Influence of Mechanical Deformation on Electro-Optical Birefringence in Polymer Networks
A theory of the Kerr effect (electro-optical birefringence) for polymer networks has been developed. The optical birefringence of polymers in the external electric field E is connected with orientation of optically anisotropic chain segments. The orientation of the segment due to induced dipole moment has been considered. The polarizability tensor of segment was assumed to be axial symmetrical with respect to axis of segment. The comparison of electro-optical properties of isotropic polymer networks with those of mechanically deformed networks has been made. The uniaxial mechanical deformed samples (both stretched and compressed) have been considered. Our theory corresponds to an experiment when the boundaries of the deformed sample are fixed so that the volume and the form of the sample remain constant after applying of the electric field (electrostriction effect is not taken into account). The particular case, when external electric field is directed parallel to the direction of mechanical deformation, has been studied.