Formation of Percolated Structure During Solvent Casting of Polymer Blend-solvent Systems.

Abstract

The development of phase separation in ternary systems composed of polybutadiene-poly(styrene-co-butadiene)-good solvent was studied by time-resolved light-scattering during the solvent casting process. Double percolated structures with two different periodic distances were observed for the thick film. The structure with the smaller periodic distance was formed at the surface of films and the larger one was formed inside the film. It was found that the periodic distance for the larger percolated structure was proportional to (tP – tS)0.6, where (tP – tS) is the lapse of the time from the start of phase separation to fixation of the structure. The time dependence of the wave number, qm, at which the light-scattering intensity reaches maximum, was correlated by a similar relationship. The intensity of light scattering at qm was proportional to qm3.3 irrespective of the solvent-casting conditions. The development of the percolated structure was qualitatively interpreted by numerical analysis of an equation describing spinodal decomposition and an equation expressing the time dependence of the polymer concentration in the cast solution.