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Adsorption and desorption of ions at interface between liquid crystal and alignment layer in liquid crystal displays play a crucial role in residual direct current voltage associated with image sticking. In this article, the dependency of such adsorption and desorption of ions on resistivity of alignment layer and sign of liquid crystal dielectric anisotropy in the fringe-field liquid crystal cell has been investigated. Our studies show that the time constant of ions during adsorption and desorption depends upon resistivity and dielectric constant of liquid crystal and alignment layer, and most strongly influenced by the resistivity of alignment layer such that the one with lower resistivity in two orders shows much faster adsorption and desorption at the interface than that of the one with higher resistivity.

Defects in graphene governs electrical and optical properties. Although grain boundaries in graphene inevitably formed during large area synthesis process, which act as scattering centers for charge carriers to degrade mobility, have been studied extensively, point defects have been rarely investigated mainly due to the absence of facile observation tools. Here, we report polarized optical microscopy to observe defect distributions in monolayer graphene. This was realized by aligning liquid crystal s (LC) on graphene where the defect population was modulated by irradiating ultraviolet (UV) light directly on graphene surface under moisture condition. Aromatic rings in LC molecules are oriented with hexagonal rings in graphene to have preferred orientation, providing a way to identify relative orientations of graphene domains and point defects. Our studies show that point defects generated by prolonged UV irradiation time give rise to irregular LC alignment with disclination lines on the graphene surface and a large-size LC domain associated with graphene single domain eventually disappeared. This indicates that defects associated with oxygen-containing functional groups cause to reduce the strong stacking interaction between graphene and LC molecules. (C) 2015 Optical Society of America

A polymer-stabilized vertical alignment (PS-VA) mode using a new type of photoreactive monomer for polymer stabilization of the liquid crystal (LC) director was developed. Conventional reactive mesogens having a higher molecular weight than those of the host LC tend to aggregate and form large-sized polymer grains when exposed to ultraviolet (UV) light, subsequently deteriorating the quality of the dark state. To address these problems, bis(4-hydroxyphenyl) diacrylates were synthesized with four different linking groups as stabilizing monomers (SMs) which have molecular weights similar to that of the host LC. Their stabilizing characteristics with respect to the molecular size and polarity of SMs were evaluated by examining the electro-optic characteristics of LC cells after UV irradiation. The results showed that the SM containing a small linking group in size between biphenyls with high polarity was favored to achieve excellent polymer stabilization. The SM containing an ether linkage showed excellent electro-optic characteristics with no large-sized polymer grains even in the absence of a photo-initiator. Consequently, we anticipate that SMs, polar and smaller in size, can improve the electro-optic characteristics in PS-VA mode.