ON PINNING DOMAIN GROWTH IN 2-PHASE POLYMER LIQUIDS

What has been reported as ''pinning'' or severely reduced growth rates of phase-separated domains in off-critical polymer blends is shown to be the normal effect of crossover between two kinetic regimes associa ted with morphology of the liquid-liquid system. The bicontinuous liqu id microstructure formed by spinodal decomposition grows rapidly by hy drodynamic coarsening where size <(xi)over bar> similar to Lt until th e percolated system dissociates into droplets. The droplets then grow by classical coarsening with radius increasing as (r) over bar(3) simi lar to Kt, where K may be calculated for Ostwald ripening and/or coale scence with no impediments to mobility at any size scale. Apparent pin ning persists for the induction period Delta t approximate to (r) over bar 3/K required for the slower particle growth to be observed, and t he characteristic (r) over bar proportional to t(1/3) behavior is not recovered for approximately 10 Delta t. Numerical simulations of spino dal decomposition in polymer blends, which to date omit hydrodynamics, are unable to capture the change in growth mechanism and rate on snit ching from percolated to droplet morphology.