Late stage spinodal decomposition of a binary polymer mixture. II. Scaling analyses on Q m(τ) and I m(τ)

Abstract

The early-to-late stage of the spinodal decomposition (SD) of the critical mixtures of polystyrene and poly(vinyl methyl ether) was investigated by the time-resolved light scattering technique. The early stage SD where the time evolution of the fluctuations can be described, at least with a good approximation, by the linearized theory of Cahn was found to exist in the reduced time scale τ approximately less than 2. The later stage unmixing process (τ>2) was found to give the scaling laws on the reduced wave number of the dominant Fourier component of the fluctuations Qm and on the reduced maximum scattered intensity Ĩm as given by Qm∼τ−α and Ĩm∼τ β over narrow time scales. In the intermediate stage (2<τ<60), the inequality of β>3α was found, indicating that both the wavelength and amplitude of the dominant mode of fluctuations grow with time. In the late stage (60≲τ), the scaling relation of β=3α was found and dynamical scaling relation was found on the scattering function, indicating that there exists the self-similarity between the structures developed at different times, and the unmixing kinetics is scaled with a single length parameter ξ(t). The experimental behavior of Qm(τ) was compared with those predicted by some theoretical models, and some unique features of unmixing kinetics of polymer (‘‘polymer effect’’) were suggested to arise from entanglements of the long chain molecules.