Filler-induced composition waves in phase-separating polymer blends

The influence of immobile tiller particles (spheres, fibers, platelets) on polymer-blend phase separation is investigated computationally using a gene ralization of the Cahn-Hilliard-Cook (CHC) model. Simulation shows that the selective affinity of one of the polymers for the filler surface leads to the development of concentration waves about the filler particles at sin ea rly stage of phase separation in near critical composition blends. These "t arget" patterns are overtaken in late-stage phase separation by a growing " background" spinodal pattern characteristic of blends without filler partic les. The Linearized CHC model is used to estimate the number of composition oscillations emanating from isolated filler particles. In far-off-critical composition blends, an "encapsulation layer" grows at the surface of the f iller rather than a target pattern. The results of these simulations compar e favorably with experiments on filled phase-separating ultrathin blend fil ms in which the filler particles are immobilized on a solid substrate. [S10 63-651X(99)12111-1].