Percolation of Phase-Separating Polymer Mixtures

We study the percolation problem in a binary phase-separating polymer mixture. By well-designed experiments, we can delineate the percolation line on the phase diagram with sufficient accuracy. Our experiments show that the percolation thresholds start from the random percolation limit (Φ ∼ 0.15) located near spinodal point at T → T_c and then converge toward the geometric coalescence limit (Φ ∼ 0.36) with an increase in the quench depth. This apparent percolation difficulty comes about largely from the Rayleigh instability accompanied by large-amplitude, short-wavelength fluctuations during the spinodal decomposition at deeper quench depth. As a result, the broken "rigid" domains tend to pack closely, and the so-called droplet spinodal decomposition occurs. On the other hand, we observe that, between the selectively attractive walls, the surface-drying percolating phase will break up into droplets prematurely, thereby shifting its percolation line rather considerably. To our knowledge, such an effect is not yet predicted by theory or simulation.