Reduced ionic effects and enhanced spontaneous polarization in a ferroelectric liquid crystal device employing a two-dimensional hexagonal boron nitride planar-alignment agent

The presence of excess free-ion impurities in ferroelectric liquid crystals (FLCs) results in several issues in electro-optical liquid-crystal displays (LCDs), such as slow electro-optical responses and image-sticking effects. This study experimentally demonstrated that two-dimensional (2D) hexagonal boron nitride (h-BN) nanosheets can function as both planar alignment and ion-capturing agents in an electro-optic FLC device. The 2D h-BN nanosheet was used as a planar alignment agent on one side of an LC cell, while a standard planar-aligning polyimide (PI) layer was used on the other side of the cell. The FLC exhibited uniform planar alignment in this h-BN-PI cell configuration. The results showed that free-ion impurities in the FLC were significantly suppressed in the h-BN-PI cell compared to a standard PI-PI LC cell. This reduction in free-ion density in the h-BN-PI cell was attributed to the ion-capturing capability of the 2D h-BN nanosheets. Consequently, the reduction of ionic impurities led to enhanced effective spontaneous polarization and accelerated electro-optic response of the FLC in the h-BN-based cell.