Control of periodic defect arrays of 8CB (4′-n-octyl-4-cyano-biphenyl) liquid crystals by multi-directional rubbing

In this study, we introduce a simple multi-directional rubbing method to generate various periodic patterns of toric focal conic domains (TFCDs), a typical smectic (Sm) LC defect by using the commonly used Sm LC materials, 4'-n-octyl-4-cyano-biphenyl (8CB). We have successfully obtained a variety of spatially arranged TFCD arrays such as parallelogrammic, hexagonal and square arrays by changing the rubbing angle (Omega) between two different rubbing directions. Our experimental results demonstrate that frustration and distortion of nematic LC molecules at the intersections act as effective seeds to help positioning of TFCDs. Furthermore, the existence of nematic-Smectic A (SmA) phase transition is quite important in controlling the arrangement of TFCDs as the alignment of the nematic director strongly influences the arrangement of TFCDs formed in the SmA phase.