Yurii Reznikov

Ferroelectric nematic suspension

We report on the development of a dilute suspension of ferroelectric particles in a nematic liquid-crystal (LC) host. We found that the submicron particles do not disturb the LC alignment and the suspension macroscopically appears similar to a pure LC with no readily apparent evidence of dissolved particles. The suspension possesses enhanced dielectric anisotropy, and is sensitive to the sign of an applied electric field.

Fast birefringent mode stressed liquid crystal

We report a stressed liquid crystal (SLC) that produce a large shift in phase retardation at submillisecond speeds. The SLC consists of uniformly aligned micro-domains of a liquid crystal dispersed in a polymer structure. Mechanical stress produces uniform alignment, essentially eliminates light scattering, and substantially improves the electro-optic performance. A 22-μm-thick SLC film switches more than 2μm of phase retardation in less than 1ms. The system has a linear voltage response with essentially no hysteresis.

HIGH RESOLUTION POLARIZATION GRATINGS IN LIQUID CRYSTALS

Efficient recording of polarization gratings in dye-doped liquid crystals is reported. By exploiting the effect of light-induced anchoring of the molecular director, it has been possible to write stable holographic gratings with a diffraction efficiency of 8% at a resolution of 1000 lines/mm. The required surface energy density of 0.3 J/cm2 sets these materials among the most sensitive for optical storage.

Ferroelectric particles-liquid crystal dispersions

Long-range forces between ultra-fine particles imbedded in liquid crystal (LC) result in intriguing colloids. Embedded inorganic particles in LC contribute to the properties of the LC matrix. Large (>>mkm) colloidal particles form defects in LC matrices due to strong director deformations and ensembles of these particles and defects can form complex structures. Small particles at its high concentration (> 2-3% by weight) create almost a rigid LC suspension. We show that at low concentrations LC submicron colloids appear similar to a pure LC with no readily apparent evidence of dissolved particles, but possess unique properties. The diluted suspensions are stable, because the small concentration of submicron particles does not significantly perturb the director field in the LC, and interaction between the particles is weak. At the same time, the submicron particles share their intrinsic properties with the LC matrix due to the anchoring with the LC. We report on the development and unique properties of the diluted suspensions of ferroelectric submicron particles. Our results show that doping a nematic LC matrix with ferroelectric submicron particles results in a suspension, which possesses an enhanced dielectric anisotropy and reveals ferroelectric and paraelectric properties inherent to the submicron particles. In particular, we observed essential decrease of the driving voltage of the quadratic dielectric response and non-usual linear dipole response of the suspensions on the application of ac-field. We present a theoretical model of dielectric properties of ferroelectric suspensions.

Temperature induced anchoring transition in nematic liquid crystal cell

We found a thermally-induced threshold reorientation of the nematic liquid crystal from homeotropical alignment to planar one. The fenomenon was observed in a symmetric cell with inner surfaces covered with fluoro polyvinyl-cinnamate. This threshold reorientation is an anchoring transition of the second order. We suggest that a competition of aligning abilities of flexible polymer fragments and main polymer chains is the basic reason for this phenomenon.

Diluted ferroelectric suspension of Sn2P2S6 nanoparticles in nematic liquid crystal

Long-range forces between ultra-fine particles imbedded in liquid crystal (LC) matrices result in intriguing colloids. Embedded inorganic particles in LC contribute to the properties of the LC matrix. For example, doping of a LC with ferromagnetic particles resulted in a strong enhancement of magnetic properties of the LC. Large (>>µm) colloidal particles form defects in LC matrices due to strong director deformations and ensembles of these particles and defects can form complex structures. Small (<2-3% by weight) create almost a rigid LC suspension. Here we show that at low concentrations LC nanocolloids appear similar to a pure LC with no readily apparent evidence of dissolved particles, but possess unique properties. The diluted suspensions are stable, because the small concentration of nanoparticles does not significantly perturb the director field in the LC, and interaction between the particles is weak. At the same time, the nanoparticles share their intrinsic properties with the LC matrix due to the anchoring with the LC. In particular, doping a nematic LC matrix with ferroelectric nanoparticles results in a suspension, which possesses an enhanced dielectric anisotropy and reveals ferroelectric and paraelectric properties inherent to the nanoparticles.

Magnetically controlled anchoring of nematic liquid crystal

We consider the effect of magnetically controlled anchoring of ferro-nematic suspensions. Together with co-authors we recently found that application of weak magnetic field to a cell filled with the ferro-suspension induced an axis of easy orientation of the director of liquid crystal on a polymer surface (Mol. Cryst. Liq. Cryst., 375, 81, (2002). Here we present a simple theoretical model of the effect that assumed coupling between liquid crystal and the applied magnetic field. This coupling is assumed to be a combination of the interaction between magnetic field with ferro-particles magnetic momentum on the one hand and LC director anchoring with these particles on the other hand.