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Bombard A.J.F.,Federal University of Itajuba | Dukhin A.,Dispersion Technology Inc.
Langmuir | Year: 2014

Nonpolar liquids whose dielectric permittivities are close to 2 have very low conductivities, usually below 10 × 10-10 S/m. Their ionization is suppressed by the lack of solvation resulting from the negligible dipole moment of such liquids' molecules. Ionization could be enhanced by the addition of other substances that could serve as solvating agents, creating inverse micelles around ions and preventing them from reassociating into ion pairs and neutral molecules. Surfactants are normally used for this purpose, but we show here that alcohols could perform a similar function. However, the mechanism of ionization by alcohols turns out to be quite different compared to the mechanism of ionization by surfactant. For instance, the conductivity of poly-α-olefin oil (PAO) depends on the concentration of added octanol (alcohol) as an exponential function above 10% of the octanol content. At concentrations below approximately 10%, octanol does not affect the conductivity at all. This phenomenon has never been observed for surfactant solutions. Apparently, octanol is completely dissolved at concentrations below 10% and forms micelles only above this concentration, which is the cmc for octanol-PAO mixtures. Below the cmc, octanol molecules do not dissociate, despite being able to dissociate in pure octanol, which has a conductivity of about 10 × 10-7 S/m. This again stresses the importance of the solvating factor in the ionization of liquids. Above 10% concentration, octanol molecules form micelles, which become charged by the disproportionation mechanism when they collide. To explain the exponential dependence of conductivity on octanol content, we assume that charged micelles grow in volume with increasing octanol content faster than neutral ones. Ion-dipole interactions are responsible for the preferential adsorption of octanol molecules onto charged micelles. Additional ionization occurs in such larger micelles, which then break down into smaller ones carrying individual electric charges. © 2014 American Chemical Society. Source

Dukhin A.,Dispersion Technology Inc.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2013

Electroacoustic measurement of the seismoelectric current generated by ultrasound in wetted porous materials yields information on pore size in certain situations. This occurs when electric double layers inside the pore overlap or when the pore size is sufficiently large that for a given frequency the hydrodynamic flow cannot achieve a steady Pousille profile inside of the pores. Indeed, we show experimentally that magnitude and phase of the seismoelectric current become pore size dependent in such systems. Calculations of pore size from such experimental raw data requires information concerning the porosity of the material. We suggest using high frequency conductivity measurement of the porous material to determine a formation factor'', which is the ratio of the wetted porous material conductivity to the conductivity of a equilibrium supernate. Porosity calculations from the formation factor can be done by applying the Maxwell-Wagner theory. We provide experimental verification that this theory can be applied for porous materials. © 2013 Elsevier B.V. Source

Dukhin A.S.,Dispersion Technology Inc. | Shilov V.N.,NASU F. D. Ovcharenko Institute of Biocolloidal Chemistry
Journal of Colloid and Interface Science | Year: 2010

Propagation of ultrasound waves through a porous body saturated with liquid generates an electric response. This electroacoustic effect is called the " seismoelectric current" ; the reverse phenomenon, where an electric field is the driving force, is known as the " electroseismic current" The seismoelectric current can be measured with existing electroacoustic devices that were originally designed to characterize liquid dispersions. The versatility of electroacoustic devices allows them to be calibrated using dispersions and then applied to the characterization of porous bodies. Here, we present the theory of the seismoelectric effect, which we derived by following the path suggested 65. years ago by Frenkel. To verify this theory, we measured the seismoelectric current generated by sediments of micrometer-sized silica particles. We demonstrated that the measurement allowed the determination of porosity of the sediment and the calculation of the ζ-potential. The ζ-potential value, calculated using the suggested theory, closely agreed with the value independently measured for moderately concentrated dispersions using a well-known electroacoustic theory for dispersions. Measurements of the seismoelectric effect with existing electroacoustic probes open up new ways for characterizing the porosity and ζ-potential of porous bodies, including ones with low permeability. © 2010 Elsevier Inc. Source

Dukhin A.,Dispersion Technology Inc.
Electrophoresis | Year: 2014

It is known that nonpolar liquids can be ionized by adding surfactants, either ionic or nonionic. Surfactant molecules serve as solvating agents, building inverse micelles around ions, and preventing their association back into neutral molecules. According to the Bjerrum-Onsager-Fuoss theory, these inverse micelle ions should form "ion pairs." This, in turn, leads to nonlinear dependence of the conductivity on the concentration. Surprisingly, ionic surfactants exhibit linear conductivity dependence, which implies that these inverse micelle ions do not form ion pairs. Theory predicts the existence of two ionic strength ranges, which are separated by a certain critical ion concentration. Ionic strength above the critical one is proportional to the square root of the ion concentration, whereas it becomes linear below the critical concentration. Critical ion concentration lies within the range of 10-11-10-7 mol/L when ion size ranges from 1 to 3 nm. Critical ion concentration is related, but not equal, to a certain surfactant concentration (critical concentration of ion-pairs formation (CIPC)) because only a fraction of the surfactant molecules is incorporated into the micelles ions. The linear conductivity dependence for ionic surfactants indicates that the corresponding CIPC is above the range of studied concentrations, perhaps, due to rather large ion size. The same linearity is a sign that charged inverse micelles structure and fraction are concentration independent due to strong charge-dipole interaction in the charge micelle core. This also proves that CIPC is independent of critical concentration of micelle formation. Nonionic surfactants, on the other hand, exhibit nonlinear conductivity dependence apparently due to smaller ion sizes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Dukhin A.S.,Dispersion Technology Inc. | Ulberg Z.R.,NASU F. D. Ovcharenko Institute of Biocolloidal Chemistry | Karamushka V.I.,University of Educational Management | Gruzina T.G.,NASU F. D. Ovcharenko Institute of Biocolloidal Chemistry
Advances in Colloid and Interface Science | Year: 2010

Experimental evidence collected more than 20 years ago in different laboratories suggests that the interactions between live biological cells and micro- and nanoparticles depend on their metabolic state. These experiments were conducted by reputable groups, led by prominent leaders such as H. Pohl of the USA, who was the inventor of dielectrophoresis, and B. Derjaguin of the Soviet Union who was the leading author of DLVO theory. The experiments had been mostly conducted with microparticles in the early 1980s. In the early 1990s, Ukrainian researchers showed that the interaction of live cells with gold nanoparticles consisted of an initial reversible step that also depended on cell metabolism. They found indirect evidence that the ion pumps of the cells were responsible for the reversible step. Ion pumps generate a transmembrane potential, a measurable and widely-used characteristic of the cell's energetic state. The transmembrane potential, in turn, strongly affects the ζ-potential, as was experimentally discovered 40 years ago by several independent groups using cell electrophoresis. This relationship should be taken into account when DLVO theory is considered as the basis for describing the interactions between live cells and micro- and nanoparticles. Unfortunately, detail theoretical analysis indicates that such modification would not be sufficient for explaining observed peculiarities mentioned above. That is why distinguished theoreticians such as Pohl, Frohlich, Derjaguin and others have suggested three theoretical models, presumably to explain these experiments. These theoretical models should be considered to be complementary to the well-established concepts developed on this subject in the molecular biology of cells and cell adhesion. This paper is not a revision of the existing models. It is an overview of the old and forgotten experimental data and discussion of the suggested theoretical models. The unusual interaction mechanisms are only specific for live biological cells and serve a dual role: either as a first barrier to protect the cell from potentially damaging, dispersed particulates, or as a means of accumulating useful substances. Both functions are critical for the modern problem of nanotoxicology. © 2010 Elsevier B.V. All rights reserved. Source

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