Manipulating shear-induced non-equilibrium transitions in colloidal films by feedback control

Abstract

Using Brownian Dynamics (BD) simulations we investigate non-equilibrium transitions of sheared colloidal films under controlled shear stress σ_xz. In our approach the shear rate is a dynamical variable, which relaxes on a time scale τ_c such that the instantaneous, configuration-dependent stress σ_xz(t) approaches a pre-imposed value. Investigating the dynamics under this “feedback-control” scheme we find unique behavior in regions where the flow curve σ_xz() of the uncontrolled system is monotonic. However, in non-monotonic regions our method allows to select between dynamical states characterized by different in-plane structure and viscosities. Indeed, the final state strongly depends on τ_c relative to an intrinsic relaxation time of the uncontrolled system. The critical values of τ_c are estimated on the basis of a simple model.