Reconfigurable spatially-periodic umbilical defects in nematic liquid crystals enabled by self-organization

Abstract

Abstract Spontaneous formation of ordered structures is observed in many physical systems. Soft materials such as colloids, polymers, and liquid crystals (LCs) are stimuli-responsive and often form various functional self-organized structures that are interesting not only fundamentally but also regarding applications. Nematic LCs (NLCs) consisting of elongated molecules are characterized by anisotropic molecular orientations that are strongly affected by external fields. In particular, the combination of an applied electric field and surface boundary conditions is commonly used for controlling stable configurations and plays a fundamental role in LC devices. Currently, the standard approach to fabricating complex molecular orientations is to use tailored surfaces that mostly rely on top-down lithographic techniques, with relatively few examples of bottom-up systems that produce patterned structures. Moreover, previously known systems such as electroconvection are quite dynamic and not sufficiently controllable, even though they exhibit a variety of patterns. Therefore, exploring the physical mechanism for the formation of a spontaneous pattern could be important in exploiting the further functional properties of NLCs. Here, we briefly review a unique type of self-organization in NLCs induced by an electric field, where the crucial effects of the polymer layer between the NLC and the electrodes lead to the formation of a two-dimensional periodic structure in the sample cell instead of the standard reorientation process. As well as experimental demonstration of the phenomenon, a descriptive theoretical framework is discussed, as are perspectives for optical applications.