Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 19: SYMPOSIUM Driven Soft Matter IV

CPP 19.2: Talk

Wednesday, February 27, 2008, 14:15–14:30, C 130

Driven polymer blends: criticality and structure formation in inhomogeneous temperature fields — •Werner Köhler, Albert Voit, and Alexei Krekhov — Physikalisches Institut, Universität Bayreuth

Even moderately inhomogeneous temperature fields, as generated by localized laser heating, couple to the order parameter (the composition) and can drive polymer blends far out of equilibrium. Close to the critical point this Soret effect can be four to five orders of magnitude stronger than in conventional liquid mixtures. Global equilibrium phase diagrams loose their meaning, and even UCST-mixtures can be quenched into phase separation by local heating. Close to the critical point we observe critical scaling, and almost arbitrary composition patterns can be written into a PDMS/PEMS blend using a galvano laser scanner. Below the spinodal the prescribed patterns compete with the intrinsic length scale of the correlation length, and surface tension effects become increasingly important. The theoretical modelling of the structure formation is based on a modified Cahn-Hilliard-equation, and 2D-models are able to reproduce the essential spatio-temporal features. While the susceptibility (Soret coefficient) diverges at the critical point of the liquid-liquid phase transition, it is completely insensitive to a glass transition due to a cancellation of local friction being effective on the molecular length scale of a few monomers.

[1] A. Voit, A. Krekhov, W. Enge, L. Kramer, W. Köhler, PRL 94 (2005) 214501; [2] A. Voit, A. Krekhov, W. Köhler, Macromolecules 40 (2007) 9; [3] A. Voit, A. Krekhov, W. Köhler, PRE 70 (2007) 011808