Synthesis, characterization, and dynamics of a rod/sphere composite liquid

The synthesis, characterization, and studies of the dynamics and statics of a new rod/sphere composite liquid are reported here. The composite liquid contains silica spheres and the rigid rod polymer, poly({dollar}gamma{dollar}-benzyl-{dollar}alpha{dollar},L-glutamate) (PBLG), dispersed without aggregation in dimethylformamide. The spheres, of radii 39.4 and 60.4 nm, were synthesized by the method of Stober and coated with 3-(trimethoxysilyl)propyl methacrylate. 102,000, 200,000, and 249,700 g/mol PBLG were used. Dynamic light scattering (DLS) was used to simultaneously measure the translational mutual diffusion constants of both the rods and spheres. This data was compared to that for rod/DMF and sphere/DMF solutions. A DMF/pyridine solvent mixture was found to refractive index match dilute sphere solutions. Total intensity light scattering (TILS) was utilized for polymer characterization and to probe the solution structure.; The 102,000 g/mol rod translational diffusion constants were unchanged by the presence of dilute concentrations of spheres. Two dynamical regimes were observed for the rod diffusion. The transition between these regimes was attributed to the change from dilute to semidilute dynamics.; Five composite liquids were studied in which the sphere size, rod length, and rod concentration were varied. Microviscosities ({dollar}etamu{dollar}) as low as 1/2 of the solution viscosity ({dollar}eta{dollar}) were determined from the sphere diffusion constants. At low rod concentrations, the microviscosities qualitatively follow the Langevin and Rondelez equation which depicts the solution as a net in which sphere diffusion is critically dependent on the ratio of sphere radius to polymer mesh size. At higher rod concentrations, microviscosities at least 20% lower than the solution viscosity were measured for all but the solution containing the smallest rods. A comparison of the DLS and TILS data suggests the solution structure starts changing at these high (but prenematic) rod concentrations.; The sphere diffusion constants were fit to: D/D{dollar}sb0{dollar} = exp({dollar}-alpha csp{lcub}nu{rcub}{dollar}). The c{dollar}spnu{dollar} dependence (0.77 {dollar}leq nu leq 0.92{dollar}) is comparable to experimental results on sphere/coil solutions, but not to theories which predict {dollar}nu{dollar} = 0.5. The poorest fits occur when {dollar}etasbmu{dollar}/{dollar}eta{dollar} is the smallest.