Control of liquid crystal order by surface electric fields and microstructuring

Microstructured cells with optical feedback were filled with nematic liquid crystals. The cells were assembled by combining planar ITO substrates and gold-coated hemispherical micro-mirrors. Optical reflection images showed a remarkable change of symmetry in the back-reflected, polarised light when an external voltage was applied. Theoretical modelling of the alignment of the liquid crystals, confined in microstructured cells, was carried out in parallel with the experimental work. The motion of defects under the effect of the applied cross-sections of simulated molecular director inside the microcavity for 0 V (top) and 10 V (bottom) electric field was predicted and this effect can be responsible for the change of symmetry of the back-reflected light. Surface charging effects are also studied, the results indicate that the reorientation grating originates from the build-up and discharge of surface charge screening layers, spatially modulated due to the photoconductivity of doped poly(N-vinyl carbazole) (PVK). The formation and subsequent discharge of surface charge screening layers can, in fact, be the main force influencing the reorientation of liquid crystal molecules