59th Annual Report on Research 2014

Surfactant solutions are used in a wide range applications from fracking fluids in the oil and gas industry to heat-transfer fluids in the chemical process industries to various personal care and cleaning products. At sufficiently high concentration, surfactants self-assemble into micelles that can take on a variety of forms including cylindrical, or wormlike. Wormlike micellar surfactant solutions display extremely complex behavior when subjected to flow, and in particular can display dramatic increases in viscosity that are arise due to a flow-induced transition from an isotropic liquid to a nematic-like ``gel'' phase. In many fluids this transition is transient while in others it can be irreversible. The basic molecular mechanisms underlying this transition are understood to some extend but this understanding has not yet been translated into a mathematical model (constitutive equation) that can be used to predicted the stresses and phase behavior of surfactant solutions in the complex flow systems characteristic of many engineering applications. We are using the tools of statistical mechanics, kinetic theory and continuum mechanics to develop continuum-level models of surfactant dynamics that are suitable for integration into fluid-dynamics calculations. Initial work has focused on a stochastic simulation approach to the dynamics of interacting suspended rigid rods; this will be used to motivate and validate the continuum models.