A NEUTRON-SCATTERING STUDY OF THE ORIENTATION OF A LIQUID-CRYSTALLINEPOLYMER BY SHEAR-FLOW

The orientational response of a liquid crystalline polymer (LCP) solut ion, specifically poly(benzyl L-glutamate) (PBLG) in deuterated benzyl alcohol, to the application of a sheat field has been determined by i n-situ neutron scattering. By analyzing the anisotropic two-dimensiona l scattering pattern, the orientation of the LCP at different shear ra tes, gamma, in the now-vorticity plane was determined. It was found th at the LCP response has three regimes. At low sheat rates, gamma < gam ma(1), the orientation of the LCP molecule increases with gamma, at in termediate flow rates, gamma(1) < gamma < gamma(2), there is not much change in the orientation of the PBLG molecule with gamma, and at high gamma, gamma > gamma(2), there is again an increase in the orientatio n of the LCP with shear rate. The crossover shear rates, gamma(1), and gamma(2), have been shown to correlate well to the first two relaxati on times of a rodlike polymer in concentrated solution. The results ar e also compared and contrasted to some recent studies of the theology of LCP in solution.