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Ravera F.,CNR Institute of Neuroscience | Loglio G.,University of Florence | Kovalchuk V.I.,NASU F. D. Ovcharenko Institute of Biocolloidal Chemistry
Current Opinion in Colloid and Interface Science | Year: 2010

Dilational rheology represents a powerful tool to investigate equilibrium and dynamic properties of simple and more complex interfacial layers containing surfactants, proteins, polymers or micro-nano sized particles. Concerning the experimental techniques for dilational rheology, drop/bubble tensiometers based on the acquisition of the drop/bubble profile and capillary pressure tensiometers are especially effective.This article focuses on oscillating drop/bubble methodologies where harmonic variations of the interfacial area are utilized for the measurement of the dilational viscoelasticity in the frequency domain. The increasing efficiency of these techniques of the last ten years is due, from one side, to the implementation of advanced instrumentations which make faster the drop/bubble control and the data acquisition and, on the other side, to the application of new theoretical approaches for data acquisition and interpretation.A critical analysis of such drop/bubble instruments is presented where their potentialities and limitations are underlined. Moreover, recent improvements in the definition of calculation methods based on the modelling of the experimental set up are reviewed together with some examples of experimental studies based on the utilisation of such methodologies. © 2010 Elsevier Ltd.

Rulyov N.N.,NASU F. D. Ovcharenko Institute of Biocolloidal Chemistry
Transactions of the Institutions of Mining and Metallurgy, Section C: Mineral Processing and Extractive Metallurgy | Year: 2016

A theory of combined microflotation is proposed which reasonably accurately describes the kinetics of fine particles flotation utilising small quantities of fine bubbles in combination with the coarse bubbles. The theory has been applied to analyse the experimental findings of fine quartz flotation by the method of combined microflotation. The theory predicts the capture efficiency of particles and fine bubbles by the coarse bubbles and the efficiency of hetero-aggregation of particles and fine bubbles in the non-uniform hydrodynamic field of a flotation cell. It is shown that the optimal size of the fine bubbles increases approximately linearly with increase of the size of particles and diameter of the coarse bubbles; the dependence on the size of particles is stronger than on the diameter of the coarse bubbles. A theoretical explanation is offered for the linear dependence of the combined microflotation rate constant on the volume dosage of fine bubbles per weight unit of solids. © 2016 Institute of Materials, Minerals and Mining and The AusIMM.

Kovalchuk N.M.,Loughborough University | Kovalchuk N.M.,NASU F. D. Ovcharenko Institute of Biocolloidal Chemistry | Trybala A.,Loughborough University | Starov V.M.,Loughborough University
Current Opinion in Colloid and Interface Science | Year: 2014

Recent developments in the studies of evaporation of liquid droplets placed on a solid substrate are reviewed for the droplet size typically larger than 1. μm, so that kinetics effects of evaporation are neglected. The attention is paid to the limits of applicability of classical diffusion model of evaporation, effect of substrate, evaporation of complex fluids and applicability for its description of the theory developed for pure liquids, and hydrothermal waves accompanying evaporation. © 2014.

Pimienta V.,Toulouse 1 University Capitole | Brost M.,Toulouse 1 University Capitole | Kovalchuk N.,NASU F. D. Ovcharenko Institute of Biocolloidal Chemistry | Bresch S.,Florida State University | Steinbock O.,Florida State University
Angewandte Chemie - International Edition | Year: 2011

Generation of cohesive motion was observed during the dissolution of mm-sized drops of dicholoromethane into aqueous surfactant solutions. This system shows pulsating drops, multi-armed rotors, and polygonal shapes. The sharp tips of these patterns eject much smaller droplets to form expanding halos or swirling chains. The daughter droplets also undergo cascades of secondary and higher-order splitting events. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kovalchuk N.M.,NASU F. D. Ovcharenko Institute of Biocolloidal Chemistry | Kovalchuk N.M.,Max Planck Institute of Colloids and Interfaces | Starov V.M.,Loughborough University
Advances in Colloid and Interface Science | Year: 2012

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. © 2011 Elsevier B.V.

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