Kurochkin O. Influence of ferroelectric particles Sn2P2S6 on the properties of nematic and cholesteric liquid crystals.

This thesis deals with investigation of phase transitions, orientational, optical and electro-optical properties of colloids of ferroelectric nanoparticles Sn2P2S6. It was shown experimentally that characteristics of the ferroelectric colloids differ from the same characteristics of pure liquid crystals (LCs). The particles in tiny concentration may change properties of the LC matrix. It was shown that the ferroelectric nanoparticles Sn2P2S6 shift the clearing temperature, extend the two-phase coexistent region, and change the average order parameter of the single-component nematic liquid crystal 5CB. These effects are common for molecular additives. The order parameter of the colloids showed the universal temperature behavior, which is a characteristic of the LCs with molecular additives. It was found what mechanism of the influence of ferroelectric particles on liquid crystal host is different for single- and multi-component LCs. The order parameter and clearing temperature decreases slightly for colloids of ferroelectric particles Sn2P2S6 in LC ZLI 4801 matrix, but dielectric anisotropy and birefringence of the colloids on the base of multi-component LC are larger than those of pure LC. The influence of the ferroelectric nanoparticles on the induced cholesteric LCs results in a strong change of the mesogenic, optical and electro-optical properties of the mixtures. It was shown that the drop of the driving voltage and changes of the spectral characteristics of cholesteric LC was caused by a strong increase of the effective dielectric anisotropy and birefringence of the nematic matrix, which was the basic component of the cholesteric compound.