Electrically-driven Light-induced Control of Liquid Crystal in a Cell with Fullerene-containing Layer

摘要

We report on the first observation of surface-mediated reorientation effect in LC with fullerene-containing aligning polymer. We found a strong light-induced change of the Friedericksz transition voltage in a de-field. The Friedericksz transition was measured in a LC cell containing reference and command surfaces. The reference surface, covered with the photoaligning material fluoro-polyvinyl-cinnamate (PVCN-F), was irradiated with polarized UV-light providing strong unidirectional planar alignment. The command surface was covered with a mixture of PVCN-F and fullerene in a 2:1 ratio. This layer was also irradiated with UV-light to obtain unidirectional planar alignment. The 90°-twist cell (thickness ≈30μm) was filled with LC 5CB in the nematic phase. We found a strong increase of the Friedericksz transition voltage as the intensity of the incident beam from He-Ne laser was increased. The effect was reversible and depended on the sign of electric field applied to the cell. We suggest that the increase of Friedericksz transition voltage arises from charge injection into the LC bulk from the fullerene-containing alignment layer. An enrichment of the ion concentration near the surface causes a redistribution of the electric field in the cell, localizing it more strongly near the surface, and, thus, leading to an increase of the voltage necessary to reorient the director.