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Bombard A.J.F.,Federal University of Itajubá | 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.


Dukhin A.,Dispersion Technology Inc. | Parlia S.,Dispersion Technology Inc.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2016

Ultrasound attenuation spectroscopy provides a unique means for studying various properties of complex fluids such as aggregative stability, particle size, longitudinal rheology, zeta potential, etc. Additionally, ultrasound emerges as an important tool for microfluidics. These features of ultrasound attenuation spectroscopy are dependent upon a theory that describes colloidal particle motion in an ultrasound field. Here we verify experimentally the validity of this well-known theory at elevated temperatures. We measured the attenuation frequency spectra for a stable dispersion of alumina particles (300 nm) at different temperatures from 25 °C to 50 °C. Temperature variation affects water viscosity, which is a key parameter in said theory. We have demonstrated that the theory accounts for such dependence accurately, because critical hydrodynamic relaxation frequency shifts as the theory predicts, and particle size calculated from the measured attenuation spectra remains constant over the complete temperature range. © 2016 Elsevier B.V.


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.


Dukhin A.S.,Dispersion Technology Inc. | Parlia S.,Dispersion Technology Inc.
Colloids and Surfaces B: Biointerfaces | Year: 2014

Electroacoustic spectroscopy offers a simple way for measuring the zeta potential of proteins in physiological solutions with high ionic strength. Ultrasound as a driving force does not generate the heat effects which complicate traditional electrophoretic measurements at high ionic strength. In addition, measurements can be conducted with concentrated protein dispersions without dilution, as is required by electrophoretic methods. This paper presents results for electroacoustic measurements of 5wt.% bovine serum albumin suspended in aqueous solutions. In these suspensions the proteins are not completely dissolved; they form nano-particles with a median size of about 180nm. We studied the dependence of zeta potential on ionic strength within a wide range of salt molarities, up to as high as 0.5mol/L. Dialysis was used for performing measurements at lower ionic strength range. We also conducted pH titrations of this system and titrations with Ca2+ ions. Our results agree well with published data for samples where such data is available. © 2014 Elsevier B.V.


Dukhin A.S.,Dispersion Technology Inc. | Parlia S.,Dispersion Technology Inc.
Journal of Membrane Science | Year: 2012

The goal of this paper is to show that electroacoustic spectroscopy can be used as a viable means for characterizing membranes. A novel set-up was designed for performing these experiments with a standard electroacoustic zeta potential probe typically used for measuring ζ-potential in concentrated dispersions. Calculation of zeta (ζ) potential from the measured signal was performed with a newly derived electroacoustic theory that takes into account overlap of double layers in the membrane pores (nano-filtration membrane NF 270 manufactured by Dow Chemicals).Several titrations were performed: two salt titrations with potassium chloride and copper sulfate, and pH titration in several solutions of KCl. In all these experiments, changes in ionic environment caused changes in the ζ-potential within the pores of the membrane, as was measured by changes in electroacoustic current. In all cases the results were consistent with theoretical expectations based on prior research and knowledge of ion effects on ζ-potential.Lastly, differences in electroacoustic signal from one area of the membrane to the next (all of the same material) shed some light into the homogeneity of the membrane itself. © 2012 Elsevier B.V.


Dukhin A.,Dispersion Technology Inc. | Parlia S.,Dispersion Technology Inc.
Current Opinion in Colloid and Interface Science | Year: 2013

This paper begins with a review of the studies dedicated to the electrochemistry of non-polar liquids performed during last century. There is a list of dozens of liquids that have been studied, as well as variety of electrolytes. There is an overview of 13 different experimental methods which have been employed for this task. The theoretical part of the review emphasizes the work done by Onsager, Debye, Fuoss, Kraus, Bjerrum and others in 1920s and 30s. They initiated and justified the fundamental ideas that serve as the scientific basis for modern handbooks on non-aqueous electrochemistry. Many of these papers from 1930s and later are reviewed here. The second part of this paper is dedicated to the electrochemistry of non-polar liquids containing surfactants. These substances can serve as electrolytes if ionic. However, their main function is to enhance the solvation of ions, providing steric stabilization that minimizes ion re-association and ion-pair formation. Consequently, the classical "dissociation model" requires some modification when applied to surfactant solutions. There are also two additional theoretical models suggested specifically for surfactant solutions in non-polar liquids: the "disproportionation model" for dry inverse micelles, and the "fluctuation model" by Eicke, Borkovec, and Das-Gupta for microemulsions. Charged microemulsion droplets can serve as ions, which justifies the inclusion of this theory in this review. In addition, we can study (with a well defined theory) the transition from microemulsion droplet to dry inverse micelle ion by reducing water content. Studying this transition reveals some important features of both systems. We present here these three theories and apply them for interpreting experimental data (mostly conductivity) in four different systems, all of which are non-polar systems containing surfactants: solutions of ionic surfactants, solutions of non-ionic surfactants, microemulsions with ionic surfactants, and microemulsions with non-ionic surfactants. © 2013 Elsevier Ltd.


Dukhin A.,Dispersion Technology Inc. | Parlia S.,Dispersion Technology Inc.
Journal of the Electrochemical Society | Year: 2015

We have measured the conductivity of binary alcohol-toluene mixtures (using 8 different alcohols) across the entire concentration range. The conductivity varies from 10-11 up to 3.10-4 S/m and, for a certain range decays rapidly and non-linearly with decreasing alcohol content.We assume that this range is associated with ion-pair formation due to decrease in dielectric constant. The Onsager-Fuoss conductivity theory is unable fit experimental conductivity across such wide range. Because of this we have suggested a more general conductivity theory that is based on the known expression for ionic strength, which has been derived directly from mass-action law for ion/ion-pair equilibrium (Aurbach [1999]). This theory fits experimental conductivity for all mixtures, for data which spans over 7 orders of magnitude. The adjustable parameters in this general theory are total ion concentration in the pure alcohol, the shortest distance of ion approach in the ion-pair, and hydrodynamic size of the ions. © 2015 The Electrochemical Society.


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.


Patent
Dispersion Technology Inc. | Date: 2010-08-23

Propagation of ultrasound through a porous body saturated with liquid generates electric response.


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.

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