88 pubblicazioni classificate nel seguente modo:

Macroscopic Biaxial Order in Multilayer Films of Bent-Core Liquid Crystals Deposited by Combined Langmuir–Blodgett/Langmuir–Schaefer Technique
NANOMATERIALS
Autore/i: Vita, F.; Adamo, F. C.; Campana, M.; Bordokas, B.; Ciuchi, F.; De Santo, M. P.; Hermida-Merino, D.; Lisovsky, A.; Pisani, M.; Pontoni, D.; Scharrer, E.; Francescangeli, O.
Classificazione: 1 Contributo su Rivista
Abstract: Bent-core liquid crystals, a class of mesogenic compounds with non-linear molecular structures, are well known for their unconventional mesophases, characterized by complex molecular (and supramolecular) ordering and often featuring biaxial and polar properties. In the nematic phase, their unique behavior is manifested in the formation of nano-sized biaxial clusters of layered molecules (cybotactic groups). While this prompted their consideration in the quest for nematic biaxiality, experimental evidence indicates that the cybotactic order is only short-ranged and that the nematic phase is macroscopically uniaxial. By combining atomic force microscopy, neutron reflectivity and wide-angle grazing-incidence X-ray scattering, here, we demonstrate that multilayer films of a bent-core nematic, deposited on silicon by a combined Langmuir–Blodgett and Langmuir–Schaefer approach, exhibit macroscopic in-plane ordering, with the long molecular axis tilted with respect to the sample surface and the short molecular axis (i.e., the apex bisector) aligned along the film compression direction. We thus propose the use of Langmuir films as an effective way to study and control the complex anchoring properties of bent-core liquid crystals.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/328032

The influence of mannose-based esters on the mesophase behaviour of lyotropic liquid crystalline nanosystems as drug delivery vectors
COLLOIDS AND SURFACES. B, BIOINTERFACES
Autore/i: Tiboni, M.; Astolfi, P.; Verboni, M.; Benedetti, S.; Giorgini, E.; Notarstefano, V.; Vita, F.; Ranieri, S.; Duranti, A.; Lucarini, S.; Casettari, L.; Pisani, M.
Classificazione: 1 Contributo su Rivista
Abstract: Lyotropic Liquid Crystalline (LLC) nanoparticles represent an emerging class of smart, biocompatible, and biodegradable systems for the delivery of drugs. Among these, structures with complex 3D architectures such as cubosomes are of particular interest. These are non- lamellar assemblies having hydrophobic and hydrophilic portions able to carry drugs of different nature. They can further be modulated including suitable additives to control the release of the active payload, and to promote an active targeting. Starting from monoolein (GMO) cubic phase, different concentrations of mannose-based esters were added, and the eventual structural modifications were monitored to ascertain the effects of the presence of glycolipids. Moreover, the structural properties of these nanosystems loaded with Dexamethasone (DEX), a very well-known anti-inflammatory steroid, were also studied. Experiments were carried out by synchrotron Small Angle X-ray Scattering (SAXS), Raman Microspectroscopy (RMS) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) measurements. The drug delivery potential (i.e. entrapment efficiency and release properties) of the obtained nanoparticles was evaluated. Finally, in vitro cytocompatibility and anti-inflammatory activity studies of the prepared formulations were carried out. Inclusion of mannose-based surfactants up to 10 mol% influenced the structural parameters of Im3m cubic phase and swollen cubic phases were obtained with the different glycolipids with lattice parameters significantly higher than GMO. A complete cytocompatibility and an increased DEX activity were observed, thus suggesting the possibility to use GMO/glycolipids nanoparticles to formulate innovative drug delivery systems.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/326431

On the Asymmetry in Photo-Induced Motion of Graphene-Oxide Paper
COATINGS
Autore/i: Castagna, R.; Riminesi, C.; Di Donato, A.; Castaldo, R.; Avolio, R.; Montalto, L.; Vita, F.; Francescangeli, O.; Lucchetta, D. E.
Classificazione: 1 Contributo su Rivista
Abstract: We report on the photo-mobility properties of a free standing large area graphene oxide (GO) paper (GOP). The thickness of the film is ≈20 (Formula presented.) m. GOP is made by drop casting an aqueous suspension of GO on a microscope glass slide placed on a hot plate kept at the temperature of 70 °C. The film is peeled-off from the glass substrate and irradiated under different coherent and incoherent light sources. The film bends up to ≈55° when the irradiation is made using a near infra-red (NIR) incoherent incandescent lamp and returns back to the initial position when the NIR lamp is switched-off. The bending mechanism is attributed to the asymmetry of the GOP film obtained during the film formation process. We characterize the film morphology and structure using a Scanning Electron Microscopy (SEM) imaging and X-ray Diffraction (XRD) measurements, respectively. Remarkable differences between the two surfaces of the GOP are evidenced, both on a macroscopic length scale (surface roughness) and on a microscopic one (GO interlayer distance). This asymmetry results in different (negative) thermal expansion coefficients for the two film surfaces and hence in the bending of the film when the film temperature is increased by light absorption.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/324531

Intercalation or external binding: How to torque chromonic Sunset Yellow
JOURNAL OF MOLECULAR LIQUIDS
Autore/i: Spina, L.; Penelope De Santo, M.; Caterina Maria, T.; Pisani, M.; Vita, F.; Barberi, R.; Ciuchi, F.
Classificazione: 1 Contributo su Rivista
Abstract: The reflection symmetry breaking observed in chromonic liquid crystals confined in different geometries, like tactoids, microspheres or capillaries, has been the focus of researchers in the last few years. Although the assembly mechanism that drives this behavior is common to most chromonic materials, the interface phenomena and the induced chirality are strongly dependent on the chromonic molecule itself. In this work, we report advances in understanding the supramolecular arrangement and induced chirality for the chromonic molecule Sunset Yellow and its interaction with salts and L-peptides. By means of optical microscopy, X-ray diffraction and atomic force microscopy, we demonstrate the rise of enhanced chirality in Sunset Yellow microspheres and propose an explanation of this phenomenon through two possible mechanisms: intercalation of the chiral dopant or binding. Our findings on the capability to control the delicate thermodynamic balance among chromonics, ions, chiral dopants, and water and its kinetics may open new perspectives for using these microspheres in optical and sensing applications.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/305902

Nanoscale Structure of Langmuir–Blodgett Film of Bent-Core Molecules
NANOMATERIALS
Autore/i: Adamo, F. C.; Ciuchi, F.; De Santo, M. P.; Astolfi, P.; Warner, I.; Scharrer, E.; Pisani, M.; Vita, F.; Francescangeli, O.
Classificazione: 1 Contributo su Rivista
Abstract: Bent-core mesogens (BCMs) are a class of thermotropic liquid crystals featuring several unconventional properties. However, the interpretation and technological exploitation of their unique behavior have been hampered by the difficulty of controlling their anchoring at surfaces. To tackle this issue, we report the nanoscale structural characterization of BCM films prepared using the Langmuir–Blodgett technique. Even though BCMs are quite different from typical amphiphilic molecules, we demonstrate that stable molecular films form over water, which can then be transferred onto silicon substrates. The combination of Brewster angle microscopy, atomic force microscopy, and X-ray reflectivity measurements shows that the molecules, once transferred onto a solid substrate, form a bilayer structure with a bottom layer of flat molecules and an upper layer of upright molecules. These results suggest that Langmuir–Blodgett films of BCMs can provide a useful means to control the alignment of this class of liquid crystals.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/305903

Cubic and Hexagonal Mesophases for Protein Encapsulation: Structural Effects of Insulin Confinement
LANGMUIR
Autore/i: Astolfi, Paola; Giorgini, Elisabetta; Romano Perinelli, Diego; Vita, Francesco; Adamo, FABRIZIO CORRADO; Logrippo, Serena; Parlapiano, Marco; Bonacucina, Giulia; Pucciarelli, Stefania; Francescangeli, Oriano; Vaccari, Lisa; Pisani, Michela
Classificazione: 1 Contributo su Rivista
Abstract: Monoolein-based cubic and hexagonal mesophases were investigated as matrices for insulin loading, at low pH, as a function of temperature and in the presence of increasing amounts of oleic acid, as a structural stabilizer for the hexagonal phase. Synchrotron small angle X-ray diffraction, rheological measurements, and attenuated total reflection-Fourier transform infrared spectroscopy were used to study the effects of insulin loading on the lipid mesophases and of the effect of protein confinement in the 2D- and 3D-lipid matrix water channels on its stability and unfolding behavior. We found that insulin encapsulation has only little effects both on the mesophase structures and on the viscoelastic properties of lipid systems, whereas protein confinement affects the response of the secondary structure of insulin to thermal changes in a different manner according to the specific mesophase: in the cubic structure, the unfolding toward an unordered structure is favored, while the prevalence of parallel β-sheets, and nuclei for fibril formation, is observed in hexagonal structures.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/291792

Synchrotron characterization of hexagonal and cubic lipidic phases loaded with azolate/phosphane gold(I) compounds: a new approach to the uploading of gold(I)-based drugs
NANOMATERIALS
Autore/i: Astolfi, Paola; Pisani, Michela; Giorgini, Elisabetta; Rossi, Barbara; Damin, Alessandro; Vita, Francesco; Francescangeli, Oriano; Luciani, Lorenzo; Galassi, Rossana
Classificazione: 1 Contributo su Rivista
Abstract: Gold(I) phosphane compounds have recently attracted a renewed interest as potential new protagonists in cancer therapy. A class of phosphane gold(I) complexes containing azolate ligands has been successfully tested against several cancer cell lines and, in particular, against basal-like breast (BLB) cancer, a form characterized by strongly severe diagnosis and short life lapse after classic chemotherapy. Even though the anticancer activity of gold(I) phosphane compounds is thoroughly ascertained, no study has been devoted to the possibility of their delivery in nanovectors. Herein, nonlamellar lyotropic liquid crystalline lipid nanosystems, a promising class of smart materials, have been used to encapsulate gold(I) azolate/phosphane complexes. In particular, ((triphenylphosphine)-gold(I)-(4,5-dichloroimidazolyl-1H-1yl)) (C-I) and ((triphenylphosphine)-gold(I)-(4,5-dicyanoimidazolyl-1H-1yl)) (C-II) have been encapsulated in three different lipid matrices: monoolein (GMO), phytantriol (PHYT) and dioleoyl-phosphatidylethanolamine (DOPE). An integrated experimental approach involving X-ray diffraction and UV resonant Raman (UVRR) spectroscopy, based on synchrotron light and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, has been employed to establish the effects of drug encapsulation on the structure and phase behavior of the host mesophases. The results indicate that gold(I) complexes C-I and C-II are successfully encapsulated in the three lipid matrices as evidenced by the drug-induced phase transitions or by the changes in the mesophase lattice parameters observed in X-ray diffraction experiments and by the spectral changes occurring in UV resonant Raman spectra upon loading the lipid matrices with C-I and C-II.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/284396

Strong graphene oxide nanocomposites from aqueous hybrid liquid crystals
NATURE COMMUNICATIONS
Autore/i: Hegde, Maruti; Yang, Lin; Vita, Francesco; Fox, Ryan J.; van de Watering, Renee; Norder, Ben; Lafont, Ugo; Francescangeli, Oriano; Madsen, Louis A.; Picken, Stephen J.; Samulski, Edward T.; Dingemans, Theo J.
Classificazione: 1 Contributo su Rivista
Abstract: Combining polymers with small amounts of stiff carbon-based nanofillers such as graphene or graphene oxide is expected to yield low-density nanocomposites with exceptional mechanical properties. However, such nanocomposites have remained elusive because of incompatibilities between fillers and polymers that are further compounded by processing difficulties. Here we report a water-based process to obtain highly reinforced nanocomposite films by simple mixing of two liquid crystalline solutions: a colloidal nematic phase comprised of graphene oxide platelets and a nematic phase formed by a rod-like high-performance aramid. Upon drying the resulting hybrid biaxial nematic phase, we obtain robust, structural nanocomposites reinforced with graphene oxide.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/275022

Liquid crystal thermosets. A new class of high-performance materials
LIQUID CRYSTALS
Autore/i: Vita, Francesco; Adamo, Fabrizio C.; Pisani, Michela; Heist, Leah M.; Li, Ming; Hegde, Maruti; Dingemans, Theo J.; Samulski, Edward T.; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/267946

Nanostructure of Unconventional Liquid Crystals Investigated by Synchrotron Radiation
NANOMATERIALS
Autore/i: Vita, Francesco; Adamo, Fabrizio Corrado; Pisani, Michela; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: The macroscopic properties of novel liquid crystal (LC) systems—LCs with unconventional molecular structure as well as conventional LCs in unconventional geometries—directly descend from their mesoscopic structural organization. While X-ray diffraction (XRD) is an obvious choice to investigate their nanoscale structure, conventional diffractometry is often hampered by experimental difficulties: the low scattering power and short-range positional order of the materials, resulting in weak and diffuse diffraction features; the need to perform measurements in challenging conditions, e.g., under magnetic and/or electric fields, on thin films, or at high temperatures; and the necessity to probe micron-sized volumes to tell the local structural properties from their macroscopic average. Synchrotron XRD allows these problems to be circumvented thanks to the superior diffraction capabilities (brilliance, q-range, energy and space resolution) and advanced sample environment available at synchrotron beamlines. Here, we highlight the potentiality of synchrotron XRD in the field of LCs by reviewing a selection of experiments on three unconventional LC systems: the potentially biaxial and polar nematic phase of bent-core mesogens; the very high-temperature nematic phase of all-aromatic LCs; and polymer-dispersed liquid crystals. In all these cases, synchrotron XRD unveils subtle nanostructural features that are reflected into macroscopic properties of great interest from both fundamental and technological points of view.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/284390

Comparative 2H NMR and x-ray diffraction investigation of a bent-core liquid crystal showing a Nematic phase
CRYSTALS
Autore/i: Ghilardi, M.; Adamo, F. C.; Vita, F.; Francescangeli, O.; Domenici, V.
Classificazione: 1 Contributo su Rivista
Abstract: Bent-core liquid crystals showing a nematic phase stable at low temperatures are very attractive for applicative purposes in view of the inherent biaxial nature of the nematic phase. In this work, a typical five-ring bent-core mesogen was investigated by means of2H NMR spectroscopy and X-ray diffraction (XRD) methods. These techniques provide complementary information on the structural properties of the nematic phase and the average mesogen conformation: Small-angle XRD reveals the presence of short-range positional order in the form of skewed cybotaxis, while a comparison of the orientational order parameters measured by wide-angle XRD and NMR provides an estimate of the molecule bend angle. In addition, 2H NMR puts in evidence the occurrence of an unexpected transition to a low-temperature tilted phase, having a crystalline or smectic-like character. The results were compared with those of previous 13C NMR investigations.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/281600

Biaxial ordering in the supercooled nematic phase of bent-core mesogens: effects of molecular symmetry and outer wing lateral groups
LIQUID CRYSTALS
Autore/i: Harkins, Robin; Tauscher, Tatum; Nguyen, Jason; Lewis, Sunny; Adamo, Fabrizio C.; Pisani, Michela; Hermida-Merino, Daniel; Samulski, Edward T.; Vita, Francesco; Francescangeli, Oriano; Scharrer, Eric
Classificazione: 1 Contributo su Rivista
Abstract: In previous research, we have found that the incorporation of three lateral substituents on bentcore oxadiazole-based liquid crystals has allowed for the presence of a nematic phase that supercooled to room temperature. X-ray diffraction (XRD) studies of these derivatives have confirmed that the nematic phase consists of cybotactic clusters. Moreover, the wide-angle XRD pattern showed a splitting indicative of local biaxial ordering within this phase. In this paper, we report the phase behaviour of two series of compounds that contain up to four lateral methyl groups. In one series, the arrangement of the lateral groups is symmetrical, and in the other case, the groups are not symmetrically distributed. All of the non-symmetric derivatives supercool to room temperature in the nematic phase, while symmetric derivatives tend to crystallise well above room temperature. XRD analysis of all of these compounds indicates the presence of cybotactic order. However, a splitting of the wide-angle XRD pattern is observed only in derivatives with lateral groups on the outer benzene rings, regardless of their supercooling behaviour, indicating the crucial influence of these substituents on the molecular packing.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/267952

Physics of matter: from the nanoscale structure to the macroscopic properties of materials
The First outstanding 50 years of "Università Politecnica delle Marche"
Autore/i: Albertini, G.; Barucca, G.; Francescangeli, O.; Lucchetta, D. E.; Lucchetti, L.; Mengucci, P.; Rinaldi, D.; Simoni, F.; Vita, F.
Editore: Springer
Classificazione: 2 Contributo in Volume
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/275117

Effects of a cationic surfactant incorporation in phytantriol bulk cubic phases and dispersions loaded with the anticancer drug 5-fluorouracil
JOURNAL OF MOLECULAR LIQUIDS
Autore/i: Astolfi, P.; Giorgini, E.; Adamo, F. C.; Vita, F.; Logrippo, Serena; Francescangeli, O.; Pisani, M.
Classificazione: 1 Contributo su Rivista
Abstract: Ordered lyotropic liquid crystalline phases, which are particularly interesting for several biological and biomedical applications, can show the advantage of having a tunable three-dimensional nanostructure. Addition of ionic surfactants to lipid/water binary systems may influence their phase behavior and their structural properties, such as bilayer thickness, water channel diameter and interfacial curvature, resulting in specific amphiphile self-assembly materials. Understanding the effects of such additives is thus of considerable interest and, in this context, we studied the incorporation of a cationic surfactant (didodecyldimethylammonium bromide) in the phytantriol cubic phase, unloaded and loaded with the anticancer drug 5-fluorouracil. In particular, an anionic form of the drug was also used which could further influence the mesophase structure of the lipid matrix and its entrapment efficiency. The formulations, prepared as bulk and dispersed phases, were characterized by synchrotron small angle X-ray scattering, attenuated total reflection Fourier transform infrared and UV–Vis spectroscopies and dynamic light scattering. Addition of increasing amounts of the cationic surfactant resulted in phase changes following the sequence Pn3m-Im3m-Lα, which was almost unaltered when the drug in its neutral form was encapsulated in the systems. On the contrary, the presence of the anionic 5-fluorouracil stabilized the Pn3m cubic phase at all the cationic surfactant concentrations used.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/267942

Polar order in bent-core nematics: An overview
JOURNAL OF MOLECULAR LIQUIDS
Autore/i: Vita, Francesco; Adamo, Fabrizio C.; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: The possible existence of a ferroelectric nematic phase has been challenging liquid crystal scientists since it was first envisaged about 30 years ago. At present, an undisputable proof of proper ferroelectricity in low-molecular weight thermotropic nematics is still missing. However, over the last decade several groups have reported the observation of a ferroelectric-like switching behavior in the nematic phase of a number of bent-core mesogens. This effect is generally ascribed to polar clusters of molecules, known as cybotactic groups, permeating the nematic phase. In the unperturbed state the cluster dipoles are randomly oriented, so that the phase is macroscopically uniaxial and apolar; however, an external field exceeding a threshold is able to align the cluster dipoles, inducing the transition to a switchable polar and biaxial state. Even though this behavior clearly differs from that expected in a proper ferroelectric liquid crystal, it still deserves considerable interest for its potential implications from both a fundamental and a technological point of view. Here we review the studies devoted to this extraordinary effect, both experiments and simulations, and discuss the open questions that still remain unanswered.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/255231

Lyotropic Liquid-Crystalline Nanosystems as Drug Delivery Agents for 5-Fluorouracil: Structure and Cytotoxicity
LANGMUIR
Autore/i: Astolfi, Paola; Giorgini, Elisabetta; Gambini, Valentina; Rossi, Barbara; Vaccari, Lisa; Vita, Francesco; Francescangeli, Oriano; Marchini, Cristina; Pisani, Michela
Classificazione: 1 Contributo su Rivista
Abstract: Lyotropic cubic liquid-crystalline systems have received increasing attention due to their unique microstructural and physicochemical properties as efficient nanocarriers for drug delivery. We report the preparation and characterization of bulk phases and cubosome dispersions of phytantriol loaded with the anticancer drug 5-fluorouracil, in neutral and anionic forms. In both cases, a Pn3m cubic phase was observed. The phytantriol phase behavior can be influenced by the addition of ionic agents, and, to this purpose, a positively charged lipid, such as N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride salt (DOTAP), was included in the studied formulations. It was found to induce a variation of the spontaneous membrane curvature of the phytantriol lipid bilayer, generating a transition from the Pn3m to the Im3m cubic phase. When 5-fluorouracil, in its anionic form (5-FUs), was encapsulated in these latter systems, a further transition to the HII hexagonal phase was observed as a consequence of the formation of a complex phytantriol/DOTAP/5-FUs. The physicochemical characterization was performed with various complementary techniques including synchrotron small-angle X-ray scattering, dynamic light scattering, and attenuated total reflection Fourier transform infrared and UV resonance Raman spectroscopies. Encapsulation of 5-fluorouracil in the corresponding nanodispersions was evaluated, and their in vitro cytotoxicity was assessed in MDA-MB-231 cell line. Phytantriol cubosomes containing 5-fluorouracil showed a higher toxicity compared with the bare drug solution, and hence they represent potential nanocarriers in the delivery of 5-fluorouracil for cancer therapy.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/251565

Short bent-core molecules: X-ray, polarization, dielectricity, texture and electro-optics investigations
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Autore/i: Torgova, S.; Sreenilayam, S. P.; Panarin, Yu. P.; Francescangeli, O.; Vita, F.; Vij, J. K.; Pozhidaev, E.; Minchenko, M.; Ferrero, C.; Strigazzi, A.
Classificazione: 1 Contributo su Rivista
Abstract: Bent-core liquid crystals based on 1,2,4-oxadiazole as a central unit have been the first mesogens to exhibit a ferroelectric response in the nematic phase. This behavior has been widely recognized as due to the presence of smectic-like polar cybotactic clusters permeating the nematic phase. Unfortunately, these compounds exhibited rather high melting points, about 120 °C, due to the presence of four benzene rings in the molecules. Here we describe the synthesis and physical characterization of a new series of BC mesogens, featuring the same bent core as the previous compounds but shorter outer substituents. By keeping only two benzene rings, we were able to lower the melting points to about 70 °C. However, while X-ray diffraction and dielectric spectroscopy measurements confirm the cybotactic nature of the nematic phase of these compounds, polarization and electro-optical measurements ascribe their polar response to flexoelectricity rather than to spontaneous polarization. Finally, texture investigation suggests the biaxiality of the nematic phase, which is indicated also by conoscopic measurements. These results are important for recognizing size and rigidity limitations in designing bent-core liquid crystal molecules suitable for applications.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/255224

Optical measurement of flow rate in a microfluidic channel
MICROFLUIDICS AND NANOFLUIDICS
Autore/i: Lucchetta, Daniele Eugenio; Vita, Francesco; Francescangeli, D.; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: A way to measure flow rate inside a microchannel using a contactless optical technique is reported. The optofluidic device consists of a Bragg grating written on a soft wall, namely a Mylar stripe glued on the top of a microfluidic channel. Diffraction of a white-light probe beam is used to detect the small displacements of the grating caused by the liquid flowing inside the microchannel. A simple model of the hydraulic circuit gives theoretical expressions for the response time of the diffracted signal allowing to fit the experimental data and determine the applied flow rates.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/230228

Micrometer-scale ordering of silicon-containing block copolymer thin films via high-temperature thermal treatments
ACS APPLIED MATERIALS & INTERFACES
Autore/i: Giammaria, Tommaso Jacopo; Ferrarese Lupi, Federico; Seguini, Gabriele; Perego, Michele; Vita, Francesco; Francescangeli, Oriano; Wenning, Brandon; Ober, Christopher K.; Sparnacci, Katia; Antonioli, Diego; Gianotti, Valentina; Laus, Michele
Classificazione: 1 Contributo su Rivista
Abstract: Block copolymer (BCP) self-assembly is expected to complement conventional optical lithography for the fabrication of next-generation microelectronic devices. In this regard, silicon-containing BCPs with a high Flory-Huggins interaction parameter (χ) are extremely appealing because they form high-resolution nanostructures with characteristic dimensions below 10 nm. However, due to their slow self-assembly kinetics and low thermal stability, these silicon-containing high-χ BCPs are usually processed by solvent vapor annealing or in solvent-rich ambient at a low annealing temperature, significantly increasing the complexity of the facilities and of the procedures. In this work, the self-assembly of cylinder-forming polystyrene-block-poly(dimethylsiloxane-random-vinylmethylsiloxane) (PS-b-P(DMS-r-VMS)) BCP on flat substrates is promoted by means of a simple thermal treatment at high temperatures. Homogeneous PS-b-P(DMS-r-VMS) thin films covering the entire sample surface are obtained without any evidence of dewetting phenomena. The BCP arranges in a single layer of cylindrical P(DMS-r-VMS) nanostructures parallel-oriented with respect to the substrate. By properly adjusting the surface functionalization, the heating rate, the annealing temperature, and the processing time, one can obtain correlation length values larger than 1 μm in a time scale fully compatible with the stringent requirements of the microelectronic industry.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/235990

Search for microscopic and macroscopic biaxiality in the cybotactic nematic phase of new oxadiazole bent-core mesogens
PHYSICAL REVIEW. E
Autore/i: Kim, Young Ki; Cukrov, Greta; Vita, Francesco; Scharrer, Eric; Samulski, Edward T.; Francescangeli, Oriano; Lavrentovich, Oleg D.
Classificazione: 1 Contributo su Rivista
Abstract: The possibility of biaxial orientational order in nematic liquid crystals is a subject of intense current interest. We explore the tendencies toward local and global biaxial ordering in the recently synthesized trimethylated oxadiazole-based bent-core mesogens with a pronounced asymmetric (bow-type) shape of molecules. The combination of x-ray diffraction and optical studies suggests that the biaxial order is expressed differently at the short- and long-range scales. Locally, at the scale of a few molecules, x-ray-diffraction data demonstrate biaxial packing. However, above the mesoscopic scale, the global orientational order in all three compounds is uniaxial, as evidenced by uniform homeotropic alignment of the nematic phase which is optically tested over the entire temperature range and by the observations of topological defects induced by individual and aggregated colloidal spheres in the nematic bulk.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/235991

Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal
SOFT MATTER
Autore/i: Vita, Francesco; Hegde, Maruti; Portale, Giuseppe; Bras, Wim; Ferrero, Claudio; Samulski, Edward T.; Francescangeli, Oriano; Dingemans, Theo
Classificazione: 1 Contributo su Rivista
Abstract: We report the structural characterization of the nematic phase of 2,6-biphenyl naphthalene (PPNPP). This lath-like all-aromatic mesogen provides a valuable benchmark for classical theories of nematic order. PPNPP exhibits a very high temperature nematic phase (417-489 °C) above an enantiotropic smectic A phase. X-ray diffraction reveals a surprisingly strong tendency towards molecular layering in the nematic phase, indicative of "normal cybotaxis" (i.e. SmA-like stratification within clusters of mesogens). Although stronger at low temperatures, the layering is evident well above the smectic A-nematic transition. The nematic order parameter is evaluated as a function of temperature from the broadening of the wide-angle diffuse diffraction feature. Measured values of the orientational order parameter are slightly larger than those predicted by the Maier-Saupe theory over the entire nematic range except for a narrow region just below the clearing point where they significantly drop below the theoretical prediction.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/235989

Search for nematic biaxiality in bent-core mesogens: an X-ray diffraction perspective
LIQUID CRYSTALS
Autore/i: Vita, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: Since its theoretical prediction in 1970, the search for the biaxial nematic phase in thermotropic systems has challenged generations of liquid crystal scientists. Over the last 10 years, bent-core mesogens have drawn much interest as promising candidates for nematic biaxiality. However, despite a number of disputed claims, conclusive evidence of proper (spontaneous and macroscopic) biaxial order in these materials is still missing. By contrast, it is now widely recognised that biaxiality exists on a local scale, in the form of nano-sized clusters of molecules (cybotactic groups) possessing smectic-like positional order and biaxial orientational order. This article provides a review of X-ray diffraction studies on biaxiality and cybotaxis in bent-core nematics, discussing the most relevant issues related to this research field.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/240944

The effects of lateral halogen substituents on the low-temperature cybotactic nematic phase in oxadiazole based bent-core liquid crystals
LIQUID CRYSTALS
Autore/i: Nguyen, Jason; Wonderly, William; Tauscher, Tatum; Harkins, Robin; Vita, Francesco; Portale, Giuseppe; Francescangeli, Oriano; Samulski, Edward T.; Scharrer, Eric
Classificazione: 1 Contributo su Rivista
Abstract: We have previously demonstrated that the incorporation of lateral methyl groups on oxadiazole-based liquid crystals leads to relatively low-temperature cybotactic nematic phases which, in some cases, supercool to room temperature. We report here the synthesis and phase behaviour of related compounds that possess lateral halogen groups and in some cases, lateral methyl groups as well. Derivatives with three lateral substituents (one halogen and two methyl groups) in a specific pattern supercool in the nematic phase to room temperature. As was the case with the previously reported trimethylated derivatives, the low-temperature nematic phase is glassy in nature. Two of the new trisubstituted derivatives (with bromo and chloro groups) remain in the nematic phase upon subsequent heating until transitioning to the isotropic phase indicating that the low-temperature nematic phase may be more stable than that shown by the trimethylated analogue. Preliminary X-ray diffraction analysis confirms the presence of a tilted cybotactic nematic phase. In addition, the splitting observed in the wide-angle scattering feature is indicative of enhanced local biaxial packing.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/229027

Molecular engineering room-temperature bent-core nematics
LIQUID CRYSTALS
Autore/i: Glebowska, A.; Vita, Francesco; Francescangeli, Oriano; Dingemans, T.; Samulski, E. T.
Classificazione: 1 Contributo su Rivista
Abstract: We report the transition temperatures for several series of structural variations on bent-core mesogens (BCMs) derived from the asymmetric oxazole biphenol mesogenic core. Trimethyl-substituted mesogens exhibit nematic phases that can be supercooled to room temperature. Preliminary X-ray diffraction (XRD) results confirm a cybotactic supramolecular organisation in these nematics; moreover, the splitting of the diffuse wide-angle XRD feature observed in trimethylated mesogens points to an enhanced biaxial orientational correlation in the transverse molecular packing compared to other BCMs. Finally, one of the trimethyl-substituted mesogens shows the formation of a room temperature metastable fibre-like crystalline order when supercooled in a magnetic field.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228984

Optical nonlinearity in the nematic phase of bent-core mesogens
OPTICS LETTERS
Autore/i: Lucchetti, Liana; Vita, Francesco; Scharrer, E.; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: Nonlinear optical response of the cybotactic nematic phase of a bent-core mesogen has been investigated for the first time through self-phase modulation induced by a Gaussian beam. The material exhibits a high nonlinear response achieving a nonlinear index n2 ≈ 5 × 10−5 cm2∕W and an unconventional behavior characterized by two different regimes. While the high-intensity regime can be easily explained in terms of a thermal indexing effect, the low-intensity regime is metastable and characterized by an unusual dependence on the irradiation energy. It is suggested that a change of the director configuration, possibly due to a light-induced modification of surface anchoring, is responsible for the observed behavior.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228982

Insights into biaxial ordering of bent-core nematics: X-ray diffraction evidence
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Vita, Francesco; Tauscher, T.; Speetjens, F.; Ferrero, C.; Samulski, E. T.; Scharrer, E.; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: Recently we have reported the first X-ray diffraction evidence of biaxial order in the fluid cybotactic nematic phase of a pair of trimethylated bent-core mesogens. This evidence is based on the splitting of the wide-angle diffuse scattering in the plane normal to the nematic director. The additional experimental data presented here provide further insights into this unprecedented behavior observed over the entire nematic phase. Although we could not determine the spatial extent of biaxial order-intracluster or intercluster-our observations reveal an enhanced biaxial orientational correlation in the transverse molecular packing, possibly reflecting stronger anisotropic interactions between nearest-neighbor mesogens.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228983

The cybotactic nematic phase of bent-core mesogens: state of the art and future developments
SOFT MATTER
Autore/i: Francescangeli, Oriano; Vita, Francesco; Samulski, E. T.
Classificazione: 1 Contributo su Rivista
Abstract: The molecular clustering observed in the fluid nematic phase of nonlinear liquid crystal molecules underlies exaggerated field effects that portend unique technological advances in next-generation liquid crystal displays. However, the detailed nature of the molecular organization within the clusters and the temporal and spatial persistence of the organization remain unclear. Herein we review the evolution of structural studies of this unique nematic phase. The mounting experimental evidence points to a converging picture of the microscopic nature of this relatively new class of liquid crystals.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/222716

Evidence of cybotactic order in the nematic phase of a main-chain liquid crystal polymer with bent-core repeat unit
ACS MACRO LETTERS
Autore/i: Vita, Francesco; Sparnacci, K.; Panzarasa, G.; Placentino, I. F.; Marino, S.; Scaramuzza, N.; Portale, G.; Di Cola, E.; Ferrero, C.; Torgova, S. I.; Galli, G.; Laus, M.; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: We report the synthesis and structural characterization of a main-chain liquid crystal polymer constituted by a 1,2,4-oxadiazole-based bent-core repeat unit. For the first time, a liquid crystal polymer made of bent mesogenic units is demonstrated to exhibit cybotactic order in the nematic phase. Coupled with the chain-bond constraints, cybotaxis results in maximized molecular correlations that make this material of great potential in the search for the elusive biaxial and ferroelectric nematic phases. Indeed, repolarization current measurements in the nematic phase hint at a ferroelectric-like switching response (upon application of an electric field of only 1.0 V μm -1) that, albeit to be definitely confirmed by complementary techniques, is strongly supported by the comparative repolarization current measurements in the nematic and isotropic phases. Finally, the weak tendency of this polymer to crystallize makes it possible to supercool the cybotactic nematic phase down to room temperature, thus, paving the way for a glassy phase in which the biaxial (and possibly polar) order is frozen at room temperature.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/158523

Evidence of Biaxial Order in the Cybotactic Nematic Phase of Bent-Core Mesogens
CHEMISTRY OF MATERIALS
Autore/i: Vita, Francesco; T., Tauscher; F., Speetjens; E. T., Samulski; E., Scharrer; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/222714

Thermally induced self-assembly of cylindrical nanodomains in low molecular weight PS-b-PMMA thin films
NANOTECHNOLOGY
Autore/i: Seguini, G.; Giammaria, T. J.; Lupi, F. F.; Sparnacci, K.; Antonioli, D.; Gianotti, V.; Vita, Francesco; Placentino, I. F.; Hilhorst, J.; Ferrero, C.; Francescangeli, Oriano; Laus, M.; Perego, M.
Classificazione: 1 Contributo su Rivista
Abstract: The phase behaviour in thin films of an asymmetric polystyrene-b- polymethylmethacrylate (PS-b-PMMA) block copolymer with a molecular weight of 39 kg mol-1 was assessed at a wide range of temperatures and times. Cylindrical PMMA structures featuring a diameter close to 10 nm and perpendicularly oriented with respect to the substrate were obtained at 180 ° C in relatively short annealing times (t ≤ 30 min) by means of a simple thermal treatment performed in a standard rapid thermal processing machine.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/158525

Fine Tuning of Lithographic Masks through Thin Films of PS-b-PMMA with Different Molar Mass by Rapid Thermal Processing
ACS APPLIED MATERIALS & INTERFACES
Autore/i: F., Ferrarese Lupi; T. J., Giammaria; G., Seguini; Vita, Francesco; Francescangeli, Oriano; K., Sparnacci; D., Antonioli; V., Gianotti; M., Laus; M., Perego
Classificazione: 1 Contributo su Rivista
Abstract: The self-assembly of asymmetric polystyrene-bpoly(methyl methacrylate) (PS-b-PMMA) block copolymer based nanoporous thin films over a broad range of molar mass (Mn) between 39 kg·mol−1 and 205 kg·mol−1 is obtained by means of a simple thermal treatment. In the case of standard thermal treatments, the self-assembly process of block copolymers is hindered at small Mn by thermodynamic limitations and by a large kinetic barrier at high Mn. We demonstrate that a fine tuning of the annealing parameters, performed by a Rapid Thermal Processing (RTP) machine, permits us to overcome those limitations. Cylindrical features are obtained by varying Mn and properly changing the corresponding annealing temperature, while keeping constant the annealing time (900 s), the film thickness (∼30 nm), and the PS fraction (∼0.7). The morphology, the characteristic dimensions (i.e., the pore diameter d and the pore-to-pore distance L0), and the order parameter (i.e., the lattice correlation length ξ) of the samples are analyzed by scanning electron microscopy and grazing-incidence small-angle X-ray scattering, obtaining values of d ranging between 12 and 30 nm and L0 ranging between 24 and 73 nm. The dependence of L0 as a 0.67 power law of the number of segments places these systems inside the strong segregation limit regime. The experimental results evidence the capability to tailor the self-assembly processes of block copolymers over a wide range of molecular weights by a simple thermal process, fully compatible with the stringent constraints of lithographic applications and industrial manufacturing.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/222713

Extraordinary field sensitivity of bent-core cybotactic nematics
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Vita, Francesco; Placentino, I. F.; Samulski, E. T.; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: Several experimental and theoretical studies conclude that the unconventional properties of bent-core nematics derive from cybotactic clusters, that is, very short-range correlation fluctuations of positional and orientational order. We show how X-ray diffraction from oxadiazole-based compounds strongly supports this model. Moreover, we recently reported an extraordinary magnetic-field-induced shift of both nematic-isotropic and smectic-C-nematic phase transition temperatures (ΔT = 4 K for B = 1 T). We review this effect, which is orders of magnitude larger than previously reported data, in the framework of the cybotactic model of bent-core nematics.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/158519

The biaxial nematic phase of oxadiazole biphenol mesogens
LIQUID CRYSTALS
Autore/i: Dingemans, T. J.; Madsen, L. A.; Francescangeli, Oriano; Vita, Francesco; Photinos, D. J.; Poon, C. D.; Samulski, E. T.
Classificazione: 1 Contributo su Rivista
Abstract: Herein we review the attributes of the cluster biaxial nematic exhibited by bent-core mesogens derived from the oxadiazole biphenol mesogenic core. We present an array of static 2H NMR spectra as well as 2D powder spectra generated by rotating the nematic phase of directly labelled mesogens. Analysis of these motionally averaged NMR observations requires the nematic phase to have monoclinic symmetry. X-ray diffraction data, in particular the effects of electric and magnetic field effects, are also consonant with the cluster picture of this biaxial nematic phase.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/158520

Electric field effect on the phase diagram of a bent-core liquid crystal
SOFT MATTER
Autore/i: Vita, Francesco; Placentino, I. F.; Ferrero, C.; Singh, G.; Samulski, E. T.; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: We have investigated the effects of a low frequency electric field on the thermotropic behavior of a nematogenic bent-core liquid crystal by means of X-ray diffraction. We have determined for the first time the 2D phase diagram of the bent-core mesogen over an extended temperature-field (T, E) space. The results show that the electric field strongly affects both the mesophase sequence and the transition temperatures of the sample. An extraordinary field-induced shift of the nematic-isotropic phase transition is found, which has neither any experimental counterpart in conventional calamitic LCs, nor can be explained by the presently available theories. The phase diagram points out the existence of exotic phase transitions driven by either electric field or temperature along specific paths in the (T, E) space. In particular, the isothermal field-induced transition from the NCybC to the N CybA phase represents a breakthrough in the interpretation of previous XRD experimental results. These experimental findings provide further strong support of the now widely accepted cybotactic cluster picture of the nematic phase of bent-core mesogens.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/158522

Laser light polarization plastic visualizer: light scattering distribution and anisotropy
RSC ADVANCES
Autore/i: A., Shalit; Lucchetta, Daniele Eugenio; L., Criante; Vita, Francesco; J. R., Tasseva; Simoni, Francesco; L., Franco; R., Bizzarri; P., Faraci; R., Conte; L., Viti; R., Kaner; R., Castagna
Classificazione: 1 Contributo su Rivista
Abstract: A laser light polarization visualizer (LPV) is obtainable by the photopolymerization of a multi-acrylate monomer, initiated by diketones under a single beam nano-pulsed (lambda = 532 nm) laser light. The derived light scattering distribution and polymer anisotropy are dependent on the polarization state of the incident-polymerizing beam. By adding a 1-haloalkane to the mixture, the solid angle of the scattered light increases. This phenomenon is dependent on the halogen of the haloalkane.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/160913

Laser emission based on first order reflection by novel compositepolymeric gratings
PHOTONICS AND NANOSTRUCTURES
Autore/i: Lucchetta, Daniele Eugenio; Vita, Francesco; Castagna, R.; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We have recently developed a novel composite photosensitive material allowing the holographic recording of diffraction gratings with high diffraction efficiency, transparency and spatial resolution. In the present work such material was used to produce a low cost and easy to make optically pumped, organic distributed feedback laser, working on the first diffraction order of a high quality grating doped with a photoluminescent dye. The experimental geometry incorporates two optical fibers which can be used to characterize the laser device in any development stage, collect emitted laser radiation, and offer an alternative way to pump the grating structure. The material properties and the used geometry allow the achievement of good performances in terms of energy threshold and linewidth. A comparison with holographic gratings made with holographic-polymer dispersed liquid crystals is reported to highlight the key role of the developed material.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/66078

Low nematic onset temperatures and room temperature cybotactic behavior in 1,3,4-oxadiazole-based bent-core mesogens possessing lateral methyl groups
JOURNAL OF MATERIALS CHEMISTRY
Autore/i: Frank, Speetjens; Jane, Lindborg; Tatum, Tauscher; Nikki, Lafemina; Jason, Nguyen; Edward T., Samulski; Vita, Francesco; Francescangeli, Oriano; Eric, Scharrer
Classificazione: 1 Contributo su Rivista
Abstract: As part of our efforts to access the biaxial nematic phase at low temperatures, we prepared a series of 1,3,4-oxadiazole-based bent-core mesogens that possess either one or three lateral methyl groups. The phase behavior of these derivatives was characterized using polarizing microscopy and differential scanning calorimetry. Target compounds containing one methyl group showed large nematic ranges but relatively high clearing points. The derivatives with three methyl substituents showed lower nematic onset temperatures and two of these compounds supercooled in the nematic phase to room temperature. X-ray diffraction experiments confirmed the presence of cybotactic clusters in the nematic phase, as observed in other bent-core mesogens. However, for two of these derivatives, cybotaxis persists at room temperature, due to the formation of a glassy nematic phase at low temperatures. These results suggest that these materials could be promising candidates in the search for low temperature biaxial thermotropic nematics.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/86395

Microfluidic transport of photopolymerizable species for laser source integration in lab-on-a-chip photonic devices
PHOTONICS AND NANOSTRUCTURES
Autore/i: Lucchetta, Daniele Eugenio; Castagna, R.; Vita, Francesco; Gianni, A.; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We recently developed a novel composite photopolymerizable material which allows the holographic recording of diffraction gratings with optimal optical and mechanical properties (high diffraction efficiency, transparency and spatial resolution, low shrinkage, long time stability). This material was successfully used to produce a low cost and easy to make optically pumped, organic distributed feedback laser, working on the first diffraction order of a high quality Bragg grating doped with a photoluminescent dye. Here we show the possibility of positioning these micrometer sized light sources at any point of a generic lab-on-a-chip device by borrowing experimental techniques commonly used in the fields of microfluidics and optofluidics. In particular, a microfluidic channel has been imprinted by soft lithography in a polydimethylsiloxane substrate in order to convey the photopolymerizable mixture to a particular area of the sample, where the laser device has been holographically recorded. A characterization of the lasing properties of this device has been carried out. The proposed approach allows a better confinement of the emitted light and overcomes some physical constrains (resolution, aspect ratio) of PDMS based microfluidic laser thus opening new possibilities for the complex integration of organic laser sources in lab-on-a-chip devices.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/73665

Extraordinary Magnetic Field Effect in Bent-Core Liquid Crystals
PHYSICAL REVIEW LETTERS
Autore/i: Francescangeli, Oriano; Vita, Francesco; Fauth, F.; Samulski, E. T.
Classificazione: 1 Contributo su Rivista
Abstract: A bent-core mesogen that forms a cybotactic nematic phase exhibits a giant magnetic field-induced shift of its nematic-isotropic and smectic-C-nematic transition temperatures: Delta T(H) = 4 K for H = 10 kOe. In contrast with molecular nematics, in cybotactic nematics the field couples with the anisotropic susceptibility of clusters containing several hundred partially ordered molecules. X-ray diffraction data corroborate a quantitative estimate of inferred cluster size (similar to 300 molecules). The results represent an unequivocal demonstration of the cluster picture of the nematic phase of this class of nonlinear liquid crystals.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/63792

Recent Developments in Nematogenic Bent-Core Mesogens: an X-ray Diffraction Perspective
JOURNAL OF NONLINEAR OPTICAL PHYSICS AND MATERIALS
Autore/i: Vita, Francesco; Placentino, IMMACOLATA FAUSTA; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: Bent-core mesogens are attracting great attention because of their potentially biaxial and polar nematic phase. In this paper, we review the results of our recent X-ray diffraction studies on the nematic phase of oxadiazole-based mesogens. The evolution of the smallangle diffraction signal with temperature points to the existence of nano-sized cybotactic clusters, characterized by short-range smectic-like fluctuations. However, in contrast to classical cybotaxis of calamitic nematics, these fluctuations do not have a pretransitional nature. They explain most of the extraordinary properties of bent-core mesogens and, in particular, are responsible for the unique ferroelectric response exhibited by one of our compounds.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/87433

Cybotaxis dominates the nematic phase of bent-core mesogens: a small-angle diffuse x-ray diffraction study
SOFT MATTER
Autore/i: Francescangeli, Oriano; Vita, Francesco; Ferrero, C.; Dingemans, T.; Samulski, E. T.
Classificazione: 1 Contributo su Rivista
Abstract: New temperature dependent X-ray diffraction (XRD) data on the bent-core mesogens based on the nonlinear 2,5-bis(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP) unit enable a consistent interpretation of the supramolecular structure in this class of liquid crystals. Strong evidence for cybotaxis in the high temperature phase explains the small-angle four-spot pattern and calls into question prior XRD interpretations. We find that the data can be satisfactorily explained by skewed cybotaxis, a stratified arrangement of tilted, bent-core mesogens (BCMs). We also observe the temperature-induced evolution of skewed cybotaxis to normal cybotaxis-strata wherein the long axes of the BCMs are normal to the layer fluctuations. Our XRD interpretation is compatible with the NMR data that exhibit biaxiality in the nematic phase of ODBP mesogens.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/66221

Holographic polymeric materials for optical processing: Microlasers, data storage and all optical switching
Information Photonics (IP), 2011 ICO International Conference
Autore/i: Lucchetta, D. E.; Vita, F.; Castagna, R.; Criante, L.; Francescangeli, O.; Simoni, F.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: We report on recent research in the field of optical processing with microlasers, high density optical storage media and all-optical switching devices. By combining different materials and optical holography some devices which show attractive optical properties and interesting wide range of potential applications will be presented.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/66223

Microlasers based on holographic PDLC structures
Liquid Crystal Microlasers
Autore/i: Simoni, Francesco; Lucchetta, Daniele Eugenio; L., Criante; Francescangeli, Oriano; Vita, Francesco
Editore: Transword Research Network
Luogo di pubblicazione: TRIVANDRUM-695 023, KERALA
Classificazione: 2 Contributo in Volume
Abstract: Invited Article
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/41779

All-optical switching of diffraction gratings infiltrated with dye-doped liquid crystals
APPLIED PHYSICS LETTERS
Autore/i: Lucchetta, Daniele Eugenio; Vita, Francesco; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We report the realization and the characterization of an all-optical switching device based on a transmission grating recorded in a polymeric substrate infiltrated with a methyl red-doped liquid crystal. The properties of this highly nonlinear mixture are exploited to modulate the diffraction of the grating by a pump beam when a static electric field is applied. The behavior of the device is in agreement with the existing model for methyl red-doped liquid crystals. (C) 2010 American Institute of Physics.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/54138

OPTICAL RANGING IN ENDOSCOPY: TOWARDS QUANTITATIVE IMAGING
ADV. IN BIOMEDICAL SENSING, LNEE 55
Autore/i: Lucesoli, Agnese; Criante, Luigino; DI DONATO, Andrea; Vita, Francesco; Simoni, Francesco; Rozzi, Tullio
Editore: Springer
Luogo di pubblicazione: BERLIN
Classificazione: 2 Contributo in Volume
Abstract: Nowadays endoscopic analysis is limited to a direct and qualitative view of internal anatomy. On the other hand, the measurement of the actual size of anatomical objects could be a powerful instrument both in research and in clinical survey. For instance, an important application could be monitoring lesion size, both during diagnosis and in follow-up. The foremost obstacle to quantitative imaging is the incapability of measuring the distance between the endoscopic probe and the anatomical object under examination, since the dimension of the object in the image depends on that distance. This problem has not been solved yet in a satisfactory way. In this Chapter we describe our work to address this problem by means of an optical measurement of the distance between the endoscope distal tip and the anatomical wall. We make use of Fiber Optics Low Coherence Interferometry to realize an absolute distance sensor compatible with endoscope technology. The result is a system integrating a clinical endoscope and an optical distance sensor, equipped with a software that allows an user to acquire an endoscopic image, select a region of interest, and obtain its quantitative measure.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/42645

Distributed feedback all-organic microlaser based on holographic polymer dispersed liquid crystals
APPLIED PHYSICS LETTERS
Autore/i: Criante, L.; Lucchetta, D. E.; Vita, F.; Castagna, R.; Simoni, F.
Classificazione: 1 Contributo su Rivista
Abstract: An optically pumped vertically emitting all-organic laser, based on a holographic polymer dispersed liquid crystal reflection grating operating in a distributed feedback configuration, is presented. The used experimental geometry overcomes the main drawbacks characterizing similar systems, allowing virtually infinite operations and absence of damages associated with the high energy of the optical pumping.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51049

Nanocomposite polymeric materials for high density optical storage
JOURNAL OF OPTICS. A, PURE AND APPLIED OPTICS
Autore/i: Criante, Luigino; Castagna, Riccardo; Vita, Francesco; Lucchetta, Daniele Eugenio; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We report the results of an extended investigation performed on composite polymeric materials with the aim of obtaining compounds suitable for holographic recording. In order to investigate the material properties a characterization of holographic reflection gratings at different writing wavelength (514.5, 457 and 405 nm) has been performed. The volume grating presents high diffraction efficiency (>60%), high sensitivity (>10(3) cm J(-1)) and refractive index modulation Delta n approximate to 0.01 even for writing wavelength in the blue range. We show that following a strategy of two basic components leading to phase separation during the photopolymerization process, most of the requirements for holographic data storage are achieved. The one that needs further improvement concerns long term mechanical stability.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52902

Modelling the dynamical behaviour of holographic gratings with nematic film-polymer slice sequence structure
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Shelestiuk, S. M.; Reshetnyak, V. Y.; Abbate, G.; Marino, A.; Vita, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: In recent years there has been much interest in the physics and possible technological applications of liquid crystal-based tuneable Bragg gratings. Such optical devices can be realised using special composite materials based on a sequence of polymeric sheets alternated by layers containing only liquid crystal, sometimes known as Policryps and Poliphem. Recent experiments have clearly demonstrated a peculiar dependence of relaxation times on actual external field applied (both amplitude and duration) after switching off the operating voltage. We propose a theoretical model of director reorientation in such composites, in which both bulk behaviour in the LC stripes and interfacial polymer-LC interaction is taken into account. Within this model we explain the dynamical behaviour of holographic gratings characterized by a nematic film-polymer slice sequence structure, as well as other polymer-LC phase separated composites.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228985

Effects of resin addition on Holographic Polymer Dispersed Liquid Crystals
JOURNAL OF OPTICS. A, PURE AND APPLIED OPTICS
Autore/i: Vita, Francesco; Lucchetta, Daniele Eugenio; Castagna, Riccardo; Criante, Luigino; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: The effects of epoxy resin addition to a standard acrylate-based holographic polymer dispersed liquid-crystal mixture are investigated. Different resin concentrations are used and we show how the presence of the resin results in transmission gratings characterized by negligible scattering, polarization independent behaviour and lower switching voltages. These experimental results are explained by means of morphological scanning electron microscopy analyses.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52224

Superior perfomance Composite Materials for High-Density Optical Data Storage
ADVANCED MATERIALS
Autore/i: Castagna, R; Vita, Francesco; Lucchetta, Daniele Eugenio; Criante, L; Simoni, Francesco
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: High-resolution holographic gratings are obtained using a combination of a multifunctional acrylate (DPHP/HA), a low-molecular-weight glass-forming liquid epoxy-aromatic resin (TPMTGE), and a UV-photoinitiator (Irgacure 819). Their optical properties (sensitivity, transparency, and optical shrinkage) are promising for high-density optical data storage applications.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/27695

Superior perfomance Composite Materials for High-Density Optical Data Storage
ADVANCED MATERIALS
Autore/i: R., Castagna; Vita, Francesco; Lucchetta, Daniele Eugenio; L., Criante; Simoni, Francesco
Editore: Composites Worldwide Incorporated:991C Lomas Santa Fe Drive, PMB469:Solana Beach, CA 92075:(858)755-1372, EMAIL: info@compositesnews.com, INTERNET: http://www.compositesnews.com, Fax: (858)755-5271
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/36386

Method and apparatus for measuring the refractive index of a material with Bragg gratings
Autore/i: Simoni, Francesco; Castagna, R.; Criante, L.; Lucchetta, Daniele Eugenio; Vita, Francesco
Classificazione: 6 Brevetti
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/58231

Holographic patterning of composite polymeric materials for photonic applications
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Criante, L; Castagna, R; Vita, Francesco; Lucchetta, Daniele Eugenio; Gobbi, Luigi; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We report the results of an extended investigation on holographic patterning of novel liquid crystal-polymer materials, developed with the aim of producing one- and two-dimensional periodic structures to be used in optical devices for data storage and processing. Characterization of reflection gratings recorded at 405 rim resulted in values of diffraction efficiency (> 60%), sensitivity (Up to 10(4) cm/J) and refractive index modulation (Delta n similar to 0.01) that make these materials interesting for optical storage applications. Large-area two-dimensional periodic structures have been also patterned using a multibeam photolitigraphic technique. These planar photonic crystals have many possible uses, both in fundamental and applied physics.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51376

Novel blue sensitive polymeric materials for optical data storage
Organic 3D Photonics Materials and Devices II
Autore/i: R., Castagna; L., Criante; Vita, Francesco; Lucchetta, Daniele Eugenio; S., Frohmann; T., Feid; S., Orlic; Simoni, Francesco
Editore: SPIE / International Society for Optical Engineering:PO Box 10:Bellingham, WA 98227:(360)676-3290, EMAIL: spie@spie.org, INTERNET: http://www.spie.org, Fax: (360)647-1445
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: We report the properties of a new polymer-guest photosensitive mixture based on two monomers with different properties as basic components. The material has been characterized by recording holographic gratings using a low power blue laser (405 nm) and a spectro-photometric technique to get the optical properties of the grating during and after recording. The detected grating shows a very high sensitivity (of the order of 10^3 cm/J) and a surprising "antishrinkage" phenomenon (red-shift of the Bragg reflection grating wavelength).
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/36385

Characterization of Optical PCB Interconnects by Means of Low-Coherence Interferometry
Optics InfoBase Conference Papers
Autore/i: Fabiani, Silvia; Farina, Marco; DI DONATO, Andrea; Lucesoli, Agnese; L., Criante; Vita, Francesco; R., Castagna; G., Angeloni; G. M., DI GREGORIO; Rozzi, Tullio
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Thanks to the low-coherence interferometry it is possible to characterize the transmission of highly dense multimode polymeric waveguides for the O-PCB. In particular the attenuation and the multi-modal dispersion are directly deduced by interferometry patterns.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50865

Haloalkane-based polymeric mixture for high density optical data storage
OPTICAL MATERIALS
Autore/i: Castagna, R; Vita, Francesco; Lucchetta, Daniele Eugenio; Criante, L; Greci, L; Simoni, Francesco
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: We present an investigation oil new organic mixtures for high resolution holographic data recording. Reflection holograms were obtained via blue laser light irradiation (lambda = 457.9 nm) on photo-sensitive acrylate and 1-chloro-hexane or 1-bromo-hexane based mixtures. These haloalkanes were selected oil the basis of their ability to originate phase separation from acrylate during the photo-polymerization process and for their lower refractive index with respect to the used poly-acrylate monomer. This last property allowed the achievement of a good dielectric contrast between polymer and haloalkane-rich layers. The recorded holograms have been investigated and optically characterized focusing on holographic data storage requirements. Finally, the results were compared with those concerning holographic polymer dispersed liquid crystal, already proposed for optical data storage applications.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/27689

At a glance determination of laser ligth polarization state
APPLIED PHYSICS LETTERS
Autore/i: Castagna, R.; Lucchetta, Daniele Eugenio; Vita, Francesco; Criante, L.; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We report a simple technique for the visual determination of a laser light polarization state. The technique is based on a phenomenon occurring when laser light impinges on a particular photopolymerizable mixture sandwiched between two glass plates. After a brief irradiation, some polarization dependent patterns are observed far from the incidence spot. This effect is due to light scattered by the polymerized material and waveguided by the glass. A visual inspection of the characteristic patterns allows an immediate determination of the light polarization. This technique could be conveniently exploited for qualitative and/or quantitative polarimetry, as well as for designing polarization-driven devices.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50265

Haloalkane-based polymeric mixture for high density optical data storage
APPLIED PHYSICS LETTERS
Autore/i: R., Castagna; Vita, Francesco; Lucchetta, Daniele Eugenio; L., Criante; L., Greci; Simoni, Francesco
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/11566/36389

Rifrattometro spettrofotometrico
Autore/i: Simoni, Francesco; Castagna, R; Criante, L; Lucchetta, Daniele Eugenio; Vita, Francesco
Classificazione: 6 Brevetti
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53623

Composizione di miscele organiche sensibili al blu usabili per l'immagazzinamento olografico dell'informazione
Autore/i: Simoni, Francesco; Castagna, R; Criante, L; Lucchetta, Daniele Eugenio; Vita, Francesco
Classificazione: 6 Brevetti
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53641

High resolution optical data storage in composite polymeric blue sensitive materials
CLEO/Europe and IQEC 2007 Conference Digest
Autore/i: Criante, Luigino; Vita, Francesco; Castagna, Riccardo; Lucchetta, Daniele Eugenio; Simoni, Francesco
Editore: Optical Society of America
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/240969

Light-polarization visualizer with polymeric composite mixtures
Optics InfoBase Conference Papers
Autore/i: Castagna, Riccardo; Lucchetta, Daniele Eugenio; Criante, Luigino; Vita, Francesco; Simoni, Francesco
Editore: Optical Society of America
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/241397

Realization and characterization of organic two-dimensional periodic structures
Optics InfoBase Conference Papers
Autore/i: Vita, Francesco; Lucchetta, Daniele Eugenio; Castagna, Riccardo; Criante, Luigino; Francescangeli, Oriano; Pierantoni, Luca; Simoni, Francesco
Editore: Optical Society of American (OSA)
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/241400

Polymeric composite materials for optical data storage and processing
2007 DIGEST OF THE LEOS SUMMER TOPICAL MEETINGS
Autore/i: Simoni, Francesco; Castagna, R.; Criante, L.; Francescangeli, Oriano; Lucchetta, Daniele Eugenio; Vita, Francesco
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: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/81893

Organic and hybrid tunable Bragg gratings for photonic devices
Liquid Crystals and Applications in Optics
Autore/i: Abbate, G; Marino, A.; Tkachenko, V.; Vita, Francesco
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: We present a survey on organic composite and hybrid materials suitable for a new family of optical devices like thermo- and electro-tunable multilayer mirrors, microcavities and optical filters. The main component is a tunable and/or switchable Bragg grating. Two different classes of materials have been realized, characterized, and designed in form of prototype devices, namely a) polymer-liquid crystal composite and b) liquid crystal infiltrated porous silicon. Different geometries and patterns can be envisaged, leading to different physical properties and a large number of device potentialities, most of them yet unexplored.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/240957

Nitroxide radicals reduce shrinkage in acrylate-based holographic gratings
OPTICAL MATERIALS
Autore/i: R., Castagna; Vita, Francesco; Lucchetta, Daniele Eugenio; L., Criante; Greci, Lucedio; P., Ferraris; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: High resolution holographic polymer dispersed liquid crystal gratings are photo-induced periodic structures commonly affected by shrinkage. This phenomenon represents a problem in several application fields such as in high density optical storage. In this work we observed that, by directly monitoring the blue-shift of the reflection peak of the periodic structure, an evident shrinkage reduction occurs using the nitroxide radical Tinuvin770-N-yloxy [(bis(2,2,6,6-tetramethyl-piperidine-1-yloxy-4-yl)-sebacate] as inhibitor of polymerization. This compound is a stable hindered amine light stabilizer-derived free radical, which plays a significant role in the photopolymerization dynamics.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53422

New composite blue sensitive materials for high resolution optical data storage
Proceedings Volume 6657, Organic 3D Photonics Materials and Devices; 665704 (2007)
Autore/i: L., Criante; Vita, Francesco; R., Castagna; Lucchetta, Daniele Eugenio; Simoni, Francesco; S., Frohmann; T., Feid; S., Orlic
Editore: Proceedings of SPIE - The International Society for Optical Engineering
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/36308

New composite blue sensitive materials for high resolution optical data storage
Organic 3D Photonics Materials and Devices
Autore/i: L., Criante; Vita, Francesco; R., Castagna; Lucchetta, Daniele Eugenio; Simoni, Francesco; S., Frohmann; T., Feid; S., Orlic
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: In the last three decades several kinds of organic mixtures for holographic recording were developed in order to achieve a new class of DVD-like optical memories for high-density optical data storage. The holographic materials should satisfy the following requirements: high sensitivity to blue light, low losses, high spatial resolution and long term stability. To this aim we developed new organic photosensitive mixtures based on only three components. We recorded high spatial frequency reflection gratings up to 7400 lines/mm with blue laser light (405 nm) by using a conventional holographic setup. We obtained a macro grating diffraction efficiency up to 67%, refractive index modulation over 0.01, optical shrinkage < 2 % and overall losses similar to 5%. In order to characterize data-storage materials independently on the experimental conditions, the sensitivity has been evaluated through the S parameter which takes into account the diffraction efficiency, recording light intensity, exposure time and sample thickness. The amazing obtained values of S >10^5 cm/J evidences a very fast recording process with a very low writing intensity (less than 20 MW/cm^2) corresponding to a recording energy density of few mJ/cm^2. The performance of these materials have been also tested in the micro-holographic geometry.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72422

Detailed investigation of high-resolution reflection gratings through angular-selectivity measurements
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. B, OPTICAL PHYSICS
Autore/i: Vita, Francesco; Lucchetta, Daniele Eugenio; Castagna, R.; Francescangeli, Oriano; Criante, L.; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We performed an investigation on Bragg reflection gratings recorded in blue-sensitive holographic polymer dispersed liquid crystals. The use of a position-sensitive detector allows selective measurements of the reflected light, never before reported in these materials, to our knowledge. We can show that by using this experimental technique it is possible to detect the formation of multiple gratings, even when the transmission spectrum does not show multiple peaks. The results are discussed in the frame of existing coupled-wave theory for anisotropic materials, allowing us to obtain the optical characterization of the gratings.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50214

Large-area photonic structures in free-standing films
APPLIED PHYSICS LETTERS
Autore/i: Vita, Francesco; Lucchetta, Daniele Eugenio; Castagna, R; Criante, L; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: The authors report the fabrication of freestanding two-dimensional photonic crystals in organic materials. Large-area patterned structures, with submicrometric spatial resolution, have been recorded in spin-coated polymer-dispersed liquid crystals via holographic photolithography. After the removal of the liquid crystal, the polymeric film is peeled off from the substrate. Scanning electron microscope images show the high homogeneity of the structure in any spatial direction. These films can be conveniently used in a wide range of applications, from templates for high-refractive index photonic crystals to flexible photonic elements.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52100

Optical characterization of liquid crystals by combined ellipsometry and half-leaky-guided-mode spectroscopy in the visible-near infrared range
JOURNAL OF APPLIED PHYSICS
Autore/i: Abbate, G.; Tkachenko, V.; Marino, A.; Vita, Francesco; Giocondo, M.; Mazzulla, A.; De Stefano, L.
Classificazione: 1 Contributo su Rivista
Abstract: In this paper, we present our results for the anisotropic refractive index measurements of commonly used liquid crystal (LC) materials (E7 and 5CB) in the whole visible-near infrared range. In order to achieve a high accuracy in the obtained values, we have employed a combination of two techniques, namely, Mueller matrix spectroscopic ellipsometry in transmission and half-leaky-guided-mode (HLGM). Measurements with the HLGM technique are usually performed at a single wavelength. In order to obtain a spectroscopic measurement based on the HLGM technique in a wide wavelength range, we modified our commercial VASE((R)) ellipsometer. In particular, we designed a sample holder by means of which measurements in guiding structures are also possible. Thus, we take advantage of the wide-spectrum light, emitted from a standard Xe lamp of the ellipsometer, also in the HLGM setup. The complementary and in-one-setup utilization of both techniques has allowed us to overcome most of the problems previously encountered in applying spectroscopic ellipsometry to the determination of the optical parameters of LC materials and eventually to achieve an accuracy in the obtained results of the order of 10(-4). We discuss how individual elements of the Mueller matrix can be used to this aim. Finally, we compare the dispersion curves for the refractive indices and the birefringence of E7 and 5CB with the data already existing in the literature.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228986

Blue sensitive mixtures for holographic optical data storage
Optics InfoBase Conference Papers
Autore/i: Castagna, Riccardo; Criante, Luigino; Lucchetta, Daniele Eugenio; Vita, Francesco; Simoni, Francesco
Editore: Optical Society of America
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/241399

Optical proprties of organic-based periodic structures
LIQUID CRYSTALS XI
Autore/i: Lucchetta, Daniele Eugenio; Vita, Francesco; R., Castagna; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Invited Paper
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/47219

Optical properties of organic-based periodic structures
Liquid Crystals XI
Autore/i: Lucchetta, Daniele Eugenio; Vita, Francesco; Castagna, R.; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/72421

Optical properties of organic-based periodic structures
Holography 2005: International Conference on Holography, Optical Recording, and Processing of Information
Autore/i: Lucchetta, Daniele Eugenio; Vita, Francesco; R., Castagna; Francescangeli, Oriano; Simoni, Francesco
Editore: SPIE / International Society for Optical Engineering:PO Box 10:Bellingham, WA 98227:(360)676-3290, EMAIL: spie@spie.org, INTERNET: http://www.spie.org, Fax: (360)647-1445
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: The aim of this work is to understand the effects of the shrinkage phenomenon in H-PDLC reflection gratings trough the real time analysis of their transmission spectra during the recording process. The real time spectroscopic analysis of the samples showed a light intensity dependent free-radical polymerization indicated by a quick growth of the reflection peak whose corresponding diffraction efficiency, measured at normal incidence, is in the range 40%-45% depending on the photopolymerization conditions. An optical shrinkage corresponding to a 4.3% displacement of the reflected wavelength from the expected value has been detected. This value of the shrinkage is in agreement to that mesaured in similar system.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/36307

Characterization of blue sensitive holographic polymer dispersed liquid crystal for microholographic data storage
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Criante, L; Vita, Francesco; Castagna, R; Lucchetta, Daniele Eugenio; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We present the results of an extended investigation performed on holographic reflection gratings recorded in blue sensitive polymer dispersed liquid crystals in view of a possible application in optical data-storage. The analysis has been performed by means of real-time spectroscopy during the polymerization process. The analysis of transmission spectra during the recording process showed a fast photopolymerization, resulting in the rapid formation of a reflection peak. Gratings characterized by high spatial frequency (> 7000 lines/mm), high diffraction efficiency (up to 50%) and large refractive index modulation (Delta n similar to 0.008) have been obtained. Unfortunately, the monomer conversion into a polymer network is generally characterized by a strong packing, with a consequent reduction in volume (polymerization shrinkage). This phenomenon induces a significant blue-shift of the reflected wavelength. With the aim of better understanding and possibly reducing the shrinkage, a new high-sensitive experimental technique has been developed to measure shrinkage effects in multi-component polymeric mixtures.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53114

High resolution optical data storage in composite polymeric materials
Optics InfoBase Conference Papers
Autore/i: Criante, L.; Vita, Francesco; Castagna, R.; Lucchetta, Daniele Eugenio; Simoni, Francesco
Editore: Optical Society of America
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: High resolution reflection gratings have been recorded at 457 nm in polymer composites. They exhibited high diffraction efficiency and sensitivity, low losses, and index modulation over 0.01. Finally recording of micro-gratings has been carried out.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228975

New generation of holographic gratings based on polymer-LC composites: POLICRYPS and POLIPHEM
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Abbate, G.; Vita, Francesco; Marino, A.; Tkachenko, V.; Slussarenko, S.; Sakhno, O.; Stumpe, J.
Classificazione: 1 Contributo su Rivista
Abstract: Soft materials exhibit very attractive mechanical, optical, and electro-optical properties and easy processing techniques. Combined with holographic techniques, they can be patterned quite easily creating many unique structures. We present here few examples, of electrically-switchable passive opto-electronic components based on composite materials obtained from initial mixtures of photocurable monomers and liquid crystalline materials. Holographic exposure results in volume gratings consisting in alternate areas of photo-crosslinked polymer and phase separated LCs, respectively. We discuss the main features of this new generation of gratings and show how most of their performances can be enhanced with respect to other kinds of composite gratings, like H-PDLCs.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228950

Nematic liquid crystal optical dispersion in the visible-near infrared range
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Tkachenko, Volodymyr; Abbate, Giancarlo; Marino, Antigone; Vita, Francesco; Giocondo, Michele; Mazzulla, Alfredo; Ciuchi, Federica; De Stefano, Luca
Classificazione: 1 Contributo su Rivista
Abstract: A commercial variable angle spectroscopic ellipsometer from J. A. Woollam Company is modified in order to make possible measurements in guiding structures. The half leaky guided mode technique is realised for liquid crystal optical dispersion measurements. Features and problems related to experimental data interpretation and error sources in the refractive index measurements are carefully analyzed, achieving a final accuracy of 0.0002. We present the measured optical dispersion curves in the wavelength range from 0.5 to 1.7 μm for two widely studied liquid crystals, namely E7 and 5CB.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228951

High accuracy optical characterization of anisotropic liquids by merging standard techniques
APPLIED PHYSICS LETTERS
Autore/i: Tkachenko, V; Abbate, G.; Marino, A.; Vita, Francesco; Giocondo, M.; Mazzulla, A.; De Stefano, L.
Classificazione: 1 Contributo su Rivista
Abstract: The design and fabrication of active and passive hybrid photonic devices, with tunable optical properties, based on liquid crystals require a very accurate knowledge of their anisotropic refractive indices up to 100 ppm in the wavelength region of interest. At this aim, the authors have integrated two standard optical techniques commonly used in liquid crystals characterization, the variable angle spectroscopic ellipsometry and the half leaky guided mode spectroscopy, exploiting their best performances and overcoming their limits. The dispersion curves of nematic liquid crystal E7 have been estimated in the 450-1700 nm wavelength interval with both precision and accuracy of 10-4.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228966

LC-polymer composites for the realization of passive and active opto-electronics components
4ª Reunión Española de Optoelectrónica, OPTOEL’05
Autore/i: Abbate, G.; Vita, Francesco; Marino, A.; Tkachenko, V.; Slussarenko, S.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: Soft materials exhibit very attracting optical/mechanical/chemical/thermal properties and flexible processing techniques. Combined with holographic fabrication techniques, they can be patterned quite easily into many unique structures. In particular, photonic crystals, and photonic quasicrystals can be fabricated this way, with little technological effort. We present here few example, based on composite materials obtained from initial mixtures of polymeric and liquid crystalline materials, of passive opto-electronic components. These components are made in the form of holographic gratings and have attracting features that will be discussed. Finally, we propose a class of active components based on similar holographic design.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228981

Visible and near-infrared characterization and modeling of nanosized holographic-polymer dispersed liquid crystals gratings
PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Autore/i: Vita, Francesco; A., Marino; V., Tkachenko; G., Abbate; Lucchetta, Daniele Eugenio; L., Criante; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We have studied the electro-optical and angular behavior of holographic-polymer-dispersed liquid crystal gratings at different wavelengths, in the visible and in the near-infrared range. As usual in these kinds of materials, a strong polarization dependent behavior was observed. Our samples showed very high diffraction efficiency for p-polarized radiation at 1.55 m, which is very interesting for many possible applications in the telecom field. However, we also observed a very unusual behavior for visible p-polarized light and we try to suggest some explanation for that. By analyzing the angular dependence of the diffraction efficiency, we could measure the components of the permittivity modulation tensor and infer important information about the main parameters involved in the grating structure: the degree of phase separation and the anisotropy in the liquid crystal droplet distribution. In our opinion, this simple and nondestructive methodology can be very useful for studying these kinds of materials and getting information on their morphology, in view of optimizing their properties. Finally, we discuss the role of the refractive index optical dispersion in order to describe the behavior of these materials at different wavelengths. These remarks are especially important when properties in the infrared range are extrapolated from measurements in the visible.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51144

Dynamical behaviour of holographic polymer-liquid crystal gratings
Proceedings of LFNM 2004 - 6th International Conference on Laser and Fiber-Optical Networks Modeling
Autore/i: Marino, A; Vita, Francesco; Tkachenko, V.; Caputo, R.; Umeton, C.; Veltri, A.; Abbate, G.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Abstract: The dynamical behavior of holographic polymer-liquid crystal grating was investigated. This grating consists of an alternate sequence of homogeneous liquid crystal films and polymer slices. The switching ON dynamics was found to depend on the pulse shape, indicating some kind of memory of the previously applied field. The main observed feature is the presence of two time constants differing one order of magnitude each other. The results indicate that the slower part of the dynamics becomes more effective for longer and more intense applied field.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228973

Spectroscopic ellipsometry study of liquid crystal and polymeric thin films in visible and near infrared
THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER
Autore/i: Tkachenko, V; Marino, A.; Vita, Francesco; D'Amore, F.; De Stefano, L.; Malinconico, M.; Rippa, M.; Abbate, G.
Classificazione: 1 Contributo su Rivista
Abstract: In this work, we propose spectroscopic ellipsometry as a suitable method for measuring optical properties in soft materials, polymers and liquid crystals, specially selected for use in photonics applications. We show the results of our measurements on some multilayered samples, in the range from visible to the near-IR region, of interest for telecom applications. We point out potentialities and limits of the technique and compare the obtained results with another experimental method, the m-lines spectroscopy, and/or with existing data in the literature. The results about the optical parameters for the analysed materials (the nematic liquid crystal 5CB, one commercial and one lab made optical polymer, and an Indium Tin Oxide film) are useful and interesting by themselves. In fact, as a paradigmatic example, we briefly discuss how an incomplete knowledge of this kind of data can lead to a wrong design of a Bragg grating device. However, more than in the provided data, we put the interest of the present analysis in the warnings about spectroscopic ellipsometry utilization and eventually the necessity of getting complementary information.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228944

Dynamical behaviour of holographic gratings with a nematic film - Polymer slice sequence structure
THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER
Autore/i: Marino, A; Vita, Francesco; Tkachenko, V.; Caputo, R.; Umeton, C.; Veltri, A.; Abbate, G.
Classificazione: 1 Contributo su Rivista
Abstract: We have studied the dynamical response of a new kind of holographic grating to a pulsed electric field. The structure, named POLICRYPS, consists of a sequence of homogeneous polymer slices separated by liquid-crystal films. We have found that both the rise and fall response times depend on the pulse duration and amplitude of the applied electric field. We propose a phenomenological explanation for this behaviour, outlining the possibility of getting response times of the order of 100 μs by properly choosing the pulse shape. Results are very interesting for developments in which POLICRYPS gratings could be proposed as basic elements in photonic devices for telecom applications, and induce to a deeper analysis of the microscopic interaction between liquid crystal and polymer interfaces in these samples.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228947

Characterization of LC-polymer composites for opto-electronic application
Proceedings of OPTOEL’03
Autore/i: Abbate, G.; Marino, A.; Vita, Francesco; Tkachenko, V.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228977

Dynamical electro-optical characterization of policryps gratings
ACTA PHYSICA POLONICA A
Autore/i: Abbate, G; Marino, A.; Vita, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We have studied the dynamical response at 633 and 1550 nm of a new polymer-liquid crystal composite, realized in a form-of a thick grating. This composite is known as Policryps, an acronym that stands for "Polymer Liquid Crystals Polymer Slides", because it shows a sequence of polymeric sheets alternated by layers containing only liquid crystal. Policryps gratings can be electrically switched between diffracting and non-diffracting states with a good diffraction efficiency in the visible region. After optimization of their performances, including response time, in the near-infrared region, they can be conveniently proposed as a key component in photonic devices for telecom applications. Our results show very interesting response times ranging from 1 to 3 ms (switching on) and from 0.1 to 0.4 ms (switching off). Furthermore, switching ON times appear to be. ruled by two different physical mechanisms with characteristic times differing by one order of magnitude. A deeper insight of these mechanisms might lead to response times, all in the submillisecond range.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228943

Policryps characterization in the near infrared
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Abbate, Giancarlo; Marino, Antigone; Vita, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We have analysed the electro-optical behaviour at 1550 nm of a new polymer and liquid crystal composite, realized in form of a thick grating. This composite is known as Policryps, acronym that stands for "Polymer Liquid Crystals Polymer Slides, because it shows a sequence of polymeric sheets alternated by layers containing only liquid crystal. Thus, by its intrinsic nature a Policryps is realized in form of grating. It is known that Policryps gratings may have a good diffraction efficiency at 633 nm and they can be electrically switched between the diffracting and non-diffracting states, with time response in the millisecond range. Eventually, Policryps may form a key component in photonic devices for use in telecom applications. With this aim, we made an optical characterization in the telecom C-band of the very first samples produced by University of Calabria (Cosenza, Italy) with this material. We measured the diffraction efficiency versus temperature and applied voltage. We also made a dynamical characterization of the grating switching. By comparison among the results obtained in the red and in the Near Infra-Red (NIR) regions, respectively, we got important information for designing and realizing Policryps samples optimised for working in the C-band.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/228941