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The thermotropic and optical characterisations of a novel polymer dispersed liquid crystal (PDLC) system based on polysulfone UDEL P-1700 as polymer matrix and a low molecular weight liquid crystal compound containing a mesogenic azomethine core and a cyano-substituent were investigated. The PDLC samples were prepared by solvent-induced phase separation (SIPS) and thermally induced phase separation (TIPS) methods using various compositions in the two components. Information on the morphology and phase structure was obtained by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurements. PDLC systems with well-defined droplets were obtained for the composite with medium content of liquid crystal compound. The optical characterisation of these materials was performed by analysing their UV-visible absorption and photoluminescence emission as a function of the liquid crystal aggregation degree. [ABSTRACT FROM AUTHOR]

The paper deals with the study of the thermotropic liquid crystalline properties of a new azomethinic symmetric dimer and some of its structural heterogeneous mixtures with one of its reagents. Their thermotropic behaviour was monitored by polarised light microscopy, differential scanning microscopy and variable temperature X-ray diffraction measurements. The influence of the structural heterogeneity on the mesomorphic behaviour was established and some similarities with the mesomorphic behaviour of the polydisperse polymers were underlined. [ABSTRACT FROM AUTHOR]

Azomethine liquid crystals (LCs), constituted by symmetric and asymmetric bithiophene or fluorene units as chromophores, were designed and synthesised. Their thermotropic behaviour was investigated using optical microscopy, differential scanning calorimetry, and wide angle X-ray diffraction. A lowering of transition temperatures was obtained by the introduction of the lateral methyl group as compared with unsubstituted compounds. The observed LC phases possess the classical textures of calamitic LCs. The optical properties of the target compounds were evaluated, both in solution and in solid state. A blue fluorescence was observed for fluorene containing compounds and a green fluorescence was observed for analogous bithiophene containing compounds. The introduction of a methyl lateral group onto the aromatic rings led to a remarkable increase in the solution emission properties. [ABSTRACT FROM AUTHOR]

A new series of thermotropic polyazomethines (PAMs) containing flexible spacers in the main chain and side methoxy groups on the mesogenic core has been synthesised by solution polycondensation reaction ofo-dianisidine withα,ω-bis(4-formylphenoxy)-alkanes. A model compound was also synthesised by condensation reaction ofo-dianisidine withp-butoxybenzaldehyde, in order to accomplish the structural characterisation and for a better understanding of the polymer properties. Chemical structure of the studied polymers was confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy, and the supramolecular organisation was determined by powder wide angle X-ray diffraction measurements. The thermal properties of the polymers and model compound were investigated by thermogravimetry, polarised light microscopy and differential scanning calorimetry. The resulting data indicated high thermostability without significant weight loss up to 380°C and nematic liquid crystalline behaviour with large stability range (around 100°C) of the mesophase. Electronic UV–Vis absorption and light emitting ability were also investigated; these PAMs presented broad emission bands in the blue domain. [ABSTRACT FROM AUTHOR]

Polymer-dispersed liquid crystal (PDLC) systems based on polysulfone as carrying matrix and 4-cyano-4ʹ-pentylbiphenyl (5CB) liquid crystal (LC) were obtained as thin transparent films. The PDLC films were prepared by solvent- and thermally induced phase separation methods, with various compositions in the two components. Information on the phase separation was obtained by polarised light optical microscopy, differential scanning calorimetry and scanning electron microscopy. The PDLC composites show well-defined droplets of submicrometric size, around 650 nm for a medium content of LC and around 250 nm for a low one. The droplets show a radial configuration and a homeotropic alignment of the LC molecules within. By contact angle measurement and surface free energy calculations, it was established that self-assembling of aliphatic units of the two composite components, at droplet interface, is the driving force of the homeotropic alignment. Moreover, these data indicated the potential biocompatibility of the studied composites. The photophysical behaviour shows a better light emission of the PDLCs containing bigger droplets. [ABSTRACT FROM PUBLISHER]

Polymer dispersed liquid crystal (PDLC) systems based on a smectic liquid crystal embedded in polyvinylalcohol-boric acid (PVAB) as biocompatible carrying matrix were prepared and characterised. The smectic liquid crystal contains biologically friendly structural blocks and was designed to have a direct isotropic–smectic transition and a mesophase stability range at human body temperature. The resulted PDLCs were characterised from morphological and thermotropic aspects by polarised light microscopy (POM), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and Raman microspectroscopy, and their surface properties were determined by contact angle measurements and surface energy calculations. It was concluded that the electron-deficient PVAB matrix constrains the ester liquid crystal to grow as spherical droplets with planar anchoring. The droplet diameter was comprised in the range 4–11 µm, with a predominant droplet population around 7 µm and a narrower polydispersity as the amount of the liquid crystal in the polymeric matrix increases. The resulted PDLC films exhibited versatile morphology and surface properties which allow targeting of their application. [ABSTRACT FROM PUBLISHER]

Novel semiflexible polyazomethines containing chromophoric units into azomethine mesogenic core have been synthesised by condensation of a flexible dialdehyde with mesogenic diamines containing fluorene, antraquinone, pyrimidine, azobenzene and benzophenone. The thermotropic behaviour of the resulting polyazomethines was assessed by differential scanning calorimetry, polarised light microscopy and investigations of the miscibility relations. While the pure polyazomethines showed a birefringent viscous texture difficult to be ascribed, by mixing with a liquid crystal dimer, clear Schlieren or marbled textures were observed, indicating a nematic mesophase. The polymers exhibited violet, blue or yellow light emission. [ABSTRACT FROM AUTHOR]