetic scattering by three dimensional periodic dielectric media, the theory is applied to the scattering by one-dimensional periodic layered structures where a rigorous analytical solution is available. The analysis of the errors involved in the two-wave approximation indicates that, in the general case, the quality of the approximation cannot be quantified in terms of just the resonance error but it is also strongly affected by the dielectric contrast. Simple formulae are reported yielding a reliable error estimate in many practical cases. An extension of the results to the two and three dimensional case is also provided. Finally, it is suggested that a modification of the boundary conditions which are usually enforced in the dynamical theory when solving the propagation equation could improve its accuracy and extend the limits of validity of the two-wave approximation.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51834

An X-Ray Study of a Smectic C and Smectic A Liquid Crystal Polyacrylate
JOURNAL DE PHYSIQUE II
Autore/i: Francescangeli, Oriano; Rinaldi, Daniele; M., Laus; G., Galli; B., Gallot
Classificazione: 1 Contributo su Rivista
Abstract: An X-ray study was performed on powder specimens and on stretched oriented fibres of a smectic polyacrylate. The X-ray diffraction patterns showed the existence of monolayer smectic A. and bilayer smectic C mesophases that coexisted over a well defined range of temperature. In the latter mesophase the mesogenic groups were tilted with respect to the smectic layer normal by an angle beta approximate to 30 degrees. The electron density profile rho(z) along the direction normal to the smectic layers in the smectic C mesophase was determined by Fourier inversion and indicated the presence of a minor interdigitation of the terminal substituents. The phase problem related to the Fourier inversion was solved by using a pattern recognition approach based on the histogram of the electron density map. The positional smectic layer order parameters were also calculated for the first five harmonics of the positional distribution function of the smectic layers and their values suggested a well ordered layer structure.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53012

Mesophase Structure and Phase Transitions in LC Block Copolymers
ACS Polymer Preprints, Division of Polymer Chemistry
Autore/i: G., Galli; E., Chiellini; D., Wolff; D., Ferri; J., Springer; M., Laus; A. S., Angeloni; Francescangeli, Oriano
Editore: American Chemical Society
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/46508

Frequency-induced angular sweep of the electromagnetic wave diffracted by weakly curved periodic media in the dynamical regime
JOURNAL OF APPLIED PHYSICS
Autore/i: S., Melone; Francescangeli, Oriano; Caciuffo, ROBERTO GIOVANNI MARIA
Classificazione: 1 Contributo su Rivista
Abstract: The effects connected with the dynamical scattering of electromagnetic waves by weakly curved periodic layered media are discussed. A simple physical model is used to take into account the effects of the curvature in the framework of the dynamical theory of diffraction. A peculiar effect consisting of the possibility of a continuous sweep of the direction of the diffracted beam over a relatively wide angular range, under the control of the frequency of the incident wave, is seen and analyzed. The design of a device realizing such a frequency-direction conversion in the frequency range of 82-107 GHz is presented and discussed as a prototype of a new possible class of instruments.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53256

Optical Holographic Grating Formation in Dye- and Fullerene-Doped Liquid Crystalline System
Conference Proceedings: LEOS
Autore/i: Simoni, Francesco; Francescangeli, Oriano; Y., Reznikov; S., Slussarenko; I. C., Khoo; M., Wood; B. D., Guenther
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: The nonlinear optical properties of nematic liquid crystal films doped with dyes of fullerene C60 are studied. Nematic liquid crystals were doped with azo-dyes, and tested for their optical storage capabilities. An electro-optical holographic storage grating effect is observed in C60-doped nematic liquid crystal films. The effect is attributed to molecular axis reorientation caused by the combination of an applied DC field and an optically induced DC space charge. The observed nonlinear sensitivity of the films is larger than that of other materials studied.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/47221

Mesophase Behavior of Polyesther-Polymethacrylate Liquid Crystal Block Copolymers
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: G., Galli; E., Chiellini; A. S., Angeloni; M. C., Bignozzi; M., Laus; Francescangeli, Oriano
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The synthesis and properties of two series of main chain and side chain LC block copolymers constituted by a side chain LC polymethacrylate block and a main chain LC polyester block were described. The two chemically different blocks are phase segregated. The trend of the thermodynamic phase transition parameters suggests that the smectic phase of the side chain blocks provides less favourable boundary conditions than the isotropic phase of the side chain blocks and decreases the stability of both the nematic and smectic mesophases of the main chain block.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29591

Polymer dispersed liquid crystal thin films for optical processing
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Francescangeli, Oriano; I., Pepe; Simoni, Francesco
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: A shape-controlled bistable hysteresis is observed for thin polymer dispersed liquid crystal films when inserted in feedback systems where the applied voltage depends on the intensity of the light transmitted by the film. A control of the hysteresis width is possible by acting on the parameters of the feedback circuit. The possibility of obtaining bistable regions of different width can be very useful in view of the application of PDLC as optic memory elements or binary data transmission devices. An investigation on the use of these films as optical switches for fiber interconnects is also performed and the preliminary results are reported. Technical improvements are suggested in order to increase the on/off contrast ratio of the switching behavior.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29592

Liquid Crystalline Poly(vinyl ether)s and Block Copoly(vinylether)s by Living Cationic Polymerization
MACROMOLECULES
Autore/i: M., Laus; M. C., Bignozzi; M., Fagnani; A. S., Angeloni; G., Galli; E., Chiellini; Francescangeli, Oriano
Editore: American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, (800)333-9511, Fax: (202)872-4615
Classificazione: 1 Contributo su Rivista
Abstract: A series of liquid crystalline (LC) poly(vinyl ether)s 1 was prepared by living cationic polymerization of a mesogenic vinyl ether monomer, 4-butoxyphenyl 4-((6-vinylhexyl)oxy)benzoate (11), in the presence of the HI/I2 (1/1 mol/mol) initiating system. The number average molar mass of polymers 1 increased linearly with the initial monomer to initiator molar ratio (M⊙ = 3000-15 000 g mol-1, DP⊙ ≈ 5-50), according to the living character of the polymerization, and their molar mass distribution was rather narrow (MJM⊙ = 1.10-1.15). Furthermore, two sets of AB diblock copoly(vinyl ether)s 2 and 3 were prepared by sequential polymerization of vinyl ether 11 and isobutyl vinyl ether (12) and chiral (S)-2-methylbutyl vinyl ether (13) respectively, by using the same HI/I2 system. While the average degree of polymerization of the LC block was kept constant (DP⊙ ≈ 10), the length of the non-LC block was varied (DP⊙ ≈ 2-25), according to the chosen feed conditions. An X-ray investigation proved that polymers 1 gave rise to a sequence of ordered smectic (F or I), smectic C, and nematic mesophases with increasing temperature. Their transition temperatures and entropies followed slightly different molar mass dependence, but each of them reached a saturation value at M⊙ ≈ 6000 g mol-1. The same basic mesophase polymorphism was also observed for the LC block copolymers 2 and 3, thus suggesting that the chemically different blocks were microphase separated within the solid and LC phases.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29587

Hybrid Liquid-Crystalline Block Copolymers II. X-Ray Diffraction Analysis of Polyester-Polymethacrylate Block Copolymers
POLYMER JOURNAL
Autore/i: Francescangeli, Oriano; M., Laus; M. C., Bignozzi; A. S., Angeloni; G., Galli; E., Chiellini
Editore: The Society of Polymer Science, Japan (SPSJ):Tsukiji Daisan Nagaoka Building, 2-4-2 Tsukiji Chuo-ku, Tokyo 03-3502-6471 Japan:011 81 3 35026471, Fax: 011 81 3 35932709
Classificazione: 1 Contributo su Rivista
Abstract: The molecular organization in the smectic mesophases of a series of main-chain/side-chain block copolymers was studied by X-ray diffraction on oriented specimens. The main-chain and the side-chain blocks were phase-separated and gave rise to two coexisting smectic domains with different layer periodicities. The orientation of the smectic planes in the distinct domains with respect to the fiber axis was very different in the various samples and depended on the relative length of the blocks. In the presence of relatively short side-chain blocks, the orientation of the main-chain block dominated and the smectic planes of the side-chain block were forced to be parallel to those of the main-chain block and perpendicular to the fiber axis. In contrast, when the side-chain block was sufficiently long it imposed its own orientation to the main-chain block. In this case, the smectic planes of the main-chain block were oriented parallel to those of the side-chain block and to the fiber axis.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29743

On the thermal behaviour of palladium(II) macrocyclic polycatenars
LIQUID CRYSTALS
Autore/i: F., Neve; M., Ghedini; Francescangeli, Oriano
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: Polycatenar saturated macrocycles 1,10-bis[3,4,5-tris(4-dodecyloxy)benzoyl]-1,10-diaza-4,7,13,16-tetrathiacyclo-octadecane (3b) and 1,10-bis[3,4-bis(4-dodecyloxy)benzoyl]-1,10-diaza-4,7,13,16-tetrathiacyclo-octadecane (3d) reacted with [Pd(MeCN)(4)][BF4](2) led to the cationic complexes [4b][BF4](2) and [4d][BF4](2), respectively. Complexes [4b][BF4](2) and [4d][BF4](2) showed smectic mesomorphism on heating as confirmed by small angle X-ray diffraction. A concurrent, irreversible structural change of the complex cations was observed and a tentative explanation is suggested.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29589

Phase and Thermal Behavior of Liquid-Crystalline Block Copolymers
POLYMERS FOR ADVANCED TECHNOLOGIES
Autore/i: D., Wolff; D., Ferri; J., Springer; Francescangeli, Oriano; M., Laus; A. S., Angeloni; C., Bignozzi; G., Galli; E., Chiellini
Editore: John Wiley & Sons Limited:1 Oldlands Way, Bognor Regis, P022 9SA United Kingdom:011 44 1243 779777, EMAIL: cs-journals@wiley.co.uk, INTERNET: http://www.wiley.co.uk, Fax: 011 44 1243 843232
Classificazione: 1 Contributo su Rivista
Abstract: The phase behavior of liquid-crystalline (LC) block copolymers containing mesomorphic blocks with main-chain (MC) units and side-group (SG) substituents was investigated. The MC block consisted of an LC semiflexible polyester and the SG block was an LC polymethacrylate. Four different samples were prepared with the content of the SG blocks varying from 35 to 79 wt%. The thermal behavior of the copolymers was investigated using differential scanning calorimetry, and X-ray diffraction was used to characterize the phase structure. Both the MC and SG blocks formed smectic A and nematic mesophases. Thus, the occurrence of distinct and well-defined phase transitions clearly indicated that MC and SG blocks were phase-separated and showed their own phase behavior. Two different endothermic processes were identified in annealed samples that followed different kinetics. The low-temperature process is thought to involve the MC blocks in their own domains and was observed up to the smectic A to nematic transition temperature of these blocks. The high-temperature process involves the interface between MC and SG domains and is probably due to melting of crystallites grown during annealing. It is shown that the crystallization develops with kinetics affected by the degree of order of the LC state of the SG domains.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29588

EXACT SOLUTIONS FOR THE INTERGRANULAR CRITICAL STATE EQUATIONS IN HTSC MATERIALS
SCIENTIFIC BULLETIN - "POLITEHNICA" UNIVERSITY OF BUCHAREST. SERIES A, APPLIED MATHEMATICS AND PHYSICS
Autore/i: I., Pop; I., Stirbat; L., Burileanu; I., Puica; Rinaldi, Daniele; Francescangeli, Oriano; R., Caciuffo
Editore: "Politehnica" University.
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/38578

Correlations between Microstructure and a.c. Magnetic Response of Bulk Superconducting YBa2Cu3O7-x
NUOVO CIMENTO DELLA SOCIETÀ ITALIANA DI FISICA. D CONDENSED MATTER, ATOMIC, MOLECULAR AND CHEMICAL PHYSICS, BIOPHYSICS
Autore/i: Rinaldi, Daniele; I., Pop; Caciuffo, ROBERTO GIOVANNI MARIA; G., Cone; Francescangeli, Oriano; Mengucci, Paolo; A., Stepanescu; I., Stirbat
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51093

Correlations between microstructure and a.c. magnetic response of bulk superconducting YBa2Cu3O7-x
NUOVO CIMENTO DELLA SOCIETÀ ITALIANA DI FISICA. D CONDENSED MATTER, ATOMIC, MOLECULAR AND CHEMICAL PHYSICS, BIOPHYSICS
Autore/i: Rinaldi, Daniele; I., Pop; R., Caciuffo; G., Cone; Francescangeli, Oriano; Mengucci, Paolo; A., Stepanescu; I., Stirbat
Editore: Societa Italiana di Fisica:Via Saragozza 12 Subs Service, I 40123 Bologna Italy:011 39 051 331554, EMAIL: sif@sif.it, INTERNET: http://www.sif.it, Fax: 011 39 051 581340
Classificazione: 1 Contributo su Rivista
Abstract: The magnetic response of granular superconducting YBCO samples with different grain sizes is reported. The analysis is carried out by measuring the low-frequency a.c. magnetic susceptibility as a function of the temperature with an applied magnetic field of amplitude ranging between 0.4 and 800 A/m. The observed magnetic behaviour is interpreted in terms of grain size and weak-links properties. The experimental results evidence the influence of the sample microstructure on the magnetic susceptibility. The intergranular and intragranular onset temperatures are compared with the critical temperature of the samples obtained by means of electrical-resistivity measurements. The temperature dependence of the intergranular critical current density is derived from the susceptibility data.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/33263

X-ray diffraction study of a nematic-nematic transition in thermotropic liquid-crystalline polyurethanes
Liquid Crystals: Materials Science and Applications
Autore/i: Francescangeli, Oriano
Editore: J. Zmija, Z. Raszewski, J. Zielinski
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: An x-ray analysis of stretched oriented fibers of polyurethanes TDI-CmCn, derived from various mesogenic alkylene di[4-(w-hydroxyalkyloxy-4-oxybenzoyl)oxybenzoate]s (CmCn) and 2,4-toluenediisocyanate, is reported. The structure of two sequential nematic mesophases, a cybotactic nematic, and a conventional nematic mesophase is evidenced.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/47222

Hybrid Liquid-Crystalline Block Copolymers. I. Synthesis and Mesomorphic Behavior of Polyester-Polymethacrylate Block Copolymers
POLYMER JOURNAL
Autore/i: M., Laus; M. C., Bignozzi; A. S., Angeloni; Francescangeli, Oriano; G., Galli; E., Chiellini
Editore: The Society of Polymer Science, Japan (SPSJ):Tsukiji Daisan Nagaoka Building, 2-4-2 Tsukiji Chuo-ku, Tokyo 03-3502-6471 Japan:011 81 3 35026471, Fax: 011 81 3 35932709
Classificazione: 1 Contributo su Rivista
Abstract: A new type of block copolymers comprising both main-chain and side-chain liquid-crystalline (LC) blocks in the same macromolecular structure was synthesized and studied. The former was a semiflexible LC polyester block, and the latter was an LC polymethacrylate block. Thermal, dynamic-mechanical, and X-ray diffraction data indicated that the two structurally different blocks were partly phase-separated in the glassy and LC states. Significant deviations of the transition temperatures and enthalpies were observed relative to those of the corresponding homopolymers.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29239

Main-Chain/Side-Chain LC Block Copolymers
Polymers Materials Science and Engineering
Autore/i: A. S., Angeloni; M. C., Bignozzi; M., Laus; E., Chiellini; G., Galli; Francescangeli, Oriano
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/46509

An X-ray Diffraction Study of the Different Nematic Mesophases of Liquid-Crystalline Poly(urethane-ester)s
JOURNAL OF POLYMER SCIENCE. PART B, POLYMER PHYSICS
Autore/i: Francescangeli, Oriano; B., Yang; M., Laus; A. S., Angeloni; G., Galli; E., Chiellini
Editore: John Wiley & Sons Incorporated:Customer Service, 111 River Street:Hoboken, NJ 07030:(800)225-5945, (201)748-6000, EMAIL: societyinfo@wiley.com, INTERNET: http://www.wiley.com, Fax: (212)748-6551
Classificazione: 1 Contributo su Rivista
Abstract: n x-ray investigation on powder specimens and stretched oriented fibers of poly(urethane-ester)s s TDI-CmCn, derived from various mesogenic alkylene di[4-(omega-hydroxyalkyloxy-4-oxybenzoyl)oxybenzoate]s (CmCn; m = 2, 4, or 6, and n = 4, 6, 8, or 10) and 2,4-toluene-diisocyanate (TDI), is reported. Evidence is provided for the formation of two different nematic mesophases in the polymers, namely a cybotactic nematic and a conventional nematic mesophase. Whereas samples TDI-C2C6, TDI-C6C4, and TDI-C6C10 formed one cybotactic nematic mesophase, samples TDI-C4C6, TDI-C6C6, and TDI-C6C8 exhibited both cybotactic nematic and conventional nematic mesophases in a sequence with increasing temperature, which were connected by a first-order transition. The analysis of the various features of the small-angle x-ray diffraction patterns indicates that two structural arrangements, namely smectic C-like and conventional nematic structures, coexist inside the cybotactic nematic mesophase of these poly(urethane-ester)s.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29233

Macrocyclic Metallomesogens: Thermotropic Double-chained Silver Amphiphiles
JOURNAL OF MATERIALS CHEMISTRY
Autore/i: F., Neve; M., Ghedini; Francescangeli, Oriano
Editore: Royal Society of Chemistry:Thomas Graham House, Science Park, Cambridge CB4 0WF United Kingdom:011 44 1223 432360, EMAIL: sales@rsc.org, INTERNET: http://www.rsc.org, http://www.chensoc.org, Fax: 011 44 1223 423429
Classificazione: 1 Contributo su Rivista
Abstract: Mesomorphic [Ag(2)][TfO] (TfO=CF3SO3) and [Ag(2)][TsO] (TsO=p-CH3C6H4SO3) have been prepared by silver complexation of the novel N,N'-bis(hexadecanoyl)-1,10-diaza-4,7,13,16-tetrathiacyclooctadecane, 2. The phase behaviour of the silver complexes is described and a lamellar mesophase is proposed for [Ag(2)][TfO] by means of X-ray evidence.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29236

Synthesis and liquid-crystalline properties of thermotropic poly(ester-urethane)s
EUROPEAN POLYMER JOURNAL
Autore/i: A. S., Angeloni; M., Laus; E., Chiellini; G., Galli; Francescangeli, Oriano
Editore: Elsevier Science Limited:Oxford Fulfillment Center, PO Box 800, Kidlington Oxford OX5 1DX United Kingdom:011 44 1865 843000, 011 44 1865 843699, EMAIL: asianfo@elsevier.com, tcb@elsevier.co.UK, INTERNET: http://www.elsevier.com, http://www.elsevier.com/locate/shpsa/, Fax: 011 44 1865 843010
Classificazione: 1 Contributo su Rivista
Abstract: Seven new mesogenic diol monomers CmCn, consisting of two bis(p-oxybenzoyl) units interconnected by a polymethylene segment containing n methylene groups and Ranked by two linear o-hydroxyalkyl segments containing m methylene groups were reacted with 1,6-hexamethylenediisocyanate (HDI) to give a new series of liquid-crystalline poly(ester-urethane)s HDI-CmCn. All of the precursors CmCn exhibited a nematic phase, and in two of them a smectic mesophase also occurred. Poly(ester-urethane)s HDI-CmCn were semicrystalline and formed a monotropic mesophase. The mesomorphic properties of the polymers were studied as a function of their chemical structure by changing alternatively m or n. The effect of the molecular weight of the polymers on the stability of the mesophase was also investigated for various samples of poly(ester-urethane) HDI-C6C6 (M(n) = 3000-22,000). It was found that a competition existed between the tendencies of the polymer to crystallinity and liquid-crystallinity, and the molecular weight dependence of the crystallization temperature determined the onset of a monotropic mesophase.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29234

X-ray investigations on a homologous series of mesogenic azo compounds complexed with Palladium (II)
LIQUID CRYSTALS
Autore/i: A. M., Levelut; M., Veber; Francescangeli, Oriano; S., Melone; M., Ghedini; F., Neve; F. P., Nicoletta; R., Bartolino
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The X-ray diffraction experimental data concerning a homologous series of p-alkyl-p’-alkoxy-azobenzene cyclopalladated chloro-bridged dimers, both as powder and monodomain samples, are reported. These results, compared with those obtained for the parent non-metallated materials, suggest a model for the molecular arrangement wherein the alkoxy and alkyl chains are roughly coplanar with the palladium-containing rigid core and, depending on the chain length, bent towards each other.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29238

Synthesis and liquid-crystalline properties of polyacrylates containing prochiral sulfide substituents
POLYMER
Autore/i: M., Laus; A. S., Angeloni; G., Galli; E., Chiellini; Francescangeli, Oriano; B., Yang
Editore: Elsevier Science Limited:Oxford Fulfillment Center, PO Box 800, Kidlington Oxford OX5 1DX United Kingdom:011 44 1865 843000, 011 44 1865 843699, EMAIL: asianfo@elsevier.com, tcb@elsevier.co.UK, INTERNET: http://www.elsevier.com, http://www.elsevier.com/locate/shpsa/, Fax: 011 44 1865 843010
Classificazione: 1 Contributo su Rivista
Abstract: The synthesis and thermal behaviour of a new series of side-chain liquid-crystalline polyacrylates 1a-h containing prochiral alkyl sulfide substituents with a variable number n of carbon atoms are described. No liquid-crystalline behaviour was exhibited in the melt by the relevant monomers and intermediate compounds. In contrast, all polymers displayed thermotropic properties. The lower homologues 1a-f(n less than or equal to 6) displayed smectic B1 and smectic A1 mesophases, while the higher homologue 1h (n = 10) formed a bilayer, partly interdigitated smectic C mesophase. A special position was held by 1g with a sulfide substituent of intermediate length (n = 8), for which monolayer and bilayer smectic mesophases coexisted over a wide temperature range.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29235

LC block copolymers containing side-chain and main-chain blocks
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: M., Laus; M. C., Bignozzi; A. S., Angeloni; Francescangeli, Oriano; G., Galli; E., Chiellini
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The synthesis and some thermal properties of a new type of block copolymers comprising both main-chain and side-chain liquid-crystalline (LC) blocks in the same macromolecular structure are described. The former block is a semiflexible LC polyester (block A), and the latter is a LC polymethacrylate (block B). The two structurally different blocks were at least partly phase-separated within the glassy and LC states and underwent distinct phase transitions. Significant deviations of the thermodynamic parameters observed relative to those of the corresponding homopolymers suggest the occurrence of a more or less diffuse interphase.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29241

Liquid-Crystalline Side-Chain Polyacrylates Containing Chiral Sulfoxide Substituents
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Chiellini, E.; G., Galli; Angeloni, A. S.; M., Laus; S., Melone; Francescangeli, Oriano
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: A series of side-chain polyacrylates containing chiral, optically active sulfoxide substituents was prepared by the enantioselective oxidation of the corresponding prochiral polyacrylates containing prochiral sulfide substituents. A chiral sulfonyloxaziridine was used as the oxidant. The chemical modification was selective from chemical and stereochemical standpoints. The resulting polymers formed chiral nematic and/or smectic phases with a slightly decreased propensity to give stable and persistent mesophases with respect to the parent sulfide containing polymers.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29240

Methyl group tunnelling studies in calixarenes
PHYSICA. B, CONDENSED MATTER
Autore/i: Caciuffo, ROBERTO GIOVANNI MARIA; G., Amoretti; C. J., Carlile; F., Fillaux; Francescangeli, Oriano; M., Prager; F., Ugozzoli
Classificazione: 1 Contributo su Rivista
Abstract: Inelastic neutron scattering has been used to study the tunnelling of methyl groups belonging to several guest molecules (toluene, p-xylene, gamma-picoline) incarcerated in a host calixarene matrix. In all the cases investigated, the low tunnel-split librational states of the guest methyl groups. The main line occurs near 0.63 meV, very close to the CH3 quantum free rotor limit. In the toluence complex, the quantum regime persists at least up to 60 K. Effects of coupling between rotational and vibrational modes are discussed. Very subtle structural changes not revealed by diffraction measurements are suggested by the neutron spectroscopy results.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51283

Transitions metals complexed in ordered mesophases XV. Synthesis, characterization and mesomorphic properties of new potentially ferroelectric liquid crystals: Acetylacetonate p,p' -dialoxyazobenzene mononuclear palladium(II) complexes
LIQUID CRYSTALS
Autore/i: M., Ghedini; D., Pucci; E., Cesarotti; Francescangeli, Oriano; R., Bartolino
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The sysnthesis and characterization of two series of chiral mononuclear palladium(II) azocompounds, (LN (n))Pd(acac)], prepared by bridge splitting reactions or the dinuclear parents (Pd[LN (n)]μ-Cl))2 with thallium acetylacetonate are reported. All the complexes, bearing a stereogenic centre in the alkoxy lateral chain (R*O = R-(−)-2-octyl; S-(−)-β-citronellyl), are mesomorphic. Their thermotropic behaviour has been investigated by differential scanning calorimetry, optical microscopy and X-ray diffraction. Worthy of note, the clearing temperatures of all the compounds are below 70°C. The relationship between ligands, μ-Cl dimers and mononuclear acetylacetonate complexes is discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29231

Hybrid Liquid-Crystalline Block Copolymers with Polystyrene and Polyester Blocks
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: G., Galli; E., Chiellini; M., Laus; A. S., Angeloni; M. C., Bignozzi; Francescangeli, Oriano
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The synthesis and some thermal and dynamic mechanical properties of four series of liquid-crystalline block copolymers, comprising polystyrene and polyester blocks, are described. Within each series, the smectic C-nematic and nematic-isotropic transition temperatures of the polyester block were constant throughout the whole composition range, and the enthalpies of both phase transitions were directly proportional to the composition. The two blocks were incompatible in the glass and melt phases and underwent their individual phase transitions.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29180

X-ray diffraction study of the smectic C mesophase of a side chain polyacrylate containing a sulfide substituted mesogen
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Francescangeli, Oriano; S., Melone; M., Laus; A. S., Angeloni; G., Galli; E., Chiellini
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: An X-ray study was performed on powder specimen and oriented fibers of a side chain liquid-crystalline polyacrylate containing a sulfide substituent. The X-ray diffraction patterns showed the presence of a bilayer smectic C mesophase with the mesogenic groups tilted by an angle beta approximate to 40 degrees with respect to the layer normal. The electron density profile rho(z) along the direction normal to the smectic layers was calculated by Fourier inversion and the results suggest a minor interdigitation of the aliphatic chains. The positional smectic order parameter was also determined.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29181

Crystal Field Excitations and Gap Opening in Tm:YBa2Cu4O8 by Inelastic Neutron Scattering.
PHYSICA. C, SUPERCONDUCTIVITY
Autore/i: G., Amoretti; Caciuffo, ROBERTO GIOVANNI MARIA; P., Santini; Francescangeli, Oriano; E. A., Goremychkin; R., Osborn; G., Calestani; M., Sparpaglione; L., Bonoldi
Classificazione: 1 Contributo su Rivista
Abstract: We have performed a neutron spectroscopy study of Tm doped YBa2Cu4O8 using the direct geometry time-of-flight chopper spectrometer HET of the ISIS facility at the Rutherford Appleton Laboratory. Two samples were examined: a 10% doped sample with incident energy E(i)=25.2 meV and a 30% doped one with E(i) = 120 meV. The analysis of the spectra has been performed by means of a perturbation procedure, allowing us to obtain a reliable starting set of crystal field (CF) parameters for the fitting of the experimental profiles. We have investigated the temperature behaviour of the linewidth F for the two strong transitions from the ground singlet to the quasi-doublet centered at approximately 13 meV, in order to confirm the linewidth change which was observed for Tm3+ CF excitations in pure and in Zn doped YBCO (123) at a temperature T(w) higher than T(c). After correcting for the effect of the transitions between the excited states at high temperature, we have observed also in YBCO(124) an abrupt decrease of GAMMA below T(w) congruent-to 125 K, which could be attributed to the opening of an energy gap in the spectrum of the spin excitations in the CuO2 planes. By comparing the ratio T(w)/T(c) in the three compounds measured up to now, it appears that T(w)/T(c) tends to 1 at a temperature T(cm) congruent-to 93 K, corresponding, within the error bar, to the transition temperature of an ideally ''perfect'' superconductor of this family. This behaviour of T(w) has been tentatively attributed to the greater extent of 3D character in the highest-T(c) compounds. Since CF spectroscopy probes the dynamical susceptibility for omega = omega(CF), the neutron results are also discussed in comparison with NMR spectroscopy, giving complementary information on Im [chi(q, omega)] for omega-->0.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53358

The opportunity of ac technique in the study of granular high temperature superconductors
ROMANIAN REPORTS IN PHYSICS
Autore/i: I., Pop; G., Cone; I., Stirbat; I. M., Popescu; G., Majni; Caciuffo, ROBERTO GIOVANNI MARIA; Rinaldi, Daniele; Francescangeli, Oriano; A., Stepanescu
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51181

Molecular Tunnelling in p-tert-butylcalix[4]arene(2:1)p-xylene
MOLECULAR PHYSICS
Autore/i: M., Prager; Caciuffo, ROBERTO GIOVANNI MARIA; G., Amoretti; C. J., Carlile; G., Coddens; F., Fillaux; Francescangeli, Oriano; F., Ugozzoli
Classificazione: 1 Contributo su Rivista
Abstract: Inelastic neutron scattering has been used to study molecular tunnelling in the p-tert-butylcalix[4]arene(2:1)p-xylene complex. At low temperature the measured spectra show several bands between 0.63 and 2.6 meV which are interpreted as being due to transitions between tunnel-split librational states of the p-xylene methyl groups. Effects of coupling between a CH3 group and the whole p-xylene molecule have been observed. The rotational barrier provided by the host lattice is very small and the methyl groups behave as almost free quantum rotors.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53414

Transition Metals Complexed to Ordered Mesophases. Synthesis and Mesomorphic Properties of a Homologous Series of N-(4-Dodecyloxysalicylidene)-4'-Alkylanilines Complexed to Palladium(II)
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: M., Ghedini; S., Morrone; Francescangeli, Oriano; R., Bartolino
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The new [N-(4-dodecyloxysalicylidene)4'-CnH2n+1-aniline] palladium (II) derivatives, (R(n)L)(2)Pd, (1-6: n = 1-4,6,8 respectively) have been synthetized and their mesomorphic properties investigated by optical microscopy, DSC and X-ray diffraction measurements. Complexes 1-6, but 4, display a monotropic (1,5) or enantiotropic (2,3,6) smectic A mesophase. In 1-6 the geometry of the metal coordination sphere is square planar and with reference to homologous (R(n)L)(2)M compounds the mesomorphism of 1-6 appears at temperatures higher than for (R(n)L)(2)VO (distorted square pyramidal) or (R(n)L)(2)Cu (distorted square planar).
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29179

Synthesis and thermal behavior of liquid-crystalline block copolymers containing both main-chain and side-chain mesomorphic blocks
MACROMOLECULAR CHEMISTRY AND PHYSICS
Autore/i: G., Galli; E., Chiellini; M., Laus; M. C., Bignozzi; A. S., Angeloni; Francescangeli, Oriano
Editore: Wiley-VCH Verlag GmBH:PO Box 101161, D 69451 Weinheim Germany:011 49 6201 606147, EMAIL: service@wiley-vch.de, INTERNET: http://www.wiley-vch.de, Fax: 011 49 6201 606328
Classificazione: 1 Contributo su Rivista
Abstract: A novel type of block copolymers comprising both side-chain and main-chain liquid-crystalline (LC) blocks in the same macromolecular structure was synthesized and studied. The former block was either one of two LC polymethacrylates containing an azobenzene mesogen with different substituents (block A), and the latter was a semiflexible LC polyester block (block B). Thermal, dynamic-mechanical, and X-ray diffraction data indicated that the two structurally different blocks were at least partly phase-separated within the glassy and LC states. The thermodynamic phase transition parameters of block A were not affected by copolymer composition. However, significant deviations of the thermodynamic parameters of block B were observed relative to those of the corresponding homopolymers. In particular, the normalized transition enthalpies of block B were much lower, suggesting the occurrence of a more or less diffuse interphase. An increase in the nematic-isotropic temperature was found at variance with previous results on most of the LC block copolymers, in which only one block was an LC component.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/30081

Synthesis and Liquid Crystalline Properties of New Thermotropic Polyurethanes
MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY. SECTION A, MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: E., Chiellini; G., Galli; S., Trusendi; S. A., Angeloni; M., Laus; Francescangeli, Oriano
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: The synthesis and liquid crystal behavior of new thermotropic polyurethanes derived from different mesogenic diols, alkylene di[4-(omega-hydroxyalkyloxy-4-oxybenzoyl)oxybenzoate]s, and 2,4-toluenediiso-cyanate are reported. Depending upon the chemical structure of the repeat unit, the polyurethanes formed either one or two mesophases extending over a fairly broad (>60 K) and accessible range of temperature (T-i < 430 K). A cybotactic nematic mesophase was identified in each polyurethane sample.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/30083

Ionic Metallomesogens. Lamellar Mesophases in Copper(I) Azamacrocyclic Complexes
CHEMISTRY OF MATERIALS
Autore/i: F., Neve; M., Ghedini; A. M., Levelut; Francescangeli, Oriano
Editore: American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671
Classificazione: 1 Contributo su Rivista
Abstract: A series of nonmesogenic N-acylated derivatives (2) of 1,10-diaza-4,7,13,16-tetrathiacyclooctadecane (1) affords stable cationic complexes upon reaction with [Cu(MeCN)4][PF6]. The products [Cu(2)] [PF6] show thermotropic mesomorphism as a result of copper(I) complexation. Optical microscopy, calorimetry, and low-resolution powder X-ray diffraction were used to characterize the liquid-crystalline order. The presence in all complexes of a single mesophase with a lamellar structure is proposed and discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/30078

Thermal and X-ray Investigation on the Coexisting Smectic Mesophases of a Liquid Crystalline Side-Chain Polymer
MACROMOLECULES
Autore/i: G., Galli; E., Chiellini; M., Laus; A. S., Angeloni; Francescangeli, Oriano; B., Yang
Editore: American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, (800)333-9511, Fax: (202)872-4615
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/30077

Metallomesogens. Synthesis and Mesomorphic Properties of 2-Hydroxy-4-n-Alkoxy-4'-n-Alkylazobenzenes Palladium(II) Complexes
CHEMISTRY OF MATERIALS
Autore/i: M., Ghedini; S., Morrone; Francescangeli, Oriano; R., Bartolino
Editore: American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671
Classificazione: 1 Contributo su Rivista
Abstract: The synthesis and characterization of o-hydroxyazobenzene mesogens [HL(n)(m)] which form the two different homologous series HL(n)(12) (2-hydroxy-4-n-dodecyloxy-4'-n-C(n)H2n+1-azobenzenes, n = 1-4, 6, 8) and HL1(m) (2-hydroxy-4-n-C(n)H2n+1-O-4'-methylazobenzenes, m = 7, 9, 12, 14) are reported. They form N and/or S(C) mesophases at quite low temperatures. These ligands react with [Pd(PhCN)2Cl2] or Pd[(Azoxy-6)Pd(MeCN)2]BF4 giving rise to the corresponding [L(n)(m)]2Pd and {(Azoxy-6)Pd[L(n)(m)]} species [Azoxy-6 is the deprotonated form of 4,4'-bis(hexyloxy)azoxybenzene]. The [L(n)(m)]2Pd compounds are not mesogenic. On the contrary, the cyclopalladated mixed-ligand complexes, {(Azoxy-6)Pd[L(n)(m)]}, are prevalently nematogenic as optical, DSC, and X-ray analysis evidence. The {(Azoxy-6)Pd[L(n)(12)]} compounds show enantiotropic nematic (n = 1), monotropic nematic (n = 2-4, 6) and monotropic nematic and S(c) mesophases (n = 8). The {(Azoxy-6)Pd[L1(m)]} species from monotropic (m = 7, 9) and enantiotropic (m = 12, 14) nematic mesophases. A comparison between thermal behavior displayed by [L(n)(m)]2Pd and {(Azoxy-6)Pd[L(n)(m)]} complexes seems to explain the role played by the respective rigid molecular cores. The electronic and/or structural modifications induced by the azoxy group are discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/30084