OPTICAL-PROPERTIES OF STRETCHED POLYMER-DISPERSED LIQUID-CRYSTAL FILMS

The basic mechanisms determining the formation of optical anisotropy i n stretched, thin polymer dispersed liquid crystal (PDLC) films with m icron sized nematic droplets have been studied experimentally and the results analysed in terms of a proposed theoretical model. The experim ents were performed on PDLC films with the bipolar nematic director co nfiguration in the droplets, where the film transmittance, microscopic structure, and birefringence of the polymer matrix were studied. It i s shown that the orientational ordering of bipolar nematic droplets, i ntroducing the main contribution to the ability of stretched PDLC film to polarize the transmitted light, is strongly dependent upon initial droplet shape and the elastic properties of the polymer matrix. The ' anomalous' nematic director orientation is also observed in a portion of elongated droplets where the axes of bipolar configurations do not coincide with the major axes of the droplet cavities due to the presen ce of inclusions at the cavity walls. The effect of alternation of dro plet size and shape upon stretching and the influence of optical aniso tropy of the polymer matrix on film transmittance are analysed. On the basis of the results obtained, simple criteria for optimization of ma in PDLC polarizer performance are formulated.