Enhancement of concentration fluctuations in solutions subject to external fields

Abstract : This paper discusses the phenomena of the coupling of concentration fluctuations in complex fluids to external hydrodynamic and electric fields. The use of modified Cahn-Hilliard models to describe this phenomena is presented, along with experimental methods to measure flow-induced structure. It is demonstrated that the application of flow to polymer solutions can enhance concentration fluctuations in the direction perpendicular to the principal axis of strain, and produces butterfly shaped structure factors. Electric fields, on the other hand, distort fluctuations parallel to the applied field, and can induce a real shift of the coexistence curve. In viscoelastic surfactant solutions subject to flow, concentration fluctuations under go a transition from perpendicular flow alignment to parallel flow alignment on time scales associated with the breakage time of wormlike micelles.