DYNAMIC LIGHT-SCATTERING FROM A SEMIFLEXIBLE POLYMER AT VERY LOW CONCENTRATIONS

Dynamic light scattering measurements on semiflexible poly(gamma-benzyl-alpha,L-glutamate) have been performed at very low concentrations. near the limit for reliable multiangle detection, in N,N-dimethylformamide. By several methods of data analysis, the mutual diffusion coefficient D(m) is initially level or slightly decreasing with polymer concentration. It then increases substantially, as expected in a good solvent. Static light scattering measurements offer no thermodynamic explanation for the initially level or decreasing behavior, which is apparently a manifestation of the decrease in lateral mobility as the rods become entangled in semidilute solutions. The coefficient C describing the dependence of the first cumulant of the electric field autocorrelation function upon squared scattering vector decreases with concentration, even in the most dilute regime measured. The reliability of persistence lengths estimated for this polymer by dynamic light scattering is considered.