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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]