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Polymer-Dispersed Cholesteric Liquid Crystals(PDCLC)have been obtained using different cholesteric liquid crystals mixtures by the Photopolymerization-Induced Phase Separation method. PDCLC samples of different thickness and different LC concentrations have been studied. The selective reflection spectra for different voltages have shown maximum reflectivity in the infrared region.

We have investigated the behavior of a cholesteric mixture, consisting of the negative dielectric anisotropy liquid crystal MBBA and a chiral dopant S811(1%b.w.). In the phase diagram a.c. applied voltage versus confinement ratio, in addition to the transition previously observed, before reaching the domain of the transition TIC(Translationnary Invariant Cholesteric)–modulated TIC, we have observed a new stability domain for the topological bubble. These bubbles are now surrounded by the TIC domains and necessarily associated to an hyperbolic − 1 defect of the in plane director component.We have also obtained experimentally topological defect chains, formed by topological dipoles similar to the ones formed in 2 compound materials: liquid crystal/solid spheres or liquid crystal/liquid droplets.

A thermally stimulated current investigation has been carried out on a polybutadiene liquid crystal side chain polymer, in order to study the dielectric relaxation of both main and side chains. Two TSC peaks have been found showing the existence of motions of the backbone and reorientations of the mesogenic units.

A new method to synthesize comb-like polymeric liquid crystals with flexible main chains through the chemical modification of a low molecular weight polybutadiene is described. Polarized light optical microscopy and differential scanning calorimetry allow the mesophases to be identified as SA and their existence temperature range to be determined.

We have investigated the response behavior of the thermotropic nematic polymer, DDA-9, in an electric field. DDA-9 is composed of regularly alternating moieties and flexible spacers. At a critical threshold voltage, dependent on molar mass, these polymers show the onset of instability. The appearance of a (non-fluctuating) striped pattern (Williams domains) is shown and the time of formation and relaxation of these patterns is investigated as a function of applied Voltage.

An aromatic polyester of monomeric units similar to PAA separated by flexible spacers show electrohydrodynamic instabilities in external electric field. As in the case of small molecule liquid crystals, conductive and dielectric modes are observed using polarizing microscopy. Slow kinetics due to the higher viscosity allow the observation of the evolution to turbulence. A new periodic texture in the dielectric domain with a frequency dependent periodicity is also observed in polymeric samples The Freedericksz transition in the case of homeotropic anchorage is discussed.

A new kind of side-chains mesomorphic polymers is described, allowing variation of spacer length and degree of substitution. Differential scanning calorimetry and polarising microscopy allow the measurement of the mesophase spread and observation of characteristic textures. A large biphasic gap is observed between isotropic and anisotropic phases. This phenomenon might be due to differences in the substitution degree and tacticity of the samples. In the case of some small molecules liquid crystal-polymer blends, a segregation of the various components also induces a new phenomenon, i.e., a “pseudo reentrant” smectic phase in the biphase. Other properties of this polymer in cyanobiphenyls solutions are described such as the influence of the degree of substitution, spacer length, and low molar mass liquid crystal tail length, on phase diagrams.

A side chain, mesomorphic polymer has been synthesized, starting from a commercial polybutadiene main chain. A preliminary X-ray diffraction study shows the influence of the degree of substitution and the spacer length on the interdigited SA layer thickness, particularly for strongly polar alkoxycyanobiphenyl mesogens. Some hypotheses are deduced about the particular odd-even effect observed with this backbone and on the conformation of the main and side chains.

The cholesteric pitch P of lyotropic mesophases of hydroxypropyl-cellulose are determined from optical measurements, i.e., angular dependence of the scattered light intensity and transmission spectra. The observed results are explained with help of Pincus’ theory for cholesteric liquid crystals. The variations of the twisting power with physical parameters such as polymer concentration C, nature of solvent, molecular weight, and ageing are investigated. The power law P = P oC−α is well satisfied for all polymer solvent combinations. It is proposed that the solvent could influence the cholesteric pitch not only through its intrinsic properties, but also through modifications of the macromolecular characteristics themselves.

The rheological behavior of solutions of cellulose derivatives, acetate, and hydroxypropyl was studied as a function of different parameters; molecular weight, concentration,…, at T = 25°C in the vicinity of the liquid crystal phase transition. A variation of the strain rate sensitivity parameter with concentration is found. A degradation of the solution in trifluoroacetic acid is demonstrated.

After unwinding a cholesteric solution of a mesomorphic polymer by shear, we investigate the evolution of the refractive index. Two mechanisms with different time constants are observed, one corresponding to the cholesteric rewinding, the other to the reorientation of the cholesteric axes.

Electrohydrodynamic instabilities have been studied in an aromatic polyester. Several modes are observed as a function of several parameters such as the frequency of the applied field and the type of surface anchorage. Although similarities to the behaviour of small molecule liquid crystals were found, there are new effects associated with the high viscosity of polymeric samples. The influences of the molecular weight and of the concentration in the polymer liquid crystal/conventional liquid crystal solution are discussed.

Polymer solutions and blends have been extensively studied,motivation being both the fundamental and technological interest1,2. When one component is a liquid crystal polymer, synergy could produce exceptional properties due to the anisotropy of the mesomorphic polymer. It is important to determine the conditions for the existence of either a uniform, mesomorphic phase or an incompatible biphasic system. In such studies, the rigid or semi-rigid character of the chains and the anisotropic interaction between the chains play a role. The presence of mesomorphic macromolecules is “labeled” by their ability to align under certain conditions, a fact which can be exploited in the experimental determination of phase diagrams.

Intravenous administration of methylphenidate hydrochloride, a central stimulant, was unexpectedly found to exert a potent analgesic effect on primary sensory symptoms in a group of patients with Parkinson's disease. This effect, which has now been studied in a short-term, double-blind, placebo-controlled experiment, subsequently disappeared if patients were pretreated with a beta-blocker or with a serotonin antagonist. Cerebrospinal fluid monoamine metabolites were determined in some of these patients, and the 5-hydroxyindoleacetic acid level was found to be significantly lower than in parkinsonian patients without pain and in normal volunteers. Given the mechanism of action of methylphenidate on the central nervous system, the adrenergic and serotoninergic mediation of its analgesic effect, and the demonstration of impaired central serotonin metabolism in the patient group, it is concluded that not only central dopaminergic deficiency but also altered noradrenergic and serotoninergic transmission in the spinal cord are quite likely to play a role in the pathophysiology of pain in Parkinson's disease.