  We study the phenomenon of migration of the small molecular weight component
of a binary polymer mixture to the free surface using mean field and
self-consistent field theories. By proposing a free energy functional that
incorporates polymer-matrix elasticity explicitly, we compute the migrant
volume fraction and show that it decreases significantly as the sample rigidity
is increased. Estimated values of the bulk modulus suggest that the effect
should be observable experimentally for rubber-like materials. This provides a
simple way of controlling surface migration in polymer mixtures and can play an
important role in industrial formulations, where surface migration often leads
to decreased product functionality.

Soft Condensed Matter;Materials Science;Statistical Mechanics