A Test of the Scaling Law for Structure Function in Phase Separation Process of Polystyrene/Poly (methylphenylsiloxane) Liquid Mixtures

Abstract

Structure function S(k, t) in process of phase separation was investigated by light scattering for polystyrene/poly(methylphenylsiloxane) mixtures to test the scaling law for S(k, t) in the late stage. For the critical composition, the structure function obeyed the scaling law of S(k, t)=k_m⁻³·S(k⁄k_m), where k is the wave number, k_m the wave number yielding the maximum intensity, and S(k⁄k_m) the scaled structure function independent of time t. However, S(k, t) for the off-critical composition gradually changed with t, becoming to have a broader peak, so that the scaling law was only approximately satisfied. The full-width at a half of the maximum intensity increased with increasing quench-depth, being almost the same for the critical and off-critical compositions at comparable quench-depths. The value of exponent h in the power law S(k⁄k_m)∝(k⁄k_m)^−h at k⁄k_m>1 was around 4 for the off-critical quench, in agreement with the Furukawa theory, while for the critical quench it was slightly larger than 4, but not as large as the theoretical value 6.