A computational study of surface-directed phase separation in polymer blends under temperature gradient

Abstract

To apprehend the real industrial behavior of polymeric materials phase separation phenomenon, the nonlinear Cahn-Hilliard theory incorporating the Flory-Huggins-de Gennes free energy theory was used to study the non-uniform thermal-induced phase separation phenomenon in a symmetric binary polymer blend in which surface(s) with short- and long-range attraction to one polymer component compete with temperature gradient effects. The numerical results indicate that an increase of diffusion coefficient value will increase the rate of phase separation in the bulk but will decrease the growth rate of the wetting layer on the surface regardless of the surface potential strength. Also, the morphology transition from complete to partial wetting of the surface with short range surface attraction is successfully demonstrated. However, no partial wetting is observed for the surface with long-range potential. For shallow quenches, first, a growth rate of t 0.5 is observed in the early stage of spinodal decomposition phase separation at the surface and then a decline in the growth rate to t 0.13 in the intermediate stage occurred. For short- and long-range surface potential, the growth rate value of t 0.33 obtained in the bulk. The morphology results of temperature gradient effect on surface directed spinodal decomposition in short-range, long- range and multiple-surface attraction cases have been presented for the first time. It is realized that regardless of surface potential magnitude, surface enrichment is increased by higher temperature gradient (deep quenches on the side with no surface attraction). The studied models would provide more in depth understanding of polymer blendiprocesses.