Condensed Matter Theory

Abstract:

Active liquid crystals or active gels are soft materials which can be physically realised, e.g. by preparing a solution of cytoskeletal filaments interacting with molecular motors. We study the hydrodynamics of an active liquid crystal in a slab-like geometry with various boundary conditions, by solving numerically its equations of motion via lattice Boltzmann simulations. In all cases we find that active liquid crystals can sustain spontaneous flow in steady state contrarily to their passive counterparts, and in agreement with recent theoretical predictions. We further find that conflicting anchoring conditions at the boundaries lead to spontaneous flow for any non-zero value of the 'activity' parameter, while with unfrustrated anchoring at all boundaries spontaneous flow only occurs when the activity exceeds a critical threshold. We finally discuss the dynamic pathway leading to steady state in a few selected cases. (c) 2007 Elsevier B.V. All fights reserved.

Abstract:

A conformation space kinetic model is constructed to drive the deformation cycle of a three-sphere swimmer to achieve propulsion at low Reynolds number. We analyze the effect of an external load on the performance of this kinetic swimmer and show that it depends sensitively on where the force is exerted, so that there is no general force-velocity relation. We discuss how the conformational cycle of such swimmers should be designed to increase their performance in resisting forces applied at specific points.