AN INVESTIGATION OF THE MICROSTRUCTURE OF A ROD SPHERE COMPOSITE LIQUID

Five composite liquids consisting of the rigid rod polymer poly(gamma-benzyl alpha,L-glutamate) and narrowly dispersed, spherical silica particles were studied in the solvent dimethylformamide by dynamic (DLS) and total intensity (TILS) light scattering. The diffusion constant of the spheres was measured by DLS. The effects of sphere size, rod length, and rod concentration on the diffusion of the spheres were investigated to probe the rod solution microstructure. Microviscosities as low as one-half of the solution viscosity were determined from the sphere diffusion constants near the rod concentration c*, which marks the onset of semidilute dynamics. At low rod concentrations, the microviscosities qualitatively follow the equation of Langevin and Rondelez,18 indicating the solution behaves as a net rather than as a continuum. A key parameter in predicting how the spheres diffuse is the ratio of the sphere radius to the polymer mesh size (R/xi). At higher rod concentrations, microviscosities at least 20 % lower than the solution viscosity were measured for all but one composite liquid. The DLS and TILS data suggest the solution structure begins to become inhomogeneous at these higher, but prenematic, rod concentrations and that the rod solution microstructure is important in affecting sphere diffusion in this composite liquid at both low and high rod concentrations.