Birefringence, x-ray scattering, and neutron scattering measurements of molecular orientation in sheared liquid crystal polymer solutions

Recent studies of molecular orientation in sheared liquid crystalline polymers have often yielded contradictory results. To check the self-consistency of methods for quantitative measurements of molecular orientation, liquid crystalline solutions of (hydroxypropyl)cellulose [HPC] and poly(benzyl glutamate) [PBG] have been studied using flow birefringence, X-ray scattering, and neutron scattering. HPC X-ray scattering patterns show an arclike pattern with a distinct peak as a function of scattering vector, while PBG patterns show a more diffuse equitorial streak. These differences are attributed to more strongly correlated lateral packing in HPC solutions due to their higher concentration. Measurements of orientation in steady shear flow agree well among the three techniques. Lyotropic HPC and PBG solutions differ in orientation at low shear rates. HPC solutions exhibit near zero orientation at low rates, while X-ray and neutron scattering measurements confirm previous birefringence data showing a low shea...