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

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.