SPINODAL DECOMPOSITION IN A POLYMER-SOLUTION

The spinodal decomposition in a critical mixture of polydimethylsiloxane-diethyl carbonate was investigated by a time-resolved light-scattering technique, focusing especially on the early and the intermediate stages of phase separation. The most essential characteristics of this system are that both the refractive index and the density of the solvent and of the polymer are almost the same, and the effects of multiple scattering and sedimentation are mostly eliminated. The exponential growth of the scattered light intensity without changing of its wave number was clearly observed, in good agreement with Cahn-Hilliard theory. The second peak, adding to the main (most dominant) peak, was found in the higher-scattering-angle region in the spectrum, characteristic of the intermediate stage. The scaled time dependences of the wave numbers of both peaks are well represented, respectively, by a master curve for various quenching depths by use of the characteristic wave number and time determined from the time dependence of the scattered light intensity at the early stage of spinodal decomposition. The quench depth dependence of the interdiffusion coefficient and of the wave number, where the most dominant fluctuation grows first in the unstable region, are in good agreement with three-dimensional Ising-model values, indicating the validity of the symmetric law of critical-point universality.