Yuriy Garbovskiy

Switching between purification and contamination regimes governed by the ionic purity of nanoparticles dispersed in liquid crystals

This paper reports non-trivial effects of the ionic purity of nanoparticles on the concentration of ions in liquid crystals. Nanoparticles dispersed in liquid crystals can affect the concentration of mobile ions in different ways. 100% pure nanoparticles can only decrease the concentration of ions by means of adsorption/desorption processes. Liquid crystals doped with contaminated nanoparticles exhibit three regimes, namely, the purification, contamination, and no change in the concentration of ions. Switching between these regimes is governed by three dominant factors: the purity of liquid crystals, the purity of nanoparticles, and the ratio of the adsorption rate to the desorption rate.

Electrical conductivity of lyotropic and thermotropic ionic liquid crystals consisting of metal alkanoates

The electrical properties of ionic smectic liquid crystal (ISLCs), specifically, (i) oriented and non‐oriented samples of lyotropic ISLC potassium caproate and (ii) oriented samples of thermotropic ISLC cobalt decanoate, are investigated in detail. The electrical conductivity of lyotropic smectic potassium caproate is higher than that of isotropic electrolytes. A giant anisotropy in the electrical conductivity of oriented samples of thermotropic ISLC cobalt decanoate is observed. The mobility of charge carriers in lyotropic ISLC is measured for the first time. The unusual electrical properties of ISLCs, which are governed by their layered structure, show that they have application potential in optoelectronic devices.

Electrical properties of liquid crystal nano-colloids analysed from perspectives of the ionic purity of nano-dopants

ABSTRACT The concentration of mobile ions in liquid crystals doped with nano-objects is analysed in the framework of the Langmuir isotherms assuming an ionic contamination of nano-dopants. The level of the ionic purity of nano-dopants is described by means of the dimensionless contamination factor. The applicability of the proposed approach is verified by fitting the broad variety of the existing experimental data. A good agreement between theoretical predictions and experimental data indicates the feasibility of the idea to consider nano-dopants partially contaminated. In addition, it provides the way to deduce a set of important parameters (the surface density of the adsorbing sites, the contamination factor and the ratio of the adsorption constant to the desorption constant) directly from electrical measurements. Graphical Abstract

Ion trapping by means of ferroelectric nanoparticles, and the quantification of this process in liquid crystals

Nanoparticles embedded in liquid crystals can trap mobile ions and decrease their concentration. In this paper, we generalize the nanoparticles-based approach and, through the quantitative analysis, identify the ferroelectric micro- and nanomaterials as the most promising “ion traps” that ensure close to 100% liquid crystal purification. We demonstrate that the treatment of liquid crystals with ferroelectric materials leads to a two-order of magnitude decrease in their electrical conductivity. This value exceeds previous data reported for similar systems by a factor of 10. Ferroelectric nanoparticles, when dispersed and stabilized in liquid crystals, act as highly efficient permanent ion traps, solve the problem of uncontrolled ionic contaminations, and eliminate the negative effects caused by ions.

Adsorption/desorption of ions in liquid crystal nanocolloids: the applicability of the Langmuir isotherm, impact of high electric fields and effects of the nanoparticle’s size

ABSTRACT In this paper, the applicability and limitations of the Langmuir formalism applied to describe the ion adsorption/ion desorption in liquid crystal nanocolloids are discussed. The overall electrical neutrality of liquid crystals and nanoparticles is a key factor enabling the validity of the Langmuir isotherms. The approximation of the Langmuir adsorption isotherm is valid as long as the electrical potential of the nanoparticle’s surface is relatively small (), and the applied electric field is not very high (). Within these limits the Langmuir formalism can describe a broad variety of existing experimental data including the dependence of the concentration of mobile ions in liquid crystal nanocolloids on the size of nano-dopants. Graphical Abstract

Impact of contaminated nanoparticles on the non-monotonous change in the concentration of mobile ions in liquid crystals

ABSTRACT The ionic purity of nanoparticles can affect electrical properties of liquid crystals in very unusual ways. While 100% pure nanoparticles can only decrease the concentration of mobile ions in liquid crystals by means of adsorption/desorption processes, nano-dopants contaminated with ions can lead to the increase, decrease and no change in the concentration of ions. Moreover, these changes can exhibit non-monotonous behaviour as a function of the nanoparticle loading. The level of the liquid crystal contamination or purification, achieved by doping them with nanoparticles, is always limited by the physical quantity called the critical concentration of ions. From applied perspectives, results presented in this paper can be used in the selection of nano-materials, the most suitable for the liquid crystal purification. GRAPHICAL ABSTRACT

Optical/ferroelectric characterization of BaTiO3 and PbTiO3 colloidal nanoparticles and their applications in hybrid materials technologies.

In this paper, we will explore how optical and ferroelectric properties of the stressed ferroelectric nanoparticles prepared through ball milling set a limit on the performance of optical and electro-optical devices based on such materials. It was found that suspensions of BaTiO3 nanoparticles exhibit a blue shift in the optical band gap with a decrease in particle size. The optical band gap of PbTiO3 nanoparticles is not affected by the milling time. Polarization switching is composed of slow and fast components. A slow component is threshold-less and is caused by the particle reorientation while a fast component has a threshold, and its rise time is inversely proportional to the electric field. The absorption edge of these suspensions accounts for the applications in the near UV range, while kinetics of the polarization switching governs the speed of electro-optical devices.

Nanoparticle enabled thermal control of ions in liquid crystals

ABSTRACT Typically, ionic species in thermotropic liquid crystals are nearly fully ionised. Therefore, the concentration of mobile ions practically does not depend on the temperature. Interestingly, the same liquid crystals doped with nanoparticles exhibit totally different behaviour. The concentration of mobile ions become temperature dependent. This paper reports the effects of the temperature on the concentration of ions in liquid crystal nanocolloids. Liquid crystals doped with both 100% pure and contaminated nanoparticles are considered. Regardless the ionic purity of nanodopants, the concentration of mobile ions in liquid crystal nanocolloids increases towards the saturation as their temperature goes up. The magnitude of this saturation level equals the initial concentration of ions in liquid crystals doped with 100% pure nanoparticles. The temperature induced release of ions by contaminated nanoparticles in liquid crystals increases the above-mentioned saturation level. While the dispersion of 100% pure nanoparticles in liquid crystals leads to the temperature-dependent purification only, the use of contaminated nanoparticles results in the temperature-driven switching between the purification and contamination regimes enabling thermal control of ions. GRAPHICAL ABSTRACT

Ion capturing/ion releasing films and nanoparticles in liquid crystal devices

Nanoparticles dispersed in liquid crystals can change the concentration of mobile ions through the adsorption/desorption process. In the majority of the reported cases, the effects of nanoparticles on the electrical properties of liquid crystals are analysed, neglecting the interactions of ions with substrates. In this paper, the combined effect of nanoparticles and substrates on the concentration of ions in liquid crystals is discussed. Depending on the ionic purity of substrates and nanoparticles, the ion capturing/ion releasing regimes can be achieved. In addition, the concentration of mobile ions in liquid crystal nanocolloids also depends on the cell thickness.

Nonlinear optical properties of composites based on conductive metal-alkanoate liquid crystals

The dynamic holography in new composite materials based on a novel class of metal-alkanoate ionic liquid crystals (ILCs) is studied experimentally and theoretically. The composites are formed as a dielectric dye film covered by lyotropic metal-alkanoate ILC and ionic smectic glasses with doped dye molecules. The dynamic gratings are created by nanosecond pulses of double frequency Nd:YAP laser, the recording demonstrates fast erasure time of residual thermal gratings. The nonlinear optical properties are determined by the resonance nonlinearity in photosensitive centres of ILC. Note, that permanent relief gratings will be formed on a dielectric dye film only as well as in composite cells either with nematic LC or with polymers under action of pulsed laser radiation. Lyotropic ILC layer applied over the dye film provides the dynamic regime of grating recording in composite cells. We found a secondary thermal grating is much smaller, the conductive ILC matrix provides effective heat dissipation and erasure of this thermal grating. A theory of Raman-Nath self-diffraction holography on thin films followed from the wave equation and the nonlinear mechanism of absorption saturation is developed to explain experimental results.