In situ laser-imprinted surface realignment of a nematic liquid crystal

We present a new method for the in-plane realignment of nematic liquid crystals in already fully assembled cells with uni-directionally rubbed polyimide as an aligning layer. We use nematic liquid crystals (NLCs) with a relatively high nematic-isotropic transition temperature and we focus the IR laser beam of the laser tweezers selectively onto one or the other of the inner interfaces. The heat generated by the IR absorption locally melts the liquid crystal and creates an isotropic island with well-defined molecular anchoring at the nematic-isotropic interface. By scanning the laser beam along a pre-defined line, the moving isotropic-nematic interface leaves behind a well oriented LC domain, with LC molecules aligned at 45° to the rubbing direction. If we in addition move the sample with respect to this scanning line, we would be able to selectively realign micro-domains of the liquid crystal with respect to the original alignment induced by the PI rubbing. The realignment can be performed independently on each LC-glass interface, thereby producing predefined domains with customized and controllable alignment within an otherwise uniformly aligned cell.