Publications on the project |
063 063 063 Wetting instabilities in Langmuir-Blodgett film deposition |
Authors: | V.I. Kovalchuk, E.K. Zholkovskiy, M.P. Bondarenko, D. Vollhardt | |
Summary: | | |
Keywords: | | |
Edition: | Surfactant Science and Technology: Retrospects and Prospects, L. Romsted (Ed.), CRC Press/Taylor and Francis Group, Boca Raton | | | 2014,
193-212,English |
063 063 Theory of Broadband Dispersion of Permittivity of Biological Cell Suspensions. Kolloidnyi Zhurnal |
Authors: | V.N. Shilov,Yu.B. Borkovskaya | |
Summary: | The classical Pauly–Schwan electrical model of the biological cell is generalized by considering the diffusion processes that occur due to the selective (with respect to ions of different signes of charges) conductivity of surface cell structures (cytoplasmic membrane and electrical double layer). The analytical theory of the dispersion of the permittivity of biological cell suspensions that cover a broad frequency band that includes three typical (for these systems) dispersion regions α, β, and γ is constructed using the generalized model, whereas the classical model describes only β and γ regions. Very large values of permittivity and their complete stipulation by the ionic selectivity of surface structures, which are characteristic for the region of α dispersion, predetermine the unique sensitivity of low_frequency dielectric spectrum to the effective conductivity of the membrane of a living cell, which can find important applications in biology and medicine. | |
Keywords: | Pauly–Schwan electrical model , biological cell , dispersion of the permittivity | |
Edition: | Kolloidnyi Zhurnal,, 72, N2 | | | 2010,
173-183,Russian |
063 Membrane_Potential_Induced Electroporation as a Physical Mechanism for Metal Nanoparticle Penetration through a Cell Membrane |
Authors: | Z. R. Ulberg and V. N. Shilov | |
Summary: | A mechanism of the penetration of nanosized metal particles from an ambient solution into the cytoplasm of a living cell, has been proposed. The driving force of this new mechanism is membrane potential, i.e., the potential difference between the cellular cytoplasm and the ambient solution. The essence of the mechanism consists in the fact that a metal particle occurring at a cell membrane shunts the potential drop in the diffuse part of the electrical double layer of the membrane. As a result, almost the entire membrane potential, which, at a normal state of the cell, is distributed between its electrical double layer and the lipid bilayer of the cell membrane, appears to be completely applied to the latter. As a consequence, the field strength in the lipid bilayer rises, thereby increasing the probability of the formation of a pore in it, through which a metal particle with a diameter lying in a certain range (in the case under consideration, from two to
three tens of nanometers) can penetrate into the cytoplasm without inflicting any damage on the cell.
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Keywords: | membrane_potential, electroporation, metal nanoparticle, electrical double layer , lipid bilayer | |
Edition: | Colloid Journal, 2014, Vol. 76, No. 6 | | | 2014,
739–745,Russian |
063 Ions redistribution and meniscus relaxation during Langmuir wetting process |
Authors: | В.І. Ковальчук, М.П. Бондаренко, Е.К. Zholkovskiy, В.М. Старов, Д. Вольхардт | |
Summary: | Nonstationary kinetics of the ion redistribution within the meniscus region during deposition of a charged Langmuir monolayer after beginning or stopping of the substrate motion is analyzed on the basis of the results of numerical simulations. The time evolution of the ions concentration profiles forming at the contact line and propagating toward the bulk solution is considered. It is shown that the diffusion front propagates much slower within the region of overlapping diffuse layers than outside of this region. At the beginning of the deposition process a region characterized by quasi-stationary behavior of the ion concentration and electric potential distributions is formed in close vicinity to the contact line. A stationary deposition regime is established when the region of quasi-stationary distributions reaches the external boundary of the Nernst layer provided that the substrate motion is not very fast. For the substrate velocities higher than the critical one the concentration near the contact line can decrease to such small values which do not allow a stable deposition process. The developed mathematical model allows addressing to transient regimes of the monolayer deposition which are very important for understanding the mechanisms leading to meniscus instability. | |
Keywords: | Non-stationary kinetics, meniscus instability, deposition, Langmuir monolayer, Nernst layer | |
Edition: | J. Phys. Chem. B, 115 | | | 2011,
1999–2005,Belarusian |
063 Coupled concentration polarization and electroosmotic circulation near micro/nano-interfaces: Taylor-Aris model of hydrodynamic dispersion and limits of its applicability |
Authors: | A. Yaroshchuk, E. Zholkovskiy, S. Pogodin and V. Baulin | |
Summary: | Mismatches in electrokinetic properties between micro- and nanochannels give rise to superposition of electroosmotic and pressure-driven flows in the microchannels. Parabolic or similar flow profiles are known to cause the so-called hydrodynamic dispersion, which under certain conditions can be formally assimilated to an increase in the solute diffusivity (Taylor–Aris model). It is demonstrated theoretically that taking into account these phenomena modifies considerably the pattern of current-induced concentration polarization of micro/nanointerfaces as compared to the classical model of unstirred boundary layer. In particular, the hydrodynamic dispersion leads to disappearance of limiting current. At essentially “over-limiting” current densities, the time-dependent profiles of salt concentration in microchannels behave like sharp concentration “fronts” moving away from the interface until they reach the reservoir end of the microchannel. Under galvanostatic conditions postulated in this study, these “fronts” move with practically constant speed directly proportional to the current density. The sharp transition from a low-concentration to a high-concentration zone can be useful for the analyte preconcentration via stacking. The pattern of moving sharp concentration “fronts” has been predicted for the first time for relatively broad microchannels with negligible surface conductance. The Taylor–Aris approach to the description of hydrodynamic dispersion is quantitatively applicable only to the analysis of sufficiently “slow” processes (as compared to the characteristic time of diffusion relaxation in the transversal direction). A posteriori estimates reveal that the condition of “slow” processes is typically not satisfied close to current-polarized micro/nanointerfaces. Accordingly, to make the description quantitative, one needs to go beyond the Taylor–Aris approximation, which will be attempted in future studies. It is argued that doing so would make even stronger the dampening impact of hydrodynamic dispersion on the current-induced concentration polarization of micro/nanointerfaces. | |
Keywords: | Taylor–Aris approximationhy , hydrodynamic dispersion, nanochannels | |
Edition: | Langmuir, 27 | | | 2011,
11710-11721,English |
063 Aggregation in colloidal suspensions: Effect of colloidal forces and hydrodynamic interactions |
Authors: | N.M. Kovalchuk, V.M. Starov | |
Summary: | The forces acting in colloidal suspensions and affecting their stability and aggregation kinetics are considered. The approximations used for these forces in numerical simulations and the importance of the balanced account for both colloidal forces and hydrodynamic interactions are discussed. As an example the results of direct numerical simulations of kinetics of aggregation either with account for hydrodynamic interaction between particles or without it are compared by varying the parameters of the interaction potential between particles and fraction of solid. Simulations are based on the Langevin equations with pairwise interaction between particles and take into account Brownian, hydrodynamic and colloidal forces. It is confirmed that the neglecting of hydrodynamic interaction results in an accelerated growth of aggregates. The results of numerical simulations of aggregation kinetics are compared with well known analytical solutions. | |
Keywords: | stability , aggregation kinetics , numerical simulation | |
Edition: | Adv. Colloid Interface Sci. | | | 2012,
99–106,English |
063 Electrophoresis and Stability of Nano-Colloids: History, Theory and Experimental Examples |
Authors: | C. Felix, A. Yaroshchuk, B.G. Pollet, S. Pasupathi, M.P. Bondarenko, V.I. Kovalchuk and E.K. Zholkovskiy | |
Summary: | The paper contains an extended historical overview of research activities focused on determining interfacial potential and charge of dispersed particles from electrophoretic and coagulation dynamic measurements. Particular attention is paid to nano-suspensions for which application of Standard Electrokinetic Model (SEM) to analysis of experimental data encounters difficulties, especially, when the solutions contain more than two ions, the particle charge depends on the solution composition and zeta-potentials are high. Detailed statements of Standard Electrokinetic and DLVO Models are given in the forms that are capable of addressing electrophoresis and interaction of particles for arbitrary ratios of the particle to Debye radius, interfacial potentials and electrolyte compositions. The experimental part of the study consists of two groups of measurements conducted for Pt/C nano-suspensions, namely, the electrophoretic and coagulation dynamic studies, with various electrolyte compositions. The obtained experimental data are processed by using numerical algorithms based on the formulated models for obtaining interfacial potential and charge. While analyzing the dependencies of interfacial potential and charge on the electrolyte compositions, conclusions are made regarding the mechanisms of charge formation. It is established that the behavior of system stability is in a qualitative agreement with the results computed from the electrophoretic data. The verification of quantitative applicability of the employed models is conducted by calculating the Hamaker constant from experimental data. It is proposed how to explain the observed variations of predicted Hamaker constant and its unusually high value.
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Keywords: | Standard Electrokinetic Model , DLVO Models , Pt/C nano-suspensions | |
Edition: | Adv. Colloid Interface Sci., 2014, 211 | | | 2012,
77–92,English |
063 Mechano-Chemical Effects in Weakly Charged Porous Media |
Authors: | E.K. Zholkovskij, A.E. Yaroshchuk, V.I. Kovalchuk, M.P. Bondarenko | |
Summary: | The paper is concerned with mechano-chemical effects, namely, osmosis and pressure‐driven separation of ions that can be observed when a charged porous medium is placed between two electrolyte solutions. The study is focused on porous systems with low equilibrium interfacial potentials (about 30 mV or lower). At such low potentials, osmosis and pressure‐driven separation of ions noticeably manifest themselves provided that the ions in the electrolyte solutions have different diffusion coefficients.
The analysis is conducted by combining the irreversible thermodynamic approach and the linearized (in terms of the normalized equilibrium interfacial potential) version of the Standard Electrokinetic Model. Osmosis and the pressure‐driven separation of ions are considered for an arbitrary mixed electrolyte solution and various porous space geometries. It is shown that the effects under consideration are proportional to a geometrical factor which, for all the considered geometries of porous space, can be expressed as a function of porosity and the Λ- parameter of porous medium normalized by the Debye length. For all the studied geometries, this function turns out to be weakly dependent on both the porosity and the geometry type. The latter allows for a rough evaluation of the geometrical factor from experimental data on electric conductivity and hydraulic permeability without previous knowledge of the porous space geometry.
The obtained results are used to illustrate how the composition of electrolyte solution affects the mechano-chemical effects. For various examples of electrolyte solution compositions, the obtained results are capable of describing positive, negative and anomalous osmosis, positive and negative rejection of binary electrolytes, and pressure‐driven separation of binary electrolyte mixtures. | |
Keywords: | osmosis , pressure‐driven separation of ions, charged porous medium | |
Edition: | Adv. Colloid Interface Sci., available online 2 October 2014, DOI: 10.1016/j.cis.2014.09.006 | | | 2014,
,English |
The events in the framework of the project |
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063 2.4. Colloidal nanoscale systems Purpose: Expected results:Issue of new types of products: methods, theories Stage 1:Розробка математичних формалізмів, здатних описувати електро-механо-хімічні явища у нано-структурованих пористих середовищах та Ван дер Ваальсові взаємодії в концентрованих суспензіях нано-частинок. Stage 2:Розробка теорії осмотичного тиску та стійкості в концентрованих суспензіях нано-частинок та електро- гідродинамічних явищ, що спостерігаються в перехідній зоні між мікро- та нано-пористими середовищами. Stage 3:Дослідження впливу непарних взаємодій на кинетику коагуляції суспензій нано-частинок та отримання матриці кінетичних коефіцієнтів, що описують електро-механо-хімічні перетворення у нано-структурованих пористих середовищах. Stage 4:Дослідження динаміки утворення та розпаду дублетів з нано-розмірних частинок та обчислення основних параметрів процесу електро – хроматографічного розділення не-електролітів. Stage 5:Дослідження геометрії коагуляційних нано-структур та обчислення основних параметрів процесу електро – хроматографічного розділення електролітів
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