Manipulating shear-induced non-equilibrium transitions by feedback control

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