Rheology and Structure of Quenched Binary Mixtures Under Oscillatory Shear

Abstract

We applied the D2Q9 BGK lattice Boltzmann method to study the rheology and structure of the phase separating binary fluids under oscillatory shear in the diffusive regime. The method is suitable for simulating systems whose dynamics is described by the Navier-Stokes equation and convection-diffusion equation. The shear oscillation induces different rheological patterns from those under steady shear. With the increasing of the frequency of the shear the system shows more isotropic behavior, while with the decreasing of the frequency we find more configurations similar to those under steady shear. By decreasing the frequency of the shear, the period of the applied flow becomes the same order of the relaxation time of the shear velocity profile, which is inversely proportional to the viscosity, and more anisotropic effects become observable. The structure factor and the velocity profile contribute to the understanding of the configurations and the kinetic process. Oscillatory shear induces nonlinear pattern of the horizontal velocity profile. Therefore, configurations are found where lamellar order close to the wall coexists with isotropic domains in the middle of the system. For very slow frequencies, the morphology of the domains is characterized by lamellar order everywhere that resembles what happens in the case of steady shear.