FORMATION OF PERCOLATED STRUCTURE DURING SOLVENT CASTING OF POLYMER BLEND-SOLVENT SYSTEMS

The development of phase separation in ternary systems composed of pol ybutadiene-poly (styrene-cobutadiene)-good solvent was studied by time -resolved light-scattering during the solvent casting process. Double percolated structures with two different periodic distances were obser ved for the thick film. The structure with the smaller periodic distan ce was formed at the surface of films and the larger one was formed in side the film. It was found that the periodic distance for the larger percolated structure was proportional to (tp-t(S))(0.6), where (tp-t(S )) is the lapse of the time from the start of phase separation to fixa tion of the structure. The time dependence of the wave number, q(m), a t which the light-scattering intensity reaches maximum, was correlated by a similar relationship. The intensity of light scattering at q, wa s proportional to q(m)(3.3) irrespective of the solvent-casting condit ions. The development of the percolated structure was qualitatively in terpreted by numerical analysis of an equation describing spinodal dec omposition and an equation expressing the time dependence of the polym er concentration in the east solution.