Late stage spinodal decomposition of a binary polymer mixture. I. Critical test of dynamical scaling on scattering function

Abstract

Unmixing kinetics of quenched critical polymer mixture of polystyrene and poly(vinyl methyl ether) was investigated by time-resolved light scattering technique. In the late stage of spinodal decomposition τ>60, τ being a reduced time, a simple dynamic scaling law was found on the scattering function I(q,t); I(q,t)∼ξ(t)3S̃[qξ(t)] with ξ(t)∼ta, where q is the scattering vector and ξ(t)=q−1m(t) is the correlation length of the periodic unmixed structure at time t which is measured by the position qm(t) of the scattering maximum at time t. The universal scaling functions (or the scaled structure function) F[qξ(t)] experimentally determined from the scattering functions for the lower quench depths (i.e., unmixing at 96.8, 97.3, and 98.2 °C, the spinodal temperature Ts being 95.8 °C) are in good agreement with that predicted by Furukawa, S̃(x)∼x2/(3+x8) for the critical mixtures (percolation regimes) in three dimensions [x=qξ(t)], although the scaling functions F(x) experimentally determined for the higher quench depths (i.e., unmixing at 102.5 and 106.8 °C) are much broader than the predicted function. Thus the decomposition of the polymer mixtures is proposed to obey universality found for metallic alloys, inorganic glasses, and small-molecular liquids in that the decomposed structures obtained at different time scale in the late stage has the self-similarity and unmixing dynamics is scaled with a single length parameter ξ(t).