Buchnev O. Suspension of ferroelectric nanoparticles Sn2P2S6 and BaTiO3 in nematic liquid crystals

The thesis is devoted to investigation of general mesogenic liquid crystal (LC) properties of new type of liquid crystal materials - low concentrated suspensions of ferroelectric particles Sn2P2S6 and BaTiO3 in nematic liquid crystals. It was found that the adding of ferroelectric particles to a liquid crystal host at small concentration resulted in essential increasing of dielectric anisotropy, birefringence and temperature of "nematic-isotropic liquid" phase transition. Also this led to decreasing of the voltage of electro optic thresholds and appearance of sensitivity LC matrix to sign of the applied field that is unusual for nematic LC. The model of the effect of the ferroelectric particles on the main properties of the nematic liquid crystal was proposed. The origin of the effect was suggested to be due to strong electric field produced by the ferroelectric particles having strong permanent dipole moments that leads to the increasing of the average order parameter. The increase of the average order parameter results in increase of all basic mesogenic characteristics of nematics which are determined by the order parameter, namely dielectric anisotropy, birefringence and temperature of the transition to isotropic phase. Ferroelectric LC nanosuspensions can be very perspective for information displays and optical processing. It was demonstrated that application ferroelectric LC nanosuspensions resulted in essential decrease of the driving voltage of the nematic LC cells operating in twist-mode and decrease of the driving voltage of the cholesteric bistable LC cells. It was also observed that adding of ferroelectric particles to the nematic LC led to strong increase of a light-beam coupling in a LC cell during recording of the photorefractive gratings. The adding of the ferroelectric particles to liquid crystal matrix is effective method of control and modification of liquid crystal properties by not-chemical way.