The generation and relaxation of structure in polymer liquid crystals under shear flow

The generation and relaxation of molecular orientation in liquid crystalline polymers and the corresponding superstructures have been studied. The degree of molecular orientation which can be generated in polymer liquid crystal systems is determined by the ability to break down domains. To achieve high levels of molecular orientation, domains must be broken down. In wholly anisotropic HPC/water solutions, domains are broken down and much higher levels of flow birefringence are acheived. These conclusions are experimentally supported by the steady state birefringence versus shear rate data reaching a limiting asymptote. Fibrillar structures on the order of 500 nm are believed responsible for the SALS streak perpendicular to the flow direction and the high levels of form birefringence. Surface interactions are believed to result in nonuniform orientation. The surface layer is more easily oriented than the bulk and this orientation in the flow direction leads to a decrease in viscosity. Thus, the viscosity would vary with the distance from the wall. This leads to a nonlinear flow profile in drag flow between parallel plates.