Structures and alignment of anisotropic liquid crystal particles in a liquid crystal cell

Abstract

Anisotropic porous liquid crystal (LC) particles with ∼60 μm diameters were prepared using microfluidics and directional UV photopolymerization of 1,4-bis[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene/4-cyano-4′-pentylbiphenyl (RM257/5CB) mixtures at room temperature in the presence of a magnetic field. RM257 and 5CB in the RM257/5CB mixtures were reactive mesogen and orientation-inducible LC porogen, respectively. The RM257/5CB droplets coated with sodium dodecyl sulfate (SDS) (RM257/5CB_SDS) and poly(vinyl alcohol) (PVA) (RM257/5CB_PVA) showed radial and bipolar configurations, respectively, while UV photopolymerization locked their orientations in the solid particles. During UV photopolymerization, a magnetic field was applied to align the anisotropic bipolar RM257/5CB_PVA droplets. When the direction of the UV beam was parallel to the axis of the two defect poles of the bipolar RM257/5CB_PVA droplets, highly anisotropic LC particles were produced. In the absence of a magnetic field during UV photopolymerization, the resultant LC particles, after the removal of 5CB, had helical structures owing to the replacement of energetically expensive splay deformation with twisted ones at the defect poles. The detailed internal orientation in the anisotropic LC particles was studied using more than 240 two-dimensional micro-beam X-ray diffraction patterns per particle, which provided the detailed orientation director field in the particle. The porous structure produced by the LC porogen induced the infiltration of 5CB into the LC particles in an LC cell, which caused the rotation of the anisotropic LC particles along the rubbing direction in the polyimide-coated LC cell. The combination of the porous structure and alignment of the LC chains in the anisotropic LC particles exhibited this unique rotating ability in the LC cell.