Dynamics from an equilibrium lattice model of a microemulsion

A 3D lattice model of three-component microemulsion employed previously to describe the equilibrium phase behavior has been extended to investigate the nonequilibrium dynamics of such system. The model is based on Dynamical Monte Carlo simulations which apply a coarse-grained velocity field onto a conventional Monte Carlo lattice, so as to represent realistically interactions between particles, and which permits the observation of time-dependent behavior. The results for viscosity are obtained by applying the velocity gradient onto the system. The simulations are performed over a range of shear rates and temperatures. Compared to the oil-rich (water-rich) phase, the microemulsion phase shows a typical (non-Newtonian) behavior and considerably lower viscosity at a given temperature. Both phases exhibit the characteristic viscosity decrease with an increase in temperature. The velocity auto-correlation function of a microemulsion phase is found to follow a Kohlrausch-Wiliams-Watts (KWW) stretched-exponential law, rather than a simple exponential decay. The stretched exponent is related to the normal, inhibited and enhanced diffusion behaviors of the system