Static and dynamic light scattering of a critical polydisperse polymer solution

The critical behavior of a polydisperse polystyrene solution was investigated using static and dynamic light scattering, focusing on the effect of the polydispersity of molecular weight. The critical exponents for the osmotic compressibility gamma' and the long-range correlation length v' agreed well with our previous results obtained by turbidity measurements, supporting the validity of Fisher's renormalized Ising model for the polydisperse systems. The decay rate distribution function determined from the Laplace inversion of the correlation function reflected the original molecular weight distribution distant from the critical point and the critical fluctuation near the critical point. It was dominated increasingly by the slower mode when approaching the critical point. This behavior was clarified further in a solution having bimodal distribution. The critical behavior of the averaged diffusion coefficient agreed asymptotically with Kawasaki's mode-coupling theory.