Externally Controllable Nematic Flow Induced by Active Surface Anchorings

Usually, active matters exhibit some sort of nematic order which constantly is distorted due to internal activity of the system. But can this also happen in reverse? Can nematic order distortions cause stable activity in intrinsically passive systems? Well, there is a phenomenon called backflow effect. This means that elastic distortions can cause flux in nematic liquid crystals (NLC). However, to achieve a net flux, the distortions must be induced in a non-reciprocal manner. One of the most effective ways to induce the elastic distortions into the bulk of the NLC is to change the boundary conditions in time and space, which we call active surface anchoring. Our simulations show that if the surface anchoring on the surface non- reciprocally changes in time, e.g., like a wave, there will be a back-and-forth flow with a nonzero time average, as in a heartbeat. In experiments, this can be achieved by grafting photosensitive elastomers onto the surface. Such elastomers reversibly change their folding by UV and visible light, leading the surface anchoring switch between planar and homeotropic.