Flow birefringence at the sol-gel transition

Abstract

The information provided by a flow birefringence experiment at the sol-gel transition in the sol phase is discussed There are two competing effects : cluster rotations, and cluster elastic deformation. In a steady state, rotational effects turn out to be dominant. For small velocity gradients S we predict an extinction angle x such that π/4 - x diverges with an exponent roughly equal to 3.4 i.e. a very strong effect In the vicinity of the transition, the birefringence Δn has the same divergence as the macroscopic viscosity.