Diffusion in polyelectrolyte solutions

Abstract

Molecular migration in nonhomogeneous flows of a polyelectrolyte solution is considered. The solution is modelled as a binary mixture whose electrically-charged constituents are regarded as compressible fluids. Upon deriving a set of thermodynamic restrictions for the mixture, non-equilibrium quantities are examined in detail. As a result, two schemes are elaborated for the description of cross streamline migration, induced by the second gradient of the velocity, where also occur coupling effects. In the first scheme the migration effect is described through a stress term which involves a coupling with the conformation of the macromolecule; in the second scheme it is described through a term in the diffusion velocity where coupling occurs with the velocity gradient. In both cases the thermodynamic approach leads to a systematic framework with a minimal number of constitutive coefficients, which is an essential aspect for any comparison with experimental data.