Effect of polymer network structure on electro-optical properties of (polymer liquid crystal) composite films

Methods to control the polymer network structure were investigated for the polymer/liquid crystal composite films prepared by a solvent cast from a homogeneous solution. The polymer network structure was controlled via the intermolecular interaction between matrix polymer and solvent. Composite film prepared from a mixed solution including a small amount of non-solvent for the matrix polymer gave polymer network structure without fine fibrils evidenced from morphological observations by scanning electron microscopy (SEM). The control mechanism of the polymer network structure for the composite film has been studied by evaluating the time-resolved light transmittance and light scattering patterns during film formation. The morphology of the polymer network in the composite film was strongly related to the mutual solubility of solvent and matrix polymer. The electro-optical properties of the composite films directly depended on the morphology of the polymer network. The formation of the phase-separated structure consisting of large LC channels and three-dimensional polymer network structure without fine fibrils was suitable to achieve an electro-optical switching driven by a low electric voltage in the composite film.