DIELECTRIC PROPERTY ELECTROOPTICAL EFFECT RELATIONSHIPS OF POLYMER LIQUID-CRYSTAL COMPOSITE FILMS

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 approximately DELTA-epsilon-E2, where DELTA-epsilon 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, epsilon'-P/epsilon'-LC, is not always the same as that of the electric conductivities, sigma-P/sigma-LC, the magnitude of an ac electric field in the LC phase is modulated and depends on the frequency of the extrenally 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.