233 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

Light-Controlled Rotational Speed of an Acoustically Levitating Photomobile Polymer Film
MATERIALS
Autore/i: Lucchetta, Daniele Eugenio; Castellini, Paolo; Martarelli, Milena; Scalise, Lorenzo; Pandarese, Giuseppe; Riminesi, Cristiano; Singh, Gautam; Di Donato, Andrea; Francescangeli, Oriano; Castagna, Riccardo
Classificazione: 1 Contributo su Rivista
Abstract: In this work, we study the light-induced changes of the rotational speed of a thin photomobile film using a single-axis acoustic levitator operating at 40 kHz. In our experiments, a 50 μm thick photomobile polymer film (PMP) is placed in one of the nodes of a stationary acoustic field. Under the action of the field, the film remains suspended in air. By externally perturbing this stable equilibrium condition, the film begins to rotate with its natural frequency. The rotations are detected in real time by monitoring the light of a low power He-Ne laser impinging on and reflected by the film itself. During the rotational motion, an external laser source is used to illuminate the PMP film; as a consequence, the film bends and the rotational speed changes by about 20 Hz. This kind of contactless long-distance interaction is an ideal platform for the development and study of many electro-optics devices in microgravity and low-friction conditions. In particular, we believe that this technology could find applications in research fields such as 3D dynamic displays and aerospace applications.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/310370

Flexible, Stretchable, Tunable, and Switchable DFB Laser
PHOTONICS
Autore/i: Lucchetta, Daniele Eugenio; Di Donato, Andrea; Francescangeli, Oriano; Riminesi, Cristiano; Singh, Gautam; Castagna, Riccardo
Classificazione: 1 Contributo su Rivista
Abstract: We are reporting on easily-made, flexible, wearable, and stretchable holographic gratings for tunable distributed-feedback lasers. The laser device is formed by the integration of a reflection volume phase grating in a flexible substrate. The grating is recorded in a photopolymerizable mixture by using optical holography. The photopolymerizing material is a new compound derived from a recently developed mixture which is based largely on haloalkanes and acrylates. An appropriate choice of photoinitiators promotes the photoactivation of the monomers at the writing wavelength of 460 nm. The laser device has a low emission threshold due to the high efficiency of the photopolymerization process at 460 nm. Finally, the amplified spontaneous emission of the device can be continuously tuned by simply bending the film. This peculiarity is promising for the manufacturing of optical pumped tunable organic lasers and flexible displays.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/310369

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

Development of a Quartz-Based Photo-Mobile Polymer Film for Controlled Motion Triggered by Light or Heat
MATERIALS
Autore/i: Castagna, R.; Riminesi, C.; Pianesi, M. S.; Sabbatini, S.; Di Donato, A.; Singh, G.; Francescangeli, O.; Cantisani, E.; Castellini, P.; Lucchetta, D. E.
Classificazione: 1 Contributo su Rivista
Abstract: We have developed a photo-mobile polymer film, that combines organic and inorganic materials, to allow for controlled motion that can be triggered by light or heat. Our film is made using recycled quartz and consists of two layers: a multi-acrylate polymer layer and a layer containing oxidized 4-amino-phenol and N-Vinyl-1-Pyrrolidinone. The use of quartz in our film also gives it a high temperature resistance of at least 350 °C. When exposed to heat, the film moves in a direction that is independent of the heat source, due to its asymmetrical design. Once the heat source is removed, the film returns to its original position. ATR-FTIR measurements confirm this asymmetrical configuration. This technology may have potential applications in energy harvesting, due to the piezoelectric properties of quartz.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/316313

On the Use of Haloalkane/Acrylate-Based Holographic Gratings as Compression and Rotation Sensors
SENSORS
Autore/i: Castagna, R.; Riminesi, C.; Di Donato, A.; Francescangeli, O.; Lucchetta, D. E.
Classificazione: 1 Contributo su Rivista
Abstract: In this work, we test the effectiveness of using highly transparent holographic phase reflection and transmission volume gratings based on multifunctional acrylates as linear compression and rotation sensors. The gratings are recorded in a holographic mixture based on multi-reticulated acrylate and haloalkanes. To activate the photo-polymerization process, we used a mixture of 6-oxocamphore and rhodamine 6G. The mixture is a simplified version of the mixture used in previous works and shows some interesting features mainly in connection with the different roles played by the rhodamine 6G dye at different writing wavelengths (Formula presented.) = 532 nm and (Formula presented.) = 460 nm. Regarding reflection gratings, the maximum achieved diffraction efficiency is ≈50% and their use as linear compression sensors produces a shift in the reflection peak of 2 nm. Following the removal of compression, the grating slowly returns to the initial state. Regarding transmission gratings, the maximum achieved diffraction efficiency is ≈45% and they demonstrate very high sensitivity to even small rotations in a free-standing configuration.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/309987

Polymer-Based High Diffraction Efficiency and High Resolution Volume Holographic Transmission Gratings
CHEMOSENSORS
Autore/i: Castagna, Riccardo; Di Donato, Andrea; Francescangeli, Oriano; Lucchetta, Daniele Eugenio
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/306064

Scotch-Tape and Graphene-Oxide Photomobile Polymer Film
PHOTONICS
Autore/i: Castagna, R; Di Donato, A; Castaldo, R; Avolio, R; Francescangeli, O; Lucchetta, De
Classificazione: 1 Contributo su Rivista
Abstract: In this work, we report on the fabrication and photonic activation of a novel kind of photomobile polymer (PMP) film based mainly on a double layered asymmetric configuration. The PMP is cheap and extremely easy to make. It is made of PVC/isoprene tape with a layer of graphene-oxide (GO) attached. Under illumination at different intensities, and with coherent and incoherent light sources, the bending of the PMP film changes considerably. In particular, we noticed a more efficient bending effect when the film is directly exposed to high light intensities or to NIR radiation in the case of incoherent light sources. For the exposure times used in our experiments, the process is completely reversible when the light source is switched off. Additionally, if we paint the side of the PVC tape exposed to light black, the film is not able to return to its starting position and the bending results are permanent. This suggests that the presence of the GO-layer is responsible for the restoration of the position of the PMP film.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/306901

Top-Performance Transmission Gratings with Haloalkanes-Based Polymeric Composite Materials
MATERIALS
Autore/i: Castagna, R.; Riminesi, C.; Di Donato, A.; Francescangeli, O.; Lucchetta, D. E.
Classificazione: 1 Contributo su Rivista
Abstract: We report on highly transparent holographic phase transmission volume gratings recorded in the visible region at (Formula presented.) = 532 nm. The maximum measured diffraction efficiency is higher than 80% with a grating pitch of (Formula presented.) ≈ 300 nm and a refractive index modulation (Formula presented.) n ≈ 0.018. To obtain these results, we used a holographic mixture based on multi-reticulated acrylate and haloalkanes (1-bromo-butane and 1-bromo-hexane) and a synergic combination of camphore-quinone, which has a maximum absorbance at c.a. 470 nm, and R6G, here used as co-initiator, to efficiently initiate the photo-polymerization process. High transparent and high efficient holographic structures based on polymers can find applications in many research fields including integrated optics, sensors, high density data storage and security.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/309262

Optically Tunable Diffraction Efficiency in Reflection Grating Written in Photomobile Polymers
PHOTONICS
Autore/i: Castagna, Riccardo; Di Donato, Andrea; Francescangeli, Oriano; Lucchetta, Daniele Eugenio
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/307781

Light-Controlled Direction of Distributed Feedback Laser Emission by Photo-Mobile Polymer Films
NANOMATERIALS
Autore/i: Lucchetta, De; Di Donato, A; Francescangeli, O; Singh, G; Castagna, R
Classificazione: 1 Contributo su Rivista
Abstract: We report on the realization of Distributed Feedback (DFB) lasing by a high-resolution reflection grating integrated in a Photomobile Polymer (PMP) film. The grating is recorded in a recently developed holographic mixture basically containing halolakanes/acrylates and a fluorescent dye molecule (Rhodamine 6G). The PMP-mixture is placed around the grating spot and a subsequent curing/photo-polymerization process is promoted by UV-irradiation. Such a process brings to the simultaneous formation of the PMP-film and the covalent link of the PMP-film to the DFB-grating area (PMP-DFB system). The PMP-DFB allows lasing action when optically pumped with a nano-pulsed green laser source. Moreover, under a low-power light-irradiation the PMP-DFB bends inducing a spatial readdressing of the DFB-laser emission. This device is the first example of a light-controlled direction of a DFB laser emission. It could represent a novel disruptive optical technology in many fields of Science, making feasible the approach to free standing and light-controllable lasers.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/306063

HKUST-1-Doped High-Resolution Volume Holographic Gratings
CHEMOSENSORS
Autore/i: Castagna, R; Tombesi, A; Riminesi, C; Di Donato, A; Francescangeli, O; Lucchetta, De
Classificazione: 1 Contributo su Rivista
Abstract: We report on transmission holographic gratings doped with metal organic frameworks (MOFs). As a first attempt, we focused on MOF-199, also known as HKUST-1, which is an efficient adsorbent of VOCs. HKUST-1 is not soluble in the pre-polymerized holographic mixture. For this reason, samples containing HKUST-1 show high light scattering. In this work, the recording of HKUST-1-doped one-dimensional transmission phase gratings is demonstrated. The optical properties of the recorded structures, such as diffraction efficiency and average refractive index changes, are reported by using angular analysis measurements. A first attempt to demonstrate the possibility of using the doped gratings as sensors is also reported.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/306062

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

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

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

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

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

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

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

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

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

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

Trans-cis photoisomerization in nanostructured floating layers and x-ray diffraction study of Langmuir-Schaefer films of nonyloxypheylazocinnamic acid
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Pisani, Michela; Maiorova, L. A.; Francescangeli, Oriano; Fokin, D. M. S.; Nikitin, K. S.; Burmistrov, V. A.; Kuvshinova, S. A.; Mengucci, Paolo; Koifman, O. I.
Classificazione: 1 Contributo su Rivista
Abstract: Azo-functionalised materials are of special interest due to their photochromic nature, i.e. reversible trans–cis isomerisation upon photoirradiation. The structure and properties of Langmuir monolayers of nonyloxyphenylazocinnamic acid (NOPACA) with and without exposure to UV-irradiation were studied. The NOPACA floating layer structure was determined by using a quantitative method of compression isotherm analysis. The results showed that the structure of two dimensional face-on M-nanoaggregates, the stable structural elements of floating monolayers, changes when exposed to UV-irradiation. Langmuir-Schaefer films of NOPACA were prepared by deposition of floating layers and studied using X-ray diffraction technique.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/250593

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

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

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

Elliptical Small-Angle X-Ray Scattering Patterns from Aligned Lamellar Arrays
JOURNAL OF POLYMER SCIENCE. PART B, POLYMER PHYSICS
Autore/i: Grubb, David; Murthy, N. Sanjeeva; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: Semicrystalline polymers aligned by drawing into films or fibers produce small-angle X-ray scattering patterns with two or four spots. Some liquid crystalline materials, cybotactic nematics, produce extremely similar patterns when oriented in magnetic fields. A structure of stacked lamellae, tilted for four point patterns, explain the basic features. However, the peak intensity positions of the broadened reflections lie not on a layer line or on the arc of a circle, but very close to an ellipse. Specific structural explanations of this feature have been suggested, but models using an equilibrium distribution of molecular orientations and lamellar tilts can predict elliptical shapes for the reflections. The model parameters are chosen by fitting the entire 2D intensity distribution of the scattering pattern. Assumptions required for modeling make some fitted parameters uncertain, but it is clear that the elliptical form can emerge from a statistical distribution of the properties of the stacks of lamellae, without a directly assignable structural cause.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/236896

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

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

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

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

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

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 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

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

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

An X-ray diffraction study of complexes of DNA and lactosyl-functionalised liposomes induced by bivalent metal cations: coexistence of different symmetries
LIQUID CRYSTALS
Autore/i: Pisani, Michela; Mobbili, Giovanna; Marini, Milvia; Francescangeli, Oriano; Mori, Valerio; Bruni, Paolo
Classificazione: 1 Contributo su Rivista
Abstract: By using synchrotron X-ray diffraction we studied the structure and phase behaviour of complexes of DNA with the anionic 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-lactosyl (L-PE), mixed with zwitterionic lipids 1,2-dioleoyl-sn-glycero 3-phosphocholine (DOPC) or 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), in aqueous solutions of Mn2+ and Ca2+. Aqueous dispersions of simple L-PE/DOPC and L-PE/DOPE in the presence and absence of metal cations were also studied. All the systems complexed in a self-assembled manner, the DNA condensation being promoted by the metal cations. These complexes are organised in a variety of structures showing a number of symmetries, sometimes coexisting, for example condensed multilamellar, Lαc, inverted hexagonal, HIIc, and cubic, Pn3m. Phase distribution depends on the molar ratios between L-PE and DOPC or DOPE, respectively.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/164742

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

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

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

Uniaxial to biaxial nematic phase transition in a bent-core thermotropic liquid crystal by polarising microscopy
LIQUID CRYSTALS
Autore/i: Picken, S. J.; Dingemans, T. J.; Madsen, L. A.; Francescangeli, Oriano; Samulski, E. T.
Classificazione: 1 Contributo su Rivista
Abstract: Cover Journal Article
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/66222

Can Neutral Liposomes be Considered as Genetic Material Carriers for Human Gene Therapy?
MINI-REVIEWS IN ORGANIC CHEMISTRY
Autore/i: Bruni, Paolo; Francescangeli, Oriano; Marini, Milvia; Mobbili, Giovanna; Pisani, Michela; Smorlesi, Arianna
Classificazione: 1 Contributo su Rivista
Abstract: Among the synthetic vectors exploitable in Human Gene Therapy (HGT), complexes of DNA with cationic liposomes (lipoplexes) are considered the best candidates. Some degree of cytotoxicity and a limited stability on serum are still limiting factors for applications in vivo. On the contrary the corresponding complexes of neutral liposomes are enough stable and non toxic. This review has the aim to offer a survey of existing data, namely structural properties, on neutral liposomes from the point of view of HGT; and to compare, whenever possible, the different features of the two classes of compounds. The outlook is that in near future neutral liposomes could behave as efficient and safe vectors of genetic material.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/58329

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

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

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

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

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

Insights into the cybotactic nemaic phase of bent-core mesogens
SOFT MATTER
Autore/i: Francescangeli, Oriano; E. T., Samulski
Classificazione: 1 Contributo su Rivista
Abstract: We present X-ray diffraction evidence for clusters exhibiting a skewed cybotactic supramolecular structure in the nematic phase of the butyloxy-phenyl diester, ODBP-Ph-OC4, a bent core mesogenic diester of the nonlinear diol 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP). The temperature dependence of the off-meridional four-spot pattern shows that the tilt angle in the cybotactic clusters changes with temperature. The correlation lengths exhibit no evidence of critical behavior but there is no underlying smectic C phase in ODBP-Ph-OC4. The tilted cybotactic clusters persist throughout the 85 C wide nematic phase, and even remain evident in the supercooled nematic. This inherently biaxial supramolecular structure—clusters of stratified and tilted mesogens—embedded in an otherwise translationally disordered nematic host medium may account for the NMR biaxiality observed in nematic phases of ODBP mesogens.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/30127

Nanostructure and Biological Function of Self-Assembled Liposome-DNA-Metal Complexes for Gene Therapy
Proceedings of the International School on Advanced Material Science and Technology, Nanobiotechnologies and Nanomedicine
Autore/i: Francescangeli, Oriano; Pisani, Michela; V., Fino; Bruni, Paolo
Editore: Edizioni GEI - Fondazione Cassa di Risparmio di Jesi
Luogo di pubblicazione: JESI
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53460

12-Crown-4-based amphipatic lipid and corresponding metal cation complexes for gene therapy applications: FT-IR characterization and surface charge determination
JOURNAL OF MOLECULAR STRUCTURE
Autore/i: Bruni, P; Fino, V; Pisani, Michela; Tosi, Giorgio; Stipa, Pierluigi; Ferraris, P; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: The new lipid 1,2-O-dioleyl-3-O-{2-[(12-crown-4)-methoxy]-ethyl}-sn-glycerol, 12C4L, has been synthesized. This molecule can coordinate different cations that should make the corresponding liposome a good candidate as vector of genetic material for possible applications in gene therapy. An important feature of the molecule is the possibility to modulate the net surface charge of their complexes with metal cations, which is important to provide efficient DNA transfections. The molecule and its complexes with some metal cations (Mg2+, Ca2+, Mn2+) have been characterized by FT-IR spectroscopy and band attributions confirmed by Density Functional Theory calculations. The net surface charge has been determined by Z potential determinations.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50926

DNA Condensation into Inverted Hexagonal Phase in Aqueous Dispersion of Poly(Ethylene)-Functionalized Dioleoylphosphatidylethanolamine and Metal Cations
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Pisani, Michela; Fino, V.; Bruni, Paolo; Francescangeli, Oriano
Editore: TAYLOR & FRANCIS LTD, 4 PARK SQUARE, MILTON PARK, ABINGDON, ENGLAND, OXON, OX14 4RN
Classificazione: 1 Contributo su Rivista
Abstract: We report the x-ray diffraction study of the structure and phase behavior of mixtures of dioleoylphosphatidylethanolamine (DOPE) and poly(ethyleneglycol)- functionalized DOPE (DOPE:PEG(350)) in aqueous dispersions of DNA and bivalent metal cations. Characterization of the phase behaviour of DOPE/DOPE:PEG(350) mixtures in presence of metal cations without DNA is also performed: over a definite amount of the PEG-lipid component, a phase transition from the inverted hexagonal phase HII to the bicontinuous inverted cubic phase, with space group Pn3m is induced. Moreover, it is shown that at low concentration of PEG-lipid component, the inverted hexagonal phase [image omitted] is found on adding DNA to the aqueous dispersions of DOPE/DOPE:PEG and metal cations. This structure consists of cylindrical DNA strands coated by neutral lipid monolayers and arranged on a two-dimensional hexagonal lattice. The results here shown represent the first experimental evidence of a self-assembled formation of an inverted hexagonal complex structure in aqueous dispersions of DNA, metal cations and liposomes made of mixtures of pure and pegylated lipids. The surface functionalization with the PEG-lipid and the evidence of the formation of the complexes are important results in the perspective of the development of appropriate vectors for drug delivery and gene transfection.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50160

Ferroelectric Response and Induced Biaxiality in the Nematic Phase of a Bent-Core Mesogen
ADVANCED FUNCTIONAL MATERIALS
Autore/i: Francescangeli, Oriano; V., Stanic; S. I., Torgova; A., Strigazzi; N., Scaramuzza; C., Ferrero; I. P., Dolbnya; T. M., Weiss; R., Berardi; L., Muccioli; S., Orlandi; C., Zannoni
Classificazione: 1 Contributo su Rivista
Abstract: The still undiscovered fluid ferroelectric nematic phase is expected to exhibit a much faster and easier response to an external electric field compared to conventional ferroelectric smectic liquid crystals; therefore, the discovery of such a phase could open new avenues in electro-optic device technology. Here, experimental evidence of a ferroelectric response to a switching electric field in a low molarmass nematic liquid crystal is reported and connected with field-induced biaxiality. The fluid is made of bent-core polar molecules and is nematic over a range of 120 -C. Combining repolarization current measurements, electro-optical characterizations, X-ray diffraction and computer simulations, ferroelectric switching is demonstrated and it is concluded that the response is due to field-induced reorganization of polar cybotactic groups within the nematic phase. This work represents significant progress toward the realization of ferroelectric fluids that can be aligned at command with a simple electric field.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/30126

Structure and supramolecular organization of a new class of self-assembled Lipid-DNA-Metal Complexes for gene transfer
8° Congresso Nazionale della Società Italiana dei Cristalli Liquidi
Autore/i: Pisani, Michela; V., Fino; P., Bruni; Francescangeli, Oriano
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83378

Metal Cation Induced Cubic Phase in Poly(ethylene glycol)-Functionalized Dioleoylphosphatidylethanolamine Aqueous Dispersions
JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL
Autore/i: Pisani, Michela; V., Fino; P., Bruni; E., DI COLA; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: Metal cations (Mn2+ or Ca2+) in aqueous dispersions of mixtures of dioleoylphosphatidylethanolamine (DOPE) and poly(ethylene glycol)-functionalized DOPE (DOPE-PEG(350)) induce, above a certain amount of the PEG lipid component, a phase transition from the inverted hexagonal phase HII to the bicontinuous inverted cubic phase Q224 with space group Pn3m. The process is driven by the decrease of free elastic energy due to the Gaussian curvature of the cubic phase. The structural characterization of the phase behavior over the whole explored range of DOPE-PEG/DOPE weight ratio (3−25%) is reported, focusing on the role of the metal cation in the formation of the 3D cubic lattice. This result may represent a significant progress toward a design-based approach to drug delivery.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53086

Liposomi-DNA:Nuovi sistemi per il trasporto di materiale genetico
XXXI Convegno Nazionale della Divisione di Chimica Organica della Società Chimica Italiana
Autore/i: V., Fino; P., Bruni; Francescangeli, Oriano; Pisani, Michela
Editore: Università della Calabria
Luogo di pubblicazione: ARCAVACATA DI RENDE
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83375

Ferroelectric response in a fluid nematic phase
Book of Abstracts
Autore/i: Francescangeli, Oriano
Editore: Institute of Physics ,National Academy of Sciences
Luogo di pubblicazione: KIEV
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/47217

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

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

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

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

Vettori Sintetici di DNA per impieghi in terapia genica: sintesi, determinazione strutturale, trasfezione cellulare
Atti del XXXI Convegno Nazionale dela Divisione di Chimica Organica della Società Chimica Italiana
Autore/i: Pisani, Michela; V., Fino; Francescangeli, Oriano; Bruni, Paolo
Editore: Università della Calabria
Luogo di pubblicazione: ARCAVACATA DI RENDE
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83372

Structure and function of self-assembled liposome-DNA-metal complexes for gene transfer
European Synchrotron Radiation Facility Highlights 2006
Autore/i: P., Bruni; Pisani, Michela; A., Amici; C., Marchini; M., Montani; Francescangeli, Oriano
Editore: G. Adams
Classificazione: 2 Contributo in Volume
Abstract: Invited Contribution
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/42226

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

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

Self-assembled ternary complexes of neutral liposomes, DNA and bivalent metal cations for gene delivery
V Convegno Nazionale AICIng
Autore/i: Pisani, Michela; Francescangeli, Oriano; P., Bruni
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83369

Structure and function of self-assembled liposome-DNA-metal complexes for gene transfer
Proceedings of the Fifth International Conference on Synchrotron Radiation in Materials Science SRMS-5,
Autore/i: Francescangeli, Oriano; Pisani, Michela; Bruni, Paolo; C., Marchini; M., Montani; A., Amici
Editore: Argonne National Laboratory
Luogo di pubblicazione: CHICAGO
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51584

Optical and mechanical shrinkage effects in dye-doped photonic bandgap structures based on organic materials
PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Autore/i: Lucchetta, Daniele Eugenio; Francescangeli, Oriano; Criante, Luigino; Simoni, Francesco; Pierantoni, Luca; Rozzi, Tullio; Scoponi, M.; Rossetti, S.
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50093

Self-assembled ternary complexes of neutral liposomes, deoxyribonucleic acid, and bivalent metal cations. Promising vectors for gene transfer?
APPLIED PHYSICS LETTERS
Autore/i: Bruni, Paolo; Pisani, Michela; A., Amici; C., Marchini; M., Montani; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: By means of synchrotron x-ray diffraction we demonstrate the self-assembled formation of the neutral ternary dioleoyl-phosphatidylcholine-deoxyribonucleic acid (plasmid)−Me2+ (Me = Ca and Mn) complexes in the liquid-crystalline Lα phase. We also report an attempt of an in vitro transfection on mouse fibroplast NIH 3T3 cell lines, which shows the capability of these complexes to transfect DNA. Based on the reported results, efficient encapsulation of DNA plasmids in these ternary neutral complexes may represent an important alternative to current systemic gene approaches.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/57642

Structure and Phase Behavior of Self-Assembled DPPC-DNA-Metal Cation Complexes
THE JOURNAL OF PHYSICAL CHEMISTRY. B
Autore/i: Pisani, Michela; Bruni, Paolo; G., Caracciolo; R., Caminiti; Francescangeli, Oriano
Editore: Columbus, OH : American Chemical Society, 1997-
Classificazione: 1 Contributo su Rivista
Abstract: Multilamellar liposomes of dipalmitoylphosphatidylcholine (DPPC) in solution with DNA and bivalent metal cations (Ca2+, Mn2+, Mg2+) self-assemble into a ternary DPPC−DNA−Me2+ complex. The supramolecular structure of the complex consists of an ordered multilamellar assembly where hydrated DNA helices are sandwiched between the lipid bilayers and the metal cations bind the phosphate groups of DNA to the lipid polar heads. In the range of explored incubation times, the complex coexists with the uncomplexed DPPC over the whole temperature range investigated (20−55 °C). Accordingly, two distinct coexisting lamellar phases are observed, one corresponding to the ternary complex and the other to the uncomplexed lipid. The structure and thermotropic phase behavior of both of these have been investigated by means of synchrotron X-ray diffraction, and the relevant structural data are deduced from experimental electron density profiles. While the uncomplexed lipid exhibits the same phase behavior as pure DPPC, that is, Lβ‘−Pβ‘−Lα, the thermotropic behavior of the bound lipid in the complex is partially altered. This is manifested as an increase in the main transition temperature and the disappearance of the ripple phase leading to the single − phase transition. The role of the different metal cations in promoting and stabilizing the DNA condensation into the ternary complex is also discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53216

Studi Strutturali di complessi ternari Lipidi-DNA-ioni metallici
XXIV Congresso TUMA
Autore/i: Pisani, Michela; Francescangeli, Oriano; P., Bruni
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83359

Plastic lasers based on high resolution reflection gratings
Technical Digest, art. no. 1568362
Autore/i: Lucchetta, Daniele Eugenio; L., Criante; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/43539

Fe2+ promoted peroxidation of 1,2-diacyl-sn-glycero-3-phosphocholine liposomes in the presence of calf thymus DNA.
ORGANIC & BIOMOLECULAR CHEMISTRY
Autore/i: Bruni, Paolo; Pisani, Michela; Iacussi, M; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: The peroxidation reaction of some liposomes, namely egg yolk phosphatidylcholine (PC), dioleoyl- (DOPC) and dilinoleoyl- (DLPC) phosphocholines, promoted by ferrous ions (Fenton reaction) has been studied at the physiological pH value, in the absence and in the presence of calf thymus DNA. A catalytic effect of DNA, where the lag time reduces or is completely annihilated, together with an increase in both the yields and the rates of the reactions, has been observed. This effect of DNA has been attributed to the ability of the three components, liposomes, DNA and Fe2+, to form a stable ternary complex, which produces a reduction of the undulatory fluctuations of the hydrocarbon tails of liposomes and strengthens the packing between the acyl chains in the lipid bilayers, with the consequence of enhancing the liposome crystallinity.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52650

Self-assembled liposome-DNA-metal complexes related to DNA delivery
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Pisani, Michela; Bruni, Paolo; Conti, C.; Giorgini, Elisabetta; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: We have carried out a systematic structural study of novel liquid-crystal phases of self-assembled neutral lipid-DNA-metal cation complexes in water solution. Small-angle X-ray scattering experiments have given new insight into the structures of these ternary complexes. We have shown that different divalent metal cations are equally active in promoting the DNA condensation into the ternary complex when different lipid and DNA species are used. In addition, strong indication has been found that the phase of the complexes reflects the structure and symmetry of the parent lipid phase. These achievements provide an important structure-composition correlation that may drive the best design of these materials for future applications as non-viral DNA carriers in gene therapy.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/53121

Light-induced molecular adsorption and reorientation at polyvinylcinnamate-fluorinated/liquid-crystal interface
PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Autore/i: Francescangeli, Oriano; Lucchetti, Liana; Simoni, Francesco; V., Stanic; A., Mazzulla
Classificazione: 1 Contributo su Rivista
Abstract: We have carried out a detailed experimental study, by means of x-ray reflectometry (XRR) and half-leaky guided mode (HLGM) optical characterization, of the light-induced molecular adsorption and reorientation at the polyvinylcinnamate-fluorinated (PVCN-F)/liquid-crystal (LC) interface of a LC cell doped with the azodye methyl red (MR). The XRR data allowed characterizing the microscopic structure of the adsorbed dye layer both before irradiation (dark adsorption) and after irradiation (light-induced adsorption). The HLGM optical characterization has made possible the experimental determination of the nematic director profile in the LC cell and evaluation of the effects of light-induced adsorption on the LC anchoring conditions. The experimental findings have confirmed the formation of a dark-adsorbed layer and are in agreement with the absorption model previously proposed to account for the complex phenomenology related to light-induced anchoring and reorientation in dye-doped liquid crystals.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/52957

Layered ω-Substituted Alkylpyridinium Salts with Inorganic Anions: Effects of H-Bonding Patterns on the Layer Thickness
CRYSTAL GROWTH & DESIGN
Autore/i: F., Neve; Francescangeli, Oriano
Editore: AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, USA, DC, 20036
Classificazione: 1 Contributo su Rivista
Abstract: The synthesis and characterization of a carboxy-substituted alkylpyridinium cation with inorganic counterions is reported. Structural evidence points to the formation of a layered structure with mutual recognition of cations through strong O-(HO)-O-... bonding when halides X- (X = Cl, Br) are chosen. Variation of the anionic component to complex metal ions of [MX4](2-) type affords a different layer motif with weaker cation-anion O-(HX)-X-...-M interactions and interdigitation of functionalized alkyl chains.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29832

Supramolecular Ordering of Self-Assembled Lipid-DNA-Metal Complexes related to gene therapy
8th European Conference on Liquid Crystals
Autore/i: Francescangeli, Oriano; Pisani, Michela; P., Bruni
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83356

Thermotropic mesomorphism in penta- and hepta-coordinated metal complexes
LIQUID CRYSTALS
Autore/i: I., Aiello; M., Ghedini; A., Grisolia; D., Pucci; Francescangeli, Oriano
Editore: Taylor & Francis Limited:Rankine Road, Basingstoke RG24 8PR United Kingdom:011 44 1256 813035, EMAIL: madeline.sims@tandf.co.uk, info@tandf.co.uk, INTERNET: http://www.tandf.co.uk, Fax: 011 44 1256 330245
Classificazione: 1 Contributo su Rivista
Abstract: New Ni(II) and UO2(II) metallomesogens obtained from mesomorphic N,N′-salicyliden(3,3′-diamine-N-methyldipropylamine) ligands containing a pentadentate N3O2 chelating cavity and bearing two or four lateral substituents, are isolated and fully characterized. Some of the synthesized nickel and dioxouranium complexes show a SmC mesophase. To the best of our knowledge, these species are the first pentacoordinated Ni(II) and heptacoordinated UO2(II) metallomesogens to be reported.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/29833

Compact Lasers Based on HPDLC Gratings
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Lucchetta, Daniele Eugenio; L., Criante; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We report the fabrication technique and the main emission properties of two novel all-organic laser devices based on high-resolution reflection gratings written on holographic polymer-dispersed liquid crystal materials by means of conventional holographic techniques. The first type of laser is based upon a distributed Bragg-reflector configuration whereas the second one makes use of a distributed-feedback configuration. Different monomer/liquid-crystal/ photoinitiator mixtures are analysed and the main parameters affecting the grating reflectivity and the overall performances of these plastic mirrorless laser device are discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51767

Supramolecular Ordering of Self-Assembled Lipid-DNA-Metal Complexes probed by X Ray diffraction
6th National Meeting SICL 2004
Autore/i: Francescangeli, Oriano; Pisani, Michela; P., Bruni
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83354

Wavelength flipping in laser emission driven by a switchable holographic grating
APPLIED PHYSICS LETTERS
Autore/i: Lucchetta, Daniele Eugenio; Criante, L.; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We report lasing from a simple wafer structure made of a thin layer of rhodamine 6G as active material and of a switchable holographic mirror, based on a reflection grating made of polymer dispersed liquid crystals. It is shown that switching-off the mirror reflectivity by application of a suitable voltage allows wavelength flipping of the laser emission by 10 nm.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50061

X-ray microdiffraction study of the liquid crystal ordering in confined geometries
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Francescangeli, Oriano; V., Stanic; Lucchetti, Liana; C., Ferrero; M., Burghammer
Classificazione: 1 Contributo su Rivista
Abstract: We report, the results of recent experiments where for the first time X-ray micro-diffraction has been used to probe Liquid crystal ordering and nematic director-field configuration in single micron-sized droplets of polymer-dispersed liquid crystals. The pattern of the bipolar configuration has been detected in a droplet with radius R ≤ 1 μm and the main quantities characterizing the orientational and short-range positional order of the confined nematic have been determined. We report a detailed description of the procedure followed to determine the distribution function of the nematic director in the droplet and the droplet order parameter from the azimuthal intensity profile of the diffraction pattern.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51881

Structure of solid-supported lipid-DNA-metal complexes investigated by energy dispersive X-ray diffraction
CHEMICAL PHYSICS LETTERS
Autore/i: Caracciolo, G; Sadum, C; Caminiti, R; Pisani, Michela; Bruni, Paolo; Francescangeli, Oriano
Classificazione: 1 Contributo su Rivista
Abstract: When mixing aqueous solutions of DNA and dioloeyl-phosphatidylcholine multilamellar liposomes in the presence of Mn 2+ ions, a multilamellar liquid-crystalline phase is formed in which DNA monolayers are comprised between opposing lipid bilayers. Here, we report on a new experimental procedure resulting in the formation of solid-supported DOPC-DNA-Mn 2+ complexes in the biologically relevant excess water condition. The supramolecular structure of solid-supported complexes, characterized by means of Energy Dispersive X-ray Diffraction, exhibits very similar structural properties with respect to the solution structure of the complexes as revealed by synchrotron Small Angle X-ray Scattering measurements.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51766

Susceptobility of dibutyryl chitin and regenerated chitin fibre sto deacylation and depolymerization of lipases
CARBOHYDRATE POLYMERS
Autore/i: Muzzarelli, Raa; Tosi, Giorgio; Francescangeli, Oriano; Muzzarelli, C.
Classificazione: 1 Contributo su Rivista
Abstract: Dibutyryl chitin obtained by esterification with butyric anhydride and regenerated chitin obtained from dibutyryl chitin by saponification, both in the form of wet-spun fibres and non-wovens, were examined by infrared spectrometry and X-ray diffraction spectrometry. Chitin fibres and chitosan fibres were also studied for comparison, and found to maintain the XRD spectral features of the parent chitin and chitosan. On the opposite, DBC fibres and non-woven exhibited depressed crystallinity, the peak at 0.46–0.47 nm, typical of chitin, being hardly detectable, while the one usually at ca. 1.00 nm was present at ca. 1.20 nm. Both DBC fibres and non-woven were highly oriented. When exposed to porcine pancreatic lipase or wheat germ lipase, the DBC fibres gained improved crystallinity with peaks at 1.14–1.18 and 0.41 nm, due to partial regain of chitin structure as a consequence of partial enzymatic removal of butyryl groups, as confirmed by ATRFTIR. The RC fibres exhibited broad XRD peaks at 0.96 and 0.36 nm; sharper peaks at 0.34, 0.46–0.49 and 0.96 were observed after exposure to lipases, due to removal of a disordered polymer fraction susceptible to the unspecific enzymatic depolymerization. In fact the RC fibres were found to have 8% lower degree of acetylation compared to parent chitin, as a consequence of the alkaline regeneration treatment. In conclusion, these modified chitins are scarcely susceptible to degradation by lipases (besides to lysozyme, as already reported in the literature); therefore their biochemical significance in wound management seems limited. They, however, appear to be the ideal textile materials for providing mechanical support to freeze-dried chitosan sponges having amply documented activity in wound healing, and for the preparation of specialty textiles.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51243

“Evidence of an inverted hexagonal phase in self-assembled phospholipid-DNA-metal complexes”
EUROPHYSICS LETTERS
Autore/i: Francescangeli, Oriano; Pisani, Michela; V., Stani; Bruni, Paolo; T. M., Weiss
Editore: EDP Sciences:17 Ave Du Hoggar, BP112, 91944 Les Ulis Cedex A France:011 33 1 69187575, EMAIL: subscribers@edpsciences.com, INTERNET: http://www.edpsciences.com, Fax: 011 33 1 69860678
Classificazione: 1 Contributo su Rivista
Abstract: We report the first observation of an inverted hexagonal phase of phospholipid- DNA-metal complexes. These ternary complexes are formed in a self-assembled manner when water solutions of neutral lipid dioleoylphosphatidylethanolamine (DOPE), DNA and divalent metal cations (Me2+; Me = Fe, Co, Mg, Mn) are mixed, which represents a striking example of supramolecular chemistry. The structure, derived from synchrotron X-ray diffraction, consists of cylindrical DNA strands coated by neutral lipid monolayers and arranged on a two-dimensional hexagonal lattice (Hc II ). Besides the fundamental aspects, DOPE-DNA-Me2+ complexes may be of great interest as efficient nonviral delivery systems in gene therapy applications because of the low inherent cytotoxicity and the potential high transfection efficiency.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/36700

Light amplification by dye-doped holographic polymer dispersed liquid crystals
APPLIED PHYSICS LETTERS
Autore/i: Lucchetta, Daniele Eugenio; L., Criante; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: (selected for June 7, 2004 issue of Virtual Journal of Nanoscale Science & Technology) In this letter we report a “one-step” fabrication technique of an optical active organic photonic band gap (PBG) structure allowing the onset of the amplification spontaneous emission effect and narrowing of the corresponding band. This result has been achieved through the addition of the dye rhodamine 6G to a standard holographic polymer dispersed liquid crystal pre-polymer mixture. The effects of the dye addition on the optical properties of the polymerized PBG structure have been analyzed. The spectra emitted by this optically active periodic structure have been studied as a function of the excitation energy.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51359

Colossal optical nonlinearity in dye-doped liquid crystals
OPTICS COMMUNICATIONS
Autore/i: Lucchetti, Liana; M., DI FABRIZIO; Francescangeli, Oriano; Simoni, Francesco
Classificazione: 1 Contributo su Rivista
Abstract: We report the experimental evidence of a nonlinear optical response among the highest ever observed. A nonlinear refractive index on the order of 103 cm2/W (that is 108 times higher than in Giant Optical Nonlinearity) has been obtained in randomly oriented thin liquid crystal cells. This result shows the fundamental role played by the surface in the nonlinear optical response of dye-doped liquid crystals.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51410

“Liposome-DNA-metal complxes related to DNA delivery”.
20th International Liquid Crystal Conference
Autore/i: Pisani, Michela; Francescangeli, Oriano; Bruni, P.; Giorgini, Elisabetta; Conti, C.
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83352

“Liquid-crystal ordering in confined geometries probed by X-ray microdiffraction"
Congresso Nazionale di Fisica della Materia
Autore/i: Francescangeli, Oriano; C., Ferrero; V., Stanic; Pisani, Michela; Lucchetti, Liana; M., Burghammer
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83347

“Supramolecular structure of self-assembled liposome-DNA-metal complexes”
Congresso Nazionale di Fisica della Materia
Autore/i: Pisani, Michela; V., Stanic; P., Bruni; M., Iacussi; G., Tosi; Francescangeli, Oriano
Classificazione: 4 Contributo in Atti di Convegno (Proceeding)
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/83339

Supramolecular ordering of self-assembled liposome-DNA-metal complexes
Recent Research Developments in Macromolecules
Autore/i: Francescangeli, Oriano; Pisani, Michela; V., Stanic; Bruni, Paolo; M., Iacussi
Editore: Research Signpost
Luogo di pubblicazione: TRIVANDRUM-695 023, KERALA
Classificazione: 2 Contributo in Volume
Abstract: Invited article
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/51663

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

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

X-ray diffraction study of dioleoylphosphatidylcholine-DNA-Mn2+ complexes
MOLECULAR CRYSTALS AND LIQUID CRYSTALS
Autore/i: Francescangeli, Oriano; Stanic, V; Lucchetta, Daniele Eugenio; Bruni, Paolo; Iacussi, M; Cingolani, F.
Classificazione: 1 Contributo su Rivista
Abstract: We have studied the structural properties of the triple complex dioleoylphosphatidylcholine-DNA-Mn2+ by means of synchrotron x-ray diffraction. The data revel a novel multilamellar structure similar to that recently found in cationic liposomes-DNA complexes. ne study of the bilayer undulations suggests that condensation of the DNA within the lipid bilayers reduces the flexibility of the lamellae in the complex and suppresses almost completely the undulatory fluctuations. These complexes are of grate interest for potential applications as synthetically-based nonviral carriers of DNA vectors for gene therapy.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/50764

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