PINNING IN PHASE-SEPARATING SYSTEMS

We study a dynamical model of a system with two disparate;energy scales, and focus on the kinetics of phase separation. In this model, nearest-neighbor monomers can interact with one of two quite distinct energies,thereby describing a system with, e.g., van der Waals and hydrogen bond interactions. While the model has been described by an effective Ising model in equilibrium, the nonequilibrium dynamics of phase separation have never-been explored. Here we use Monte Carlo computer simulations of spinodal decomposition to show that the model exhibits ''pinning'' of the structure factor, a behavior also seen in phase-separating polymer-gels and binary alloys with impurities. The rate of strong bond formation depends on an entropic parameter Omega, and we find both the pinned domain size and the crossover time between ''normal'' spinodal decomposition and the pinning scale with Omega as power laws with exponents that relate simply;to the usual growth exponent. We propose a specific mechanism for pinning that permits the prediction of exact values for the pinning exponents. Finally, we discuss applications of the model to binary alloys with quenched disorder and polymer gels.