Dimensional Crossover in the Phase Separation Kinetics of Thin Polymer Blend Films

Abstract

The kinetics of phase separation in thin polymer blend films of polystyrene and polybutadiene on a silicon substrate is examined by optical microscopy of the free film boundary. Our observations on 1000 and 200 \AA{} films are consistent with a crossover from three- to two-dimensional spinodal decomposition kinetics in the (off-critical) viscous hydrodynamic regime. In this stage of phase separation the exponent $n$, characterizing the scale $R(t)\ensuremath{\sim}{t}^{n}$ of the coarsening pattern, is predicted to change from 1 to a value near 0.46 upon lowering the dimensionality.