HYDRODYNAMIC EFFECTS IN THE PHASE-SEPARATION OF BINARY POLYMER MIXTURES

The phenomenon of phase separation by spinodal decomposition was studi ed for polymer blends made by compositional quenching. The modified Ca hn-Hilliard theory of phase separation was extended to include hydrody namics, with a volumetric body force, due to concentration gradients, that induced convective flows. This force influenced the morphology an d the growth rate of the average domain size. Unlike the conventional treatment of flows driven by surface tension, the velocity and pressur e fields were treated as continuous functions of spatial position. Num erical solutions for the phase separation in a binary mixture were obt ained for a three-dimensional system with periodic boundary conditions . For near critical quenches with similar volume fractions, for the tw o components, cocontinuity was destroyed by the hydrodynamics, giving discrete domains. The breakup in interconnectivity is believed to be a universal phenomenon. The domain growth rate followed a power law, r --> tau(n). The growth exponent depended on the dimensionless viscosit y group, zeta = (R(g)T/nu(s)) (kappam/muD(AB)) and ranged from n = 0.3 2 +/- 0.006 for zeta = 0 (no hydrodynamic effects) to n approximately 1 for zeta = 1. For off-critical quenches in which a dispersed phase w ould be formed by diffusion alone, the scaling exponent showed little enhancement. The simulations accurately predicted the particle size fo rmed in the early stages of spinodal decomposition.