Biomedical subjects

NL Filippova

Publications and source records attributed to NL Filippova.

10 recordsLinked to original sources

PubMed1999

Dynamic Surface Tension and Adsorption/Desorption Kinetics for Polymer Mixtures on Planar Surfaces.

The adsorption/desorption kinetics for individual polymers and polymer mixtures of the water-soluble associative polymers with molecular weights of 12, 62, and 100 kg/mol onto a SiO2 planar substrate have been studied by ellipsometry at room temperature under flow conditions. Equations were derived to predict behaviors of the adsorption/desorption kinetics and dynamic surface tension onto planar surface for any times. It is shown that the rate of adsorption/desorption kinetics under nonflow conditions is significantly less than the one under flow conditions due to the convective-diffusive mass transfer to an interface. Copyright 1999 Academic Press.

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PubMed1999

Dynamic Surface Tension and Adsorption/Desorption Kinetics for Mixtures on Planar Surfaces: I. Under Nonflow Conditions.

The adsorption/desorption kinetics for individual polymers and polymer mixtures of the water-soluble associative polymers with molecular weights of 12, 62, and 100 kg/mol onto SiO2 planar substrate have been studied by ellipsometry at room temperature under nonflow conditions. Equations were derived to predict behaviors of the adsorption/desorption kinetics and dynamic surface tension onto planar surfaces for any times. It is shown that the desorption kinetics of the water-soluble associative polymers onto planar SiO2 surface is an irreversible process due to strong interaction between polymer molecules and an interface. Copyright 1999 Academic Press.

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PubMed1999

Interdiffusion in Polymer Film by Ellipsometry.

The long-time approximation for the time-dependence concentration of solvent into film is derived. The interdiffusion coefficients for different temperatures and the different polystyrene molecular weights were calculated by using asymptotic formulae and time-dependence concentrations of solvent into polymer films. The apparent activation energies of interdiffusion were estimated. Copyright 1999 Academic Press.

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PubMed1999

Adsorption Kinetics of Polyelectrolytes on Planar Surfaces under Flow Conditions.

The focus of our work has been to develop a theory of adsorption kinetics for polyelectrolytes in a flow cell onto planar surfaces in the framework of the two-dimensional model and to study adsorption processes of polyelectrolytes on a planar surface by ellipsometry. We have studied the adsorption kinetics of water-soluble cationic poly(vinylamine) hydrochloride homopolymer from aqueous solution onto both silicon wafers and polystyrene films by ellipsometry. Equations were derived to calculate (a) the equilibrium adsorption, (b) the thickness of the adsorbed layer, (c) the activation energy of adsorption for water-soluble polyelectrolytes, (d) the rate constant for the water-soluble polyelectrolytes, (e) the effective coefficients of diffusion in the adsorbed layer, and (f) the time needed to attain the equilibrium state for the adsorption of the water-soluble polyelectrolytes in a flow cell. Copyright 1999 Academic Press.

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PubMed1998

Kinetic-Diffusion-Controlled Adsorption and Desorption Kinetics on Planar Surfaces.

The adsorption and desorption kinetics of water-soluble associative polymers with different molecular weights on the silicon wafers were studied by ellipsometry. The parameters characterizing the adsorption and desorption processes such as (a) the maximum amount of adsorbate adsorbed, Gammainfinity, (b) the equilibrium constant, K(p), (c) the activation energy of adsorption, (-DeltaH), (d) the rate constants for adsorption and desorption processes, Kad, Kdes, (e) the coefficient of diffusion, D0, (f) the activation energy of the effective diffusion, Q, and (g) the time needed to attain the equilibrium states for the adsorption and desorption processes were calculated from the experimental ellipsometric data. It is shown that the adsorption kinetics for mixtures over a wide range of concentrations is governed by: (I) the kinetic adsorption at the interface, (II) the kinetic adsorption at the interfaces as well as simultaneous diffusion, and/or (III) diffusion. The existence of regimes (I), (II), and (III) for adsorption and desorption kinetics are justified by using the experimental data for the adsorption and desorption kinetics of water-soluble associative polymers with different molecular weights of 12, 62, and 120 kg/mol. Copyright 1998 Academic Press.

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PubMed1998

Adsorption and Desorption Kinetics with Systems Having a Concentration-Dependent Coefficient of Diffusion.

In many adsorbents, surface diffusion is the governing mechanisms of transport. The coefficient of surface diffusion may be concentration dependent. The model equations for adsorption and desorption processes controlling both the diffusive-convective mass transfer in the bulk and surface diffusion in the adsorbent have been solved for some cases for a range of parameter values which may apply for many adsorption systems. The equations to calculate (a) the surface diffusion coefficient, Di, (b) the activation energy for surface diffusion, (-DeltaH), (c) the relaxation times characterizing the adsorption and desorption processes, and (d) the times needed, tad Gamma, tdes Gamma, to reach the quasiequilibrium state for the adsorption and desorption processes are derived. Copyright 1998 Academic Press.

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PubMed1998

Adsorption and Heat of Adsorption onto Polymer Particular Surface by Inverse Gas Chromatography

A theory of nonlinear inverse chromatography for arbitrary adsorption isotherms has been developed. Methods of investigating adsorption isotherms and heat of adsorption based on the analysis of chromatograms for different temperatures are suggested. Simple formulae for calculating of adsorption isotherms and heat of adsorption are derived. The adsorption isotherm and heat of adsorption of pyridine on particular poly(imide)siloxane have been investigated by inverse chromatography. Copyright 1998 Academic Press. Copyright 1998Academic Press

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PubMed1997

Non-Langmuir Adsorption on Planar Surfaces: Nonlinear Theory and Experiment

A theory of non-Langmuir kinetics of polymer molecules on planar surfaces in the framework of the kinetic-conformational-diffusive-controlled model has been developed. It is shown that an overshoot in both the equilibrium adsorption and the adsorption kinetics may be explained using the conformational kinetics of polymer molecules on planar surfaces with the term depending on the surface polymer concentration. From the experimental data, equations were derived to calculate the equilibrium constant, K0(p), the conformational parameter beta characterizing the conformational process, the thickness of the adsorbed layer, dad.layer, the weight fraction of polymers in the adsorbed layer, Wtplat, the activation energy of adsorption, (-DeltaH), the diffusion coefficient, D(theta), the activation energy of diffusion in the adsorbed layer, Q, the relaxation time tconf characterizing the conformational process, and the time needed to attain the equilibrium state for the adsorption process. The adsorption of poly(dimethylsiloxane) on an oxide surface of silicon has been investigated by ellipsometry. Overshoots in both the equilibrium adsorption and the adsorption kinetics of poly(dimethylsiloxane) on an oxide surface of a silicon were observed. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Dynamic Surface Tension and Adsorption Kinetics from Micellar Solutions on Planar Surfaces

A qualitative theory of the dynamic surface tension and adsorption kinetics from micellar surfactant solutions on a planar surface is developed for the kinetic-diffusive-controlled adsorption process obeying any adsorption kinetics on a planar surface and any micellization-demicellization kinetics in the bulk. The time-dependent adsorption and dynamic surface tension is obtained in an analytical form for short and long times. It is shown that the adsorption process and dynamic surface tension over a wide range of surfactant (monomer) concentrations is governed by: (I) the adsorption kinetics of monomers and micelles for short times (0 </= t </= tcr1), (II) the adsorption kinetics of monomers and micelles on a planar surface and the micellization-demicellization kinetics in the bulk, and the diffusion of monomers and micelles for intermediate times (tcr1 </= t </= tcr2), and (III) the diffusion of monomers and micelles for long times (t >/= tcr2). Formulas were derived to estimate the relaxation times tcr1, tcr2, and the parameters characterizing the adsorption process over a wide range of times. The existence of the (I), (II), and (III) regimes are justified by using the experimental data for the dynamic surface tension of a micellar Brij 58 solution.

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PubMed1997

Dynamic Surface Tension and Adsorption Kinetics in Finite Systems

A quantitative theory is developed to describe the dynamic surface tension and the adsorption kinetics at a liquid-liquid interface, taking into account the molecular diffusion in both bulk phases and the adsorption isotherm for surfactant on the interface. Asymptotic analytical solutions are obtained in the following finite systems: (i) a liquid spherical drop, (ii) a liquid spherical drop surrounded by a liquid phase, and (iii) a liquid spherical drop surrounded by a spherical liquid shell. The behavior of the dynamic surface tension and interfacial adsorption over a wide range of times is predicted for cases (i) through (iii). The conditions under which the dynamic surface tension passes through a minimum below the steady state value are found. The theoretical model developed allows a qualitative interpretation of the experimental data obtained for a viscous crude oil containing natural acids after contact with aqueous alkali.

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