Glassy states and microphase separation in cross-linked homopolymer blends

¹ Institut für Theoretische Physik, Georg-August-Universität Göttingen Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
² Department of Physics, University of Illinois at Urbana-Champaign 1110 West Green Street, Urbana, IL 61801-3080, USA

Received: 4 November 2004
Accepted: 18 April 2005

Abstract

The physical properties of blends of distinct homopolymers, cross-linked beyond the gelation point, are addressed via a Landau approach involving a pair of coupled order-parameter fields: one describing vulcanisation, the other describing local phase separation. Thermal concentration fluctuations, present at the time of cross-linking, are frozen in by cross-linking, and the structure of the resulting glassy fluctuations is analysed at the Gaussian level in various regimes, determined by the relative values of certain physical length scales. The enhancement, due to gelation, of the stability of the blend with respect to demixing is also analysed. Beyond the corresponding stability limit, gelation prevents complete demixing, replacing it by microphase separation, which occurs up to a length scale set by the rigidity of the network, as a simple variational scheme reveals.