Structurization of ferrofluids in the absence of an external magnetic field

Structural transformations in a model ferrofluid in the absence of an external magnetic field have been theoretically studied. The results agree with well-known laboratory experiments and computer simulations in showing that, if the concentration of particles and their magnetic interaction energy are below certain critical values, most particles form separate linear chains. If these parameters exceed the critical values, most particles concentrate so as to form branched network structures. The passage from chains to network has a continuous character rather than represents a discontinuous first-order phase transition. © Pleiades Publishing, Inc., 2013

Shear thickening of dense suspensions due to energy dissipation in lubrication layers between particles

This paper deals with a theoretical study of the shear thickening effects in concentrated suspensions of non-Brownian particles. Our analysis shows that an increase of the shear rate of the suspension flow leads to a decrease of the mean thickness of the gaps between the nearest particles in dense suspensions. In turn, this leads to the growth of energy dissipation in these gaps, which means an increase of the suspension effective viscosity with the shear rate. © 2013 American Physical Society

KINETICS AGGREGATION OF MAGNETIC SUSPENSIONS

International audienceWe present results of theoretical and computer study of the kinetics of chain-like aggregate formation in suspensions of non-Brownian magnetizable particles. An analytical model for calculation of the time-dependent function of distribution over chain size is suggested. This model describes the evolution of the chain structure due to the chain-chain aggregation. In order to verify this model we have compared it with the results of computer simulations of two-dimensional model of this suspension. Results of computer simulations and of the analytical model are in reasonable agreement up to 5% of the surface concentration of the particles

Heat exchange within the surrounding biological tissue during magnetic hyperthermia

The paper deals with mathematical modeling and theoretical study of the heat distribution within the surrounding biological tissue during the effect of the magnetic hyperthermia. The mathematical model is formulated and solved numerically by using the finite difference method. The intensity of heat production is used in the present model. The obtained results allow predicting the temperature change in tumor as well as in the surrounding tissue depending on intensity of the tumor heating. © 2020 International Information and Engineering Technology Association.Russian Foundation for Fundamental Investigations, RFFI: 18-08-00178, 19-52-45001Ministry of Science and Higher Education of the Russian FederationThis paper has been supported by RFFI, grants 18-08-00178, 19-52-45001 and the state program of the Ministry of Science and Higher Education of the Russian Federation (theme “Magnet” and Contract No. 02.A03.21.006)

Kinetics of internal structures growth in magnetic suspensions

The kinetics of aggregation of non Brownian magnetizable particles in the presence of a magnetic field is studied both theoretically and by means of computer simulations. A theoretical approach is based on a system of Smoluchowski equations for the distribution function of the number of particles in linear chain-like aggregates. Results obtained in the two dimensional (2D) and three dimensional (3D) models are analyzed in relation with the size of the cell, containing the particles, and the particle volume fraction φ. The theoretical model reproduces the change of the aggregation kinetics with the size of the cell and with the particle volume fraction as long as the lateral aggregation of chains is negligible. The simulations show that lateral aggregation takes place when, roughly, φ2D>5% and φ3D>1.5%. Dependence of the average size of the chains with time can be described by a power law; the corresponding exponent decreases with the particle volume fraction in relation with the lateral aggregation. In the 3D simulations, dense labyrinthine-like structures, aligned along the applied field, are observed when the particle concentration is high enough (φ3D>5%). © 2012 Elsevier B.V. All rights reserved

Studying effectiveness of the European and Eurasian Economic Union food safety legislation

The article provides a comparative analysis of the legislation on food safety in the European Union (EU) and in the Eurasian Economic Union (EAEC). Participation of national producers in global trade is limited by the different national requirements and regulations relevant to the exports and imports of food products. A new technical regulation system is being developed within the framework of the EAEC, with the aim of regulatory harmonization with international requirements. In this respect, a comparison of the requirements of EU food legislation and the EAEC to food safety is of particular interest. Within EAEC the work has been actually completed with the participation of Kazakhstan on unification of technical regulation system particularly in the food industry with other countries of the Russian Federation and Belarus.peer-reviewe

Kinetics Aggregation of Magnetic Suspensions

We present results of theoretical and computer studies of the kinetics of chain-like aggregate formation in suspensions of non-Brownian magnetizable particles. An analytical model for calculation of the time-dependent function of distribution over chain size is suggested. This model describes the evolution of the chain structure due to the chainchain aggregation. In order to verify this model we have compared it with the results of computer simulations of a two-dimensional model of this suspension. Results of computer simulations and of the analytical model are in reasonable agreement up to 5% of the surface concentration of the particles. © 2011 Elsevier B.V. All rights reserved.This work has been supported grants of the Russian Agency of Education 2.1.1/2571 and 2.1.1/1535, grants of the Russian Federal Target Program 02.740.11.0202, No. 02-740-11-5172 and NK-43P(4); grants of the Russian Fund of Fundamental Investigations 10-01-96002-Ural, 10-02-96001, 10-02-00034

Theoretical Study of the Magnetization Dynamics of Nondilute Ferrofluids

The paper is devoted to the theoretical investigation of the magnetodipolar interparticle interaction effect on magnetization dynamics in moderately concentrated ferrofluids. We consider a homogenous (without particle aggregates) ferrofluid consisting of identical spherical particles and employ a rigid dipole model, where the magnetic moment of a particle is fixed with respect to the particle itself. In particular, for the magnetization relaxation after the external field is instantly switched off, we show that the magnetodipolar interaction leads to the increase of the initial magnetization relaxation time. For the complex ac susceptibility χ (ω) = χ′ (ω) +i χ″ (ω) we find that this interaction leads to an overall increase of χ″ (ω) and shifts the χ″ (ω) peak towards lower frequencies. Comparing results obtained with our analytical approach (second order virial expansion) to numerical simulation data (Langevin dynamics method), we demonstrate that the employed virial expansion approximation gives a good qualitative description of the ferrofluid magnetization dynamics and provides a satisfactory quantitative agreement with numerical simulations for the dc magnetization relaxation, up to the particle volume fraction ∼10%, and for the ac susceptibility, up to 5%. © 2009 The American Physical Society.This work has been done under the financial support of RFFI, Grants No. 06-01-00125, No. 07-02-00079, No. 07-01-960769Ural, No. 08-02-00647, Fund CRDF, No. PG07-005-02

Towards a theory of mechanical properties of ferrogels. Effect of chain-like aggregates

The paper deals with theoretical study of deformation of a ferrogel filled by magnetizable particles united in the chain-like aggregates. The sample is placed in a magnetic field parallel to the chains. Uniaxial elongation of the sample along the field is studied. Analysis shows that interaction of the particles in the chains and rupture of the chains by the elastic forces lead to non linear dependence of the macroscopical stress on the elongation strain. The theoretical results are in principle agreement with known experimental study of the ferrogels deformation. © 2016 Published by Elsevier B.V