Critical dynamics of binary polymer mixtures

Abstract

Mode coupling corrections to the thermal decay rate of binary polymer mixtures near a critical point are investigated. It is found that the classical (Van Hove) theory due to Binder breaks down in several limiting cases. In the regime q R≪1 and qξ≫1, where q is the scattering wave vector, R is the radius of gyration of a chain, and ξ is the correlation length, we find that the classical theory fails when q R≪N e /N 3 / 2. Here N is the number of segments on a chain and N e is the number of segments between entanglements. In the regime q R≪1 and qξ≪1, we find a breakdown in the classical theory when ξ≫R N 3 / 2/N e . The thermal decay rate is predicted to vary like q 3 and q 2/ξ in these two new regimes, respectively. Particularly in the case of polymer mixtures below their entanglement molecular weight we expect to see the mode coupling corrections in light scattering experiments.