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Aleksey M. Tikhonov

Publications and source records attributed to Aleksey M. Tikhonov.

At least 19 recordsLinked to original sources
arXiv2020

Prospects for the Use of Laboratory Sources for X-ray Reflectometry of Thin Films on a Liquid Surface

The authors present a review of the systematic studies of the structure of macroscopically planar thin films at the air-liquid interface (water, alkali solution and silica hydrosol). A common feature of the considered works is the application of a model-independent approach to the analysis of X-ray reflectometry data, which does not require a priori assumptions about the structure of the object under study. It is shown that the experimental results obtained with the laboratory source in some cases are qualitatively on par with the results of those obtained with the use of synchrotron radiation source. The reproducibility of the effect of spontaneous ordering in films of amphiphilic organic molecules (phospholipids) at the surface of the colloidal solution of silica nanoparticles is demonstrated. The possibility of influencing the kinetics of the in situ formation of a phospholipid film by enriching the liquid substrate with alkali metal ions is also discussed.

cond-mat.soft↗
arXiv2020

Synchrotron X-Ray Reflectivity Study of the Adsorption Film of Octadecanamide at the Toluene-Water Interface

The structure of an adsorption octadecanamide film at the planar toluene-water interface is studied by X-ray reflectometry using synchrotron radiation with photon energy of 15 keV. The electron density (polarizability) profiles, according to which the interface structure is determined by the pH level in the water subphase, are reconstructed from experimental data with the help of a model-independent approach. For a high pH~11, the adsorption film is a crystalline octadecanamide monolayer with a thickness of about 2.6 nm, in which aliphatic tails of surfactant are extended along the normal to the surface. For low pH ~ 2, the thickness of the surface structure consisting of the crystalline monolayer directly on the toluene-water interface and a thick layer of deposited octadecanamide micelles reaches about 50 nm. In our opinion, the condensation of nonionogenic surfactant micelles for which the surface concentration of the surfactant increases significantly is caused by a change in the polarization direction upon a decrease in the pH level in the electric double layer at the interface between the water subphase and the octadecanamide monolayer. The shape of the reconstructed electron density profiles also indicates the existence of a plane of the closest approach of surfactant micelles to the interface at a distance of about 7 nm from it.

cond-mat.soft↗
arXiv2019

Adsorption of Polylysine on the Surface of the DMPS Monolayer

The effect of the adsorption of a polypeptide on the lateral interaction of dimyristoylphosphatidylserine molecules in different phase states on the surface of a 10\,mM KCl aqueous solution has been studied. Changes in the surface pressure and Volta potential induced by the adsorption of large poly-D-lysine molecules (about 200 links in a chain) have been determined at different areas per lipid molecule in a monolayer. The adsorption of macromolecules noticeably increases the elasticity of the monolayer under lateral compression in the liquid expanded state of lipid and reduces the effective dipole moment from 0.48 to 0.38 D. These properties are in qualitative agreement with X-ray reflectometry data for the lipid monolayer obtained with synchrotron radiation with a photon energy of 70 keV. The electron density profiles perpendicular to the surface of the aqueous subphase have been reconstructed from reflectometry data within a model approach to the structure of an interface with two and three layers. These profiles indicate the existence of a wide diffuse polymer layer 150+/-40 Angstrom in width at the interface of the monolayer in both the liquid expanded and liquid condensed states. A decrease in the area per molecule in the monolayer by a factor of 2 results in the doubling of the surface density of the macromolecule film. The adsorption of the polymer also affects the integral density of the layer of polar phospholipid groups, which decreases by a factor of ~ 2 in the liquid expanded phase and by ~ 30% in the liquid condensed phase.

cond-mat.soft↗
arXiv2018

Solid-Liquid Phase Transition in the Octadecanoic Acid Film Adsorbed on the Toluene-Water Interface

The structure of the soluble protonated (pH=2) octadecanoic acid film adsorbed on the saturated hydrocarbon (n-hexane) - water and aromatic hydrocarbon (toluene)-water interfaces is studied by X-ray reflectometry using synchrotron radiation. The experimental data demonstrate that a solid phase of a Gibbs monolayer (26 +/- 1) Angstrom thick, in which aliphatic tails are perpendicular to the surface and the area per molecule is A=(18 +/- 2) Angstrom^2, forms in the film at the n-hexane - water interface. The solid monolayer on the toluene - water interface in the adsorbed film melts when temperature increases, and this transition is caused by disordering the hydrocarbon tails of the acid. During the solid - liquid transition, the Gibbs monolayer thickness remains almost the same, (22 +/- 1) Angstrom. In the solid phase, we have A=(20+/- 2) Angstrom^2 and the angle of deviation of the molecular tails from the normal to the surface is about ~ 30 deg. The density of the liquid monolayer phase with A=(24 +/- 2) Angstrom^2 corresponds to liquid n-octadecane.

cond-mat.soft↗
arXiv2018

On the Diffuse Structure of the Toluene - Water Interface

The electric density profile along the normal to the phase interface between aromatic hydrocarbon toluene and water has been studied by X-ray reflectometry using synchrotron radiation. According to the experimental data, the width of the interface under normal conditions is (5.7 +/- 0.2) Angstrom. This value is much larger than a theoretical value of (3.9 +/- 0.1) Angstrom predicted by the theory of capillary waves with an interphase tension of (36.0 +/- 0.1) mN/m. The observed broadening of the interface is attributed to its own diffuse near-surface structure with a width no less than 4 Angstroms, which is about the value previously discussed for high-molecular-weight n-alkane - water and 1,2-dichloroethane - water interfaces.

cond-mat.soft↗
arXiv2018

Modelless X-Ray Scattering Study of a Silica Hydrosol Surface

The structure of the adsorbed layer of alkali ions on the surface of colloidal silica solutions with a particle size of ~27 nm has been studied by reflectometry and diffuse scattering of synchrotron radiation with a photon energy of about 71 keV. Electron density profiles in the direction perpendicular to the surface have been reconstructed from experimental data and spectra of the correlation function of heights in the surface plane have been obtained. The revealed deviation of the integral and frequency characteristics of the roughness spectra of the silica sol surface from predictions of the capillary-wave theory is of a fundamental character. This deviation is due to the contribution from roughnesses with low spatial frequencies and to the interference of diffuse scattering from different layer interfaces of the surface structure.

cond-mat.soft↗
arXiv2018

X-Ray Study of Thermotropic Mesophases of an n-Triacontanol Adsorption Film at the n-Hexadecane - Water Interface

Using synchrotron radiation with a photon energy of 15 keV, the molecular structure of an adsorbed n-triacontanol layer at the n-hexadecane - water interface in different its phase states has been studied by the method of diffuse X-ray scattering. The analysis of the experimental data shows that a transition to the multilayer adsorption occurs at a temperature below the two-dimensional vapor - liquid transition at the interface. This transition has been attributed to a feature in the temperature dependence of the concentration of micelles in a surface layer 100 - 200 Å thick.

cond-mat.soft↗
arXiv2017

Study of DMPS Monolayers on a Water Substrate with Laboratory X-ray Reflectometer

The molecular structure of dimyristoyl phosphatidylserine (DMPS) monolayers on a water substrate in different phase states has been investigated under normal conditions by X-ray reflectometry with a photon energy of ~ 8 keV. According to the experimental data, the transition from a two-dimensional expanded liquid state to a solid gel state (liquid crystal) accompanied by the ordering of the hydrocarbon tails of the DMPS molecule occurs in the monolayer as the surface pressure rises. The monolayer thickness is (20 +/- 3) Angstrom and (28 +/- 2) Angstrom in the liquid and solid phases, respectively, with the deflection angle of the molecular tail axis from the normal to the surface in the gel phase being (26 +/- 8) deg. At least a twofold decrease in the degree of hydration of the polar lipid groups also occurs under two-dimensional monolayer compression. The reflectometry data have been analyzed using two approaches: under the assumption about the presence of two layers with different electron densities in the monolayer and without any assumptions about the transverse surface structure. Both approaches demonstrate satisfactory agreement between themselves in describing the experimental results.

cond-mat.soft↗
arXiv2017

X-Ray Scattering near a Liquid - Vapor Phase Transition at the n-Hexane - Water Interface

The molecular structure of neutral n-triacontanol mesophases at the n-hexane - water interface has been studied by diffuse X-ray scattering using synchrotron radiation. According to the experimental data, a transition to the multilayer adsorption of alkanol occurs at a temperature below the transition from a gas phase to a liquid Gibbs monolayer.

cond-mat.soft↗
arXiv2017

Nuclear Magnetic Resonance in Noncollinear Antiferromagnet Mn3Al2Ge3O12

The 55Mn nuclear magnetic resonance spectrum of noncollinear 12-sublattice antiferromagnet Mn3Al2Ge3O12 has been studied in the frequency range of 200 - 640 MHz in the external magnetic field H || [001]} at T=1.2 K. Three absorption lines have been observed in fields less than the field of the reorientation transition Hc at the polarization h||H of the rf field. Two lines have been observed at H > Hc and h_|_H. The spectral parameters indicate that the magnetic structure of manganese garnet differs slightly from the exchange triangular 120-degree structure. The anisotropy of the spin reduction and (or) weak antiferromagnetism that are allowed by the crystal symmetry lead to the difference of approximately 3% in the magnetization of sublattices in the field H < Hc. When the spin plane rotates from the orientation perpendicular to the C3 axis to the orientation perpendicular to the C4 axis, all magnetic moments of the electronic subsystem decrease by approximately 2% from the average value in the zero field.

cond-mat.mtrl-sci↗
arXiv2017

Thermotropic Phase Transition in an Adsorbed Melissic Acid Film at the n-Hexane - Water Interface

A reversible thermotropic phase transition in an adsorption melissic acid film at the interface between n-hexane and an aqueous solution of potassium hydroxide (pH=10) is investigated by X-ray reflectometry and diffuse scattering using synchrotron radiation. The experimental data indicate that the interface "freezing" transition is accompanied not only by the crystallization of the Gibbs monolayer but also by the formation of a planar smectic structure in the ~300-Angstrom-thick adsorption film; this structure is formed by ~50-Angstrom-thick layers.

cond-mat.soft↗
arXiv2017

Kinetics of the Phospholipid Multilayer Formation at the Surface of the Silica Sol

The ordering of a multilayer consisting of DSPC bilayers on a silica sol substrate is studied within the model-independent approach to the reconstruction of profiles of the electron density from X-ray reflectometry data. It is found that the electroporation of bilayers in the field of anion silica nanoparticles significantly accelerates the process of their saturation with Na+ and H2O, which explains both a relatively small time of formation of the structure of the multilayer of 10^5 - 7x10^5 s and ~13 % excess of the electron density in it.

physics.bio-ph↗
arXiv2015

Nonlinear Absorption of Radio Waves in a Noncollinear Antiferromagnet

The nonlinear absorption of radio waves (200 - 800 MHz) in a noncollinear cubic antiferromagnet Mn3Al2Ge3O12 in an external magnetic field H || [001] has been studied in the temperature range of 1.2 - 4.2 K. We attribute the observed dissipation of the electromagnetic energy to the parametric excitation of inhomogeneous surface waves at the boundaries of antiferromagnetic domains.

cond-mat.mtrl-sci↗
arXiv2015

On the Formation of a Macroscopically Flat Phospholipid Membrane on a Hydrosol Substrate

The dependence of the structure of a phospholipid layer (DSPC and SOPC) adsorbed on a hydrosol substrate on the concentration of NaOH in a solution of 5-nm silica particles has been studied by X-ray reflectrometry with the use of synchrotron radiation. Profiles of the electron density (polarizability) have been reconstructed from the experimental data within a model-independent approach. According to these profiles, the thickness of the lipid film can vary from a monolayer (~ 35 Angstrom) to several bilayers (~ 450 Angstrom). At the volume concentration of NaOH of ~ 0.5 mol/L, the film on the hydrosol surface is a macroscopically flat phospholipid membrane (bilayer) with a thickness of ~ 60 Angstrom and with areas of 45 +/- 2 and 49 +/- 3 Angstrom^2 per DSPC and SOPC molecule, respectively.

cond-mat.soft↗
arXiv2010

A Wideband Spectrometer for NMR Studies

The design of a wideband decimeter-wave (200 - 900 MHz) spectrometer with a magnetic induction of up to ~ 10 T is described. This spectrometer is intended for studying electronic - nuclear oscillations in antiferromagnets at low temperatures (4.2 - 1.3 K). Critical field H_c = 2.5 +/- 0.3 T of a reorientation transition in a noncollinear antiferromagnet Mn3Al2Ge3O12 at temperature T = 1.3 K was determined from a 55Mn2+ NMR spectrum.

physics.ins-det↗