Phase separation morphology of spin-coated polymer blend thin films

We present the results of a study of the morphology of phase separation in thin films of two different polymer blend systems: polystyrene/polyisoprene and polystyrene/poly(methyl methacrylate). For each blend system, the two polymer components are dissolved in a common solvent. Spin coating of the ternary solutions (polymer blend/solvent) is used to confine the blends to a thin film geometry and to produce phase separation because of rapid evaporation of the solvent (solvent quench). As a quantitative measure of the phase separation morphology the average domain area of the minority component is measured as a function of the polystyrene mass fraction. For both blend systems we identify a small range of composition corresponding to a large increase in the average domain area. We show that the strong dependence of the average domain area on spin speed allows control over the quench time of the polymer blend thin films.