The dynamics of colloids in a narrow channel driven by a non-uniform force

Using Brownian dynamics simulations, we investigate the dynamics of colloids confined in two-dimensional narrow channels driven by a non-uniform force F(y). We considered linear-gradient, parabolic and delta-like driving-force profiles. This driving force induces melting of the colloidal solid (i.e., shear-induced melting), and the colloidal motion experiences a transition from elastic to plastic regime with increasing F. For intermediate F (i.e., in the transition region) the response of the system, i.e., the distribution of the velocities of the colloidal chains, in general does not coincide with the profile of the driving force F(y), and depends on the magnitude of F, the width of the channel and the density of colloids. For example, we show that the onset of plasticity is first observed near the boundaries while the motion in the central region is elastic. This is explained by: (i) (in)commensurability between the chains due to the larger density of colloids near the boundaries, and (ii) the gradient in F. Our study provides a deeper understanding of the dynamics of colloids in channels and could be accessed in experiments on colloids (or in dusty plasma) with, e.g., asymmetric channels or in the presence of a gradient potential field.