Tatyana A. Mirnaya

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.

Monodispersity and ordering of semiconductor quantum dots synthesised in ionic liquid crystalline phase of cadmium alkanoates

Structural and optical properties of cadmium alkanoates nanocomposites with cadmium sulfide (CdS) quantum dots (QDs) have been studied by using various techniques: small angle X-ray scattering, transmission electron microscopy, optical absorption spectroscopy and photoluminescence. QDs are chemically synthesised in thermotropic ionic liquid crystalline (ILC) phase of cadmium alkanoates that have smectic-type ordering and are used as nanoreactors. Anisotropic glassy nanocomposites are obtained by rapid cooling the thermotropic ILC nanocomposites to the room temperature. For synthesis of CdS QDs are used cadmium capronate matrix or cadmium octanoate matrix and their binary mixture. Our results show that in the new cadmium alkanoates matrices, the CdS QDs have a small dispersion of their sizes, their shape is nearly spherical, they are stable over time and they are ordered in a layered smectic A matrix. QDs in cadmium octanoate and in cadmium capronate matrices have the dominant characteristic sizes of 2.7 and 2.8 nm, respectively. In the binary mixture, the QDs have two dominant characteristic sizes of 2.7 and 3.6 nm. The glassy nanocomposites show spectra both of absorption and of photoluminescence in near-ultraviolet and blue visible spectral range.

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.

Structural characteristics of different types of nanoparticles synthesised in mesomorphic metal alkanoates

ABSTRACT The class of thermotropic ionic liquid crystals (LCs) of the metal alkanoates possesses a number of unique properties, such as intrinsic ionic conductivity, high dissolving ability and ability to form time-stable mesomorphic glasses. These ionic LCs can be used as nanoreactors for the synthesis and stabilisation of different types of nanoparticles (NPs). Thus, some semiconductors, metals and core/shell NPs were chemically synthesised in the thermotropic ionic liquid crystalline phase (smectic A) of the cadmium octanoate (CdC8) and of the cobalt octanoate (CoC8). By applying the scanning electron microscopy, the cadmium and cobalt octanoate composites containing CdS, Au, Ag and core/shell Au/CdS NPs have been studied. NPs’ sizes and dispersion distribution of the NPs’ size in the nanocomposites have been obtained. GRAPHICAL ABSTRACT

Mesomorphic glass nanocomposites made of metal alkanoates and nanoparticles as emerging nonlinear-optical materials

Mesomorphic metal alkanoates is very promising yet overlooked class of nonlinear-optical materials. Metal alkanoates can exhibit a broad variety of condensed states of matter including solid crystals, plastic crystals, lyotropic and thermotropic ionic liquid crystals, liquids, mesomorphic glasses, and Langmuir–Blodgett films. Glass-forming properties of metal alkanoates combined with their use as nano-reactors and anisotropic host open up simple and efficient way to design various photonic nanomaterials. Despite very interesting physics, the experimental data on optical and nonlinearoptical properties of such materials are scarce. The goal of the present paper is to fill the gap by discussing recent advances in the field of photonic materials made of metal alkanoates, organic dyes, and nanoparticles. Optical and nonlinear-optical properties of the following materials are reviewed: (i) mesomorphic glass doped with organic dyes; (ii) smectic glass composed of cobalt alkanoates; (iii) semiconductor nanoparticles embedded in a glassy host; (iv) metal nanoparticles - glass (the cobalt octanoate) nanocomposites.

Photorefractive processes in dye-doped ionic lyotropic liquid crystals

Two-wave mixing holography experiments with Raman-Nath diffraction in ionic lyotropic liquid crystals (ILLC) pure and doped by polymethine dyes is observed for the first time. The laser generation in ILLC films doped by polymethine dyes is demonstrated. Pure and doped ILLC is considered as new perspective photorefractive material for applications in signal and information processing.

Nonlinear Optical Properties of New Nanocomposites: Metal Alkanoate Glasses with Semiconductor Quantum Dots

Nonlinear optical properties of cadmium alkanoate composites with CdSe nanoparticles are investigated. The standard Z-scan technique with CW laser (λ = 405 nm) and CW laser with chopper was used for this purpose. The nonlinear characteristics of nanocomposites contained CdSe quantum dots (QDs) of different sized were measured.

Spectral and electric properties of cobalt (II) ions in liquid crystalline metal decanoate systems

Metal alkanoates (systems based on lead decanoate with Co2+) under their melting were investigated. Electronic absorption spectra of Co2+ in the isotropic melt, ionic smectic mesophase and crystal phase were studied as a function of temperature. Dielectric properties and conductivity of ILC also were observed.

Electro-optical properties of ionic liquid crystals with electrochromic admixtures

In this work we provided the investigations of electrooptical properties of liotropic ionic liquid crystals (LILC) doped with electrochromic admixture, namely with viologen. It was shown that under applying of electric field to LILC-viologen the electrochromic effect is observed. It manifests itself in colour change and in appearance of absorption bands on optical spectra. The action of the electric field also leads to the change of electric properties of the samples and to the change of parameters ofdouble electric layers existing near electrodes.

Nonlinear optical and electro-optical properties of ionic lyotropic smectics with different impurities

Metal-organic ionic smectices (MOIS) have investigated to find their photorefractive properties. For the first time the multiplexing holographic recording of permanent gratings is obtained in pure lyotropic MOIS. It is proposed new mechanism of holographic recording in ionic smectics involving photo-chemical processes associated with multi-photon absorption. Dynamic grating recording has obtained in MOIS doped by electrochromic impurity (viologen) and in ionic smectic glasses composed by decanoate Co2+. A regeneration of viologen from radical state to initial molecule state becomes the main recording mechanism in MOIS with viologen impurity. Electronic absorption of Co2+ determines the recording of dynamic gratings in the ionic smectic glasses.