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An expression for screening of the effective monomer interactions in semirigid polymer systems is developed. Anisotropic interactions dependent on monomer orientation are taken into account in an expansion of the bare potential in spherical harmonics. Using the method of Gaussian random fields previously applied to simple flexible polymers, the equation for the screened potential is given as an expansion in the density correlation functions of the effective chain. The effect of the polymer interactions on the persistence length and end-to-end distance of worm-like chains is calculated and shown to be small. [ABSTRACT FROM AUTHOR]

Presents information on a study that discovered that a cholesteric liquid crystal with negative dielectric anisotropy and with a visible wavelength selective reflection presented high memory effects when encapsulated in a polymer film. Experimental procedaure; Results and discussion; Conclusion.

The Frank elastic constants of a polymer liquid crystal are calculated. The effects of chain flexibility and screened orientational interactions are considered. A quadratic dependence in the chain length is shown to occur under certain conditions. [ABSTRACT FROM AUTHOR]

Presents a study that investigated annealing and memory effects in polymer-dispersed chiral liquid crystals. Background on the use of chiral polymer-dispersed droplets for producing switchable color displays; Description of thermal treatment; Effect of annealing on the memory state of the polymer film.

We have studied the influence of polymer network liquid crystal alignment on optical and electro-optical properties. Composite alignment (parallel/homeotropic) was investigated in comparison with symmetric parallel/parallel and homeotropic/homeotropic alignments. The applied voltage leads to a reflective wavelength shift towards low wavelengths according to two modes in the case of symmetric planar alignment. Depending on polymerization conditions, a band broadening can be obtained, but a total reversibility of the optical properties is not recovered after application of a high voltage to the samples. The layer thickness appears to be a fundamental parameter in the case of a hybrid-aligned active layer and a wide band is obtained after measurements (I-V) using increasing voltages. [ABSTRACT FROM AUTHOR]

We consider the realization and the electro-optical behaviour of a polymer network stabilized liquid crystal whose reflection band has been broadened. We particularly emphasize the reflective properties (mean value of the selective reflection and bandwidth, and the parameters of broadening) and their evolution with voltage. Broadband active films can be obtained under special conditions of polymerization. A mechanism concerning the broadening of the reflection band is put forward based on inhomogeneous consumption of a chiral monomer within the samples. [ABSTRACT FROM AUTHOR]

Liquid crystal/polymer network composites with small amounts of photocrosslinkable cholesteric prepolymer are described. Rheological experiments are used to study the evolution of the mechanical properties of the composite material during the UV curing process. The behaviour of the complex shear modulus during the formation of the polymer network leads to a gelation-like description. Corresponding critical exponents have been proposed and discussed in the frame of percolation. [ABSTRACT FROM AUTHOR]

The polymer network-ferroelectric liquid crystal (FLC) microcomposites are prepared by UV crosslinking of a chiral prepolymer diluted in a FLC. A fast cross-linking process involving 20 mW cm[sup -2] UV intensity produces material with ferroelectric properties which have strongly deteriorated compared with the pure FLC. By a slow process using a UV intensity of 2 mW cm[sup -2] the ferroelectric properties are less affected. It is supposed that the very dense polymer network, which arises during the fast process, is responsible for hindering the switching process and decreasing the spontaneous polarization. The photopolymerization kinetics are determined by measuring the switching current during the UV irradiation. The characteristic time of cross-linking is mainly reflected in the evolution of the spontaneous polarization and rotational viscosity with time. [ABSTRACT FROM AUTHOR]

Three kind series of (2-hydroxypropyl)cellulose (HPC) derivatives, the esters (ES), the ethers (ET) and the esters containing fluorocarbon components (FES) were prepared, and the thermal and cholesteric mesophase properties were compared among them. The optical pitch of ES increased with decreasing the degree of substitution (DS). Contrary to ES, the optical pitch of ET decreased with decreasing DS. The cholesteric-isotropic transition temperature of FES exhibited the even-odd oscillation according to the number of carbons in substituent. The reverse optical pitches of ET and FES were larger than that of ES, respectively, at the same temperature and at the same number of carbons in substituent. [ABSTRACT FROM AUTHOR]

The experimental variation of the intrinsic viscosity [η] as a function of temperature for various molecular weights of cellulose tricarbanilate in solution in dioxane displays a S-shaped character with two plateau regions, respectively at low and high temperatures. The use of the Yamakawa model leads to two distinct values for the chain stiffness q, one which may be associated to a rather 'rigid' conformation of the macromolecule (q=139 Å), the other which may correspond to a rather 'flexible' conformation (q = 84Å). [ABSTRACT FROM AUTHOR]

A polarizing microscope is used to investigate the liquid crystalline phase of polynonylisocyanates. The effect of the degree of polymerization of the chains on the anisotropic-isotropic transition temperature is demonstrated and a discussion within the theory of semi-rigid liquid crystalline polymers is given. [ABSTRACT FROM AUTHOR]

Phase diagrams for the isotropic-anisotropic phase transition in solutions of a thermotropic cellulose derivative, hydroxypropyl cellulose are presented. The effect of the molecular weight is demonstrated. A comparison to the theory of semi-rigid liquid crystalline polymers is given. [ABSTRACT FROM AUTHOR]

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