Dielectric property-electrooptical effect relationships of polymer/liquid-crystal composite films

Abstract

The dielectric properties of a polymer/liquid-crystal (LC) composite film and their influence on the electrooptical response have been investigated. The composite film in which an LC material is embedded as a continuous phase in a three-dimensional spongy polymer matrix shows an electrooptical effect based on a novel concept of light scattering. The electrooptical response speed for the composite film is proportional to ~AeE3, where Ac is the dielectric anisotropy of the LC, and E is the electric field. The dielectric properties of the composite film are approximately explained by the series-connected dielectric composite model consisting of the polymer matrix and the LC phases. Since the magnitude of the ratio of the dielectric constants of both polymer and LC phases, t'p/«'lc. is not always the same as that of the electric conductivities, o-p/o-LC, the magnitude of an ac electric field in the LC phase is modulated and depends on the frequency of the externally applied ac electric field. Further, the frequency dependence of the magnitude of an ac electric field in the LC domain is calculated on the basis of the series-connected dielectric composite model. The calculated result explains qualitatively the frequency dependence of the electrooptical response rise time for the composite film. Also, it is concluded, from the dielectric model calculation, that the electrooptical response rise speed in a wide frequency range of electric field could be improved by using a polymer matrix with greater magnitudes of both electric conductivity and dielectric constant.

Component Dependence of Aggregation Structure and Light Scattering Properties of Polymer/Liquid Crystal Composite Films

“…26, No. 8,1994 of them are same. If the light scattering of the composite film upon an electric field -OFF state only depends on the mismatch between nv and refractive index of LC, the lower transmittance (0%) of the composite film (C) than that (7%) of the composite film (B) means that the composite film (C) has the much more light scattering points between matrix polymer and LC than those of the composite film (B), because their components, polymer and LC are same.…”

“…26, No. 8,1994 properties of the composite films shown in Figure 8 upon electric field -ON and -OFF states. The composite film (C-1) and (C) showed same transmittance (almost 1 %) upon an electric field -OFF state.…”

“…8 -10 And the distortion of nematic directors in the LC channels is strongly dependent on the aggregation structure of the composite film. The aggregation structure of the composite film strongly depends on the components ratio 8 ' 11 > and the solvent evaporation velocity during the film preparation process. 12 > Therefore, studies on the relationships between aggregation structure and light scattering properties of the composite film are important to establish the mechanism of light scattering in the composite film.…”

Morphological Studies on Polymer/Liquid Crystal Blend.

“…Blends of low molecular-weight liquid crystals (LC) with polymers have been extensively studied (1)(2)(3)(4)(5), because such mixtures are expected to be useful as materials for electro-optical applications. Many studies have been reported on the phase behavior of blends of LC with flexible-chain polymers, such as poly(ethylene oxide) (3)(4)(5), polystyrene (3)(4)(5), and poly(methyl methacrylate) ( 5 ).…”

Control of Phase-Separated Structure in (Polymer/Liquid Crystal) Composite Films and Their Electro-Optical Switching Characteristics

“…8 -i 9 The light scattering state is dependent on optical heterogeneties in the composite film, such as a spatial distortion of nematic directors and/or mismatching in refractive indices of the components. 15 Consequently, the light scattering and light transmission switching properties of the composite film are decisively influenced by the phase separated structure in the composite film. It is, therefore, necessary to study the phase separation mechanism during the solvent evaporation to control the phase-separated structure of the composite film.…”