Polymer networks as templates for large-scale defect arrays in liquid crystals*

We utilize crosslinked liquid crystalline polymers to drive the assembly of nematic, smectic and cholesteric liquid crystals (LCs) into large-scale, regular arrays of topological point defects. The polymer network is created by dispersing a mesogenic monomer (RM257) in nematic LC. We utilize the method discovered by Orihara and colleagues [1] to fabricate regular arrays of umbilical defects by applying an electric field to a homeotropic cell containing nematic LC with negative dielectric anisotropy. We modify this method using patterned, partially etched electrodes with different symmetries, which enable the formation of regular arrays of defects over the length-scale of several millimeters. We study the structure of the defect array as a function of the geometry of the patterned electrodes. The polymer network, which is crosslinked while an electric field is applied, can then be emptied and re-filled with nematic, smectic, and cholesteric LCs, to which it imposes its alignment. This strategy allows us to create stable, but tunable optical gratings.
References: [1] Y. Sasaki, V.S.R. Jampani, C. Tanaka, N. Sakurai, S. Sakane, K.V. Le, F. Araoka, H. Orihara, Nat. Commun. 7, 13238 (2016)