Temperature Gradients Induced Phase Separation in a Miscible Polymer Solution.

Jiro Kumaki,1 Takeji Hashimoto,1,2 and Steve Granick3 1Hashimoto Polymer Phasing Project, ERATO, JRDC, Keihanna Plaza, Seika, Kyoto 619-02, Japan 2Division of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-01, Japan 3Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801 (Received 27 February 1996) Phase separation occurred up to 20 ±C above the coexistence temperature in a polymer solution (polystyrene-polybutadiene-dioctylphthalate) to which small temperature gradients (ø2 ±C) were applied. Before convection began, spinodal-like patterns with characteristic spacing that grew in proportion to time elapsed persisted for times up to hours. The cause appears to be thermally driven concentration gradients normal to the surface, large enough to induce phase separation parallel to the surface, although temperatures throughout the mixture exceeded the thermodynamic coexistence temperature. [S0031-9007(96)01078-2]