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Slavchov RI, Peychev B, Minkov I. Electrolytes at Uncharged Liquid Interfaces: Adsorption, Potentials, Surface Tension, and the Role of the Surfactant Monolayer. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:17170-17189. [PMID: 39132874 PMCID: PMC11340029 DOI: 10.1021/acs.langmuir.4c01388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2024] [Revised: 07/15/2024] [Accepted: 07/18/2024] [Indexed: 08/13/2024]
Abstract
The article summarizes the results of our research on the behavior of ions at uncharged fluid interfaces, with a focus on moderately to highly concentrated aqueous electrolytes. The ion-specific properties of such interfaces have been analyzed. The ion-specificity series are different for water|air and water|oil; different for surface tension σ, surface Δχ potential and electrolyte adsorption, and they change with concentration. A methodology has been developed that allows to disentangle the multiple factors controlling the ion order. The direct ion-surface interactions are not always the most significant factor behind the observed ion sequences: indirect effects stemming from conjugate bulk properties are often more important. For example, the order of the surface tension with the nature of the anion (σKOH > σKCl > σKNO3 for potassium salts) is often the result of bulk nonideality and follows the order of the bulk activity coefficients (γKOH > γKCl > γKNO3) rather than that of a specific ion-surface interaction potential. The surface Δχ potential of aqueous solutions is, in many cases, insensitive to the ion distribution in the electric double layer but reflects the orientation of water at the surface, through the ion-specific dielectric permittivity ε of the solution. Even the sign of Δχ is often the result of the decrement of ε in the presence of electrolyte. A whole new level of complexity appears when the ions interact with an uncharged surfactant monolayer. A method has been developed to measure the electrolyte adsorption isotherms on monolayers of varying area per surfactant molecule via a combination of experiments-compression isotherms and surface pressure of equilibrium spread monolayers. The obtained isotherms demonstrate that the ions exhibit a maximum in their adsorption on monolayers of intermediate density. The maximum is explained with the interplay between ion-surfactant complexation, volume exclusion and osmotic effects.
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Affiliation(s)
- Radomir Iliev Slavchov
- School
of Engineering and Materials Science, Queen
Mary University of London, London E1 4NS, United
Kingdom
| | - Boyan Peychev
- School
of Engineering and Materials Science, Queen
Mary University of London, London E1 4NS, United
Kingdom
- Rostislaw
Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
| | - Ivan Minkov
- Rostislaw
Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
- Department
of Chemistry, Biochemistry, Physiology, and Pathophysiology, Faculty of Medicine, Sofia University, 1407 Sofia, Bulgaria
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Peychev B, Arabadzhieva D, Minkov I, Mileva E, Smoukov SK, Slavchov RI. Measuring the Adsorption of Electrolytes on Lipid Monolayers. J Phys Chem Lett 2023; 14:4652-4656. [PMID: 37167099 DOI: 10.1021/acs.jpclett.3c00795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The interactions between ions and lipid monolayers have captivated the attention of biologists and chemists alike for almost a century. In the absence of experimentally accessible concentration profiles, the electrolyte adsorption remains the most informative quantitative characteristic of the ion-lipid interactions. However, there is no established procedure to obtain the electrolyte adsorption on spread lipid monolayers. As a result, in the literature, the ion-lipid monolayer interactions are discussed qualitatively, based on the electrolyte effect on more easily accessible variables, e.g., surface tension. In this letter, we demonstrate how the electrolyte adsorption on lipid monolayers can be obtained experimentally. The procedure requires combining surface pressure versus molecular area compression isotherms with spreading pressure data. For the first time, we report an adsorption isotherm of NaCl on a lipid monolayer as a function of the density of the monolayer. The leading interactions seem to be the osmotic effect from the lipid head groups in the surface layer and ion-lipid association.
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Affiliation(s)
- Boyan Peychev
- Queen Mary University of London, School of Engineering and Materials Science, Mile End Road, London E1 4NS, United Kingdom
| | - Dimitrinka Arabadzhieva
- Rostislaw Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 11, 1113 Sofia, Bulgaria
| | - Ivan Minkov
- Rostislaw Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 11, 1113 Sofia, Bulgaria
- Department of Chemistry, Biochemistry, Physiology, and Pathophysiology, Faculty of Medicine, Sofia University, 1 Koziak Str., 1407 Sofia, Bulgaria
| | - Elena Mileva
- Rostislaw Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 11, 1113 Sofia, Bulgaria
| | - Stoyan K Smoukov
- Queen Mary University of London, School of Engineering and Materials Science, Mile End Road, London E1 4NS, United Kingdom
| | - Radomir I Slavchov
- Queen Mary University of London, School of Engineering and Materials Science, Mile End Road, London E1 4NS, United Kingdom
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Peychev B, Slavchov RI. Interactions between Small Inorganic Ions and Uncharged Monolayers on the Water/Air Interface. J Phys Chem B 2023; 127:2801-2817. [PMID: 36930736 PMCID: PMC10068745 DOI: 10.1021/acs.jpcb.2c08019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2023]
Abstract
The interaction of several simple electrolytes with uncharged insoluble monolayers is studied on the basis of tensiometric and potentiometric data for the surface electrolyte solution|air. The induced adsorption of electrolyte on the monolayer is determined via a combination of data for equilibrium spreading pressure and surface pressure versus area isotherms. We show that the monolayer-induced adsorption of electrolyte is not only strongly ion-specific but also surfactant-specific. The comparison between the ion-specific effects on a carboxylic acid monolayer at low pH and an ester monolayer shows that the anion series follows the same order while the cation series reverses. The effect of the electrolyte on the chemical potential of the monolayer shows attraction between the surfactant and the ions at low monolayer densities, but at high surface densities, repulsion seems to come into play. In nearly all investigated cases, a maximum of monolayer-induced electrolyte adsorption is observed at intermediate monolayer densities. This suggests specific interactions between the surfactant headgroup and the ions. The Volta potential data for the monolayers are analyzed on the basis of the equations of quadrupolar electrostatics. The analysis suggests that the ion-specific effect on the Volta potential is due to the ion-specific decrement of the bulk dielectric constant of the electrolyte solution. Moreover, we present evidence that in most cases the effect of the electrolyte on the orientation of the adsorbed dipoles cannot be neglected. Instead, the change in the ion distribution in the electric double layer seems to have a small effect on the Volta potential.
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Affiliation(s)
- Boyan Peychev
- Queen Mary University of London, School of Engineering and Materials Science, Mile End Road, London E1 4NS, United Kingdom
| | - Radomir I Slavchov
- Queen Mary University of London, School of Engineering and Materials Science, Mile End Road, London E1 4NS, United Kingdom
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Melander MM, Kuisma MJ, Christensen TEK, Honkala K. Grand-canonical approach to density functional theory of electrocatalytic systems: Thermodynamics of solid-liquid interfaces at constant ion and electrode potentials. J Chem Phys 2019; 150:041706. [PMID: 30709274 DOI: 10.1063/1.5047829] [Citation(s) in RCA: 77] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Properties of solid-liquid interfaces are of immense importance for electrocatalytic and electrochemical systems, but modeling such interfaces at the atomic level presents a serious challenge and approaches beyond standard methodologies are needed. An atomistic computational scheme needs to treat at least part of the system quantum mechanically to describe adsorption and reactions, while the entire system is in thermal equilibrium. The experimentally relevant macroscopic control variables are temperature, electrode potential, and the choice of the solvent and ions, and these need to be explicitly included in the computational model as well; this calls for a thermodynamic ensemble with fixed ion and electrode potentials. In this work, a general framework within density functional theory (DFT) with fixed electron and ion chemical potentials in the grand canonical (GC) ensemble is established for modeling electrocatalytic and electrochemical interfaces. Starting from a fully quantum mechanical description of multi-component GC-DFT for nuclei and electrons, a systematic coarse-graining is employed to establish various computational schemes including (i) the combination of classical and electronic DFTs within the GC ensemble and (ii) on the simplest level a chemically and physically sound way to obtain various (modified) Poisson-Boltzmann (mPB) implicit solvent models. The detailed and rigorous derivation clearly establishes which approximations are needed for coarse-graining as well as highlights which details and interactions are omitted in vein of computational feasibility. The transparent approximations also allow removing some of the constraints and coarse-graining if needed. We implement various mPB models within a linear dielectric continuum in the GPAW code and test their capabilities to model capacitance of electrochemical interfaces as well as study different approaches for modeling partly periodic charged systems. Our rigorous and well-defined DFT coarse-graining scheme to continuum electrolytes highlights the inadequacy of current linear dielectric models for treating properties of the electrochemical interface.
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Affiliation(s)
- Marko M Melander
- Nanoscience Center, Department of Chemistry, University of Jyväskylä, P.O. Box 35 (YN), FI-40014 Jyväskylä, Finland
| | - Mikael J Kuisma
- Nanoscience Center, Department of Chemistry, University of Jyväskylä, P.O. Box 35 (YN), FI-40014 Jyväskylä, Finland
| | | | - Karoliina Honkala
- Nanoscience Center, Department of Chemistry, University of Jyväskylä, P.O. Box 35 (YN), FI-40014 Jyväskylä, Finland
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Sun P, Huang K, Liu H. Competitive Adsorption of Ions at the Oil-Water Interface: A Possible Mechanism Underlying the Separation Selectivity for Liquid-Liquid Solvent Extraction. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:13155-13161. [PMID: 30346781 DOI: 10.1021/acs.langmuir.8b02691] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Adsorption, especially competitive adsorption of ions at the interfaces, governs a wealth of physicochemical processes. Understanding the mechanism behind these interfacial behaviors is crucial for developing novel strategies to intensify reactions or transfer processes. Herein, as an example, we found that in the case of liquid-liquid transport of V(V) and Cr(VI) ions, the competitive adsorption of V(V) and Cr(VI) ions against coexisting SO42- ions at the oil-water interface exhibits a significant impact on the selective separation behaviors of V(V) and Cr(VI) ions. The transport of Cr(VI) ions would be hindered by adding Na2SO4 into the aqueous solutions because of the competitive adsorption of SO42- ions at the interface being stronger than that of Cr(VI) ions, whereas the transport of V(V) ions would not be affected because of the stronger affinity of V(V) ions to the interfaces compared to that of SO42- ions. The present work provides new inspirations for developing efficient strategies to improve the separation efficiency of target ions with similar physic-chemical properties by regulating their adsorption behaviors at the interface. It is beneficial to get a deeper understanding into the microscopic nature of competitive adsorption behaviors of ions at interfaces from the interface-molecular level.
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Affiliation(s)
- Pan Sun
- CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering , Chinese Academy of Sciences , Beijing 100190 , P. R. China
- University of Chinese Academy of Sciences , Beijing 100049 , P. R. China
| | - Kun Huang
- CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering , Chinese Academy of Sciences , Beijing 100190 , P. R. China
- School of Metallurgical and Ecological Engineering , University of Science and Technology Beijing , Beijing 100083 , P. R. China
| | - Huizhou Liu
- CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering , Chinese Academy of Sciences , Beijing 100190 , P. R. China
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Duignan TT, Baer MD, Schenter GK, Mundy CJ. Real single ion solvation free energies with quantum mechanical simulation. Chem Sci 2017; 8:6131-6140. [PMID: 28989643 PMCID: PMC5625628 DOI: 10.1039/c7sc02138k] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Accepted: 05/26/2017] [Indexed: 01/11/2023] Open
Abstract
Single ion solvation free energies are one of the most important properties of electrolyte solutions and yet there is ongoing debate about what these values are. Only the values for neutral ion pairs are known. Here, we use DFT interaction potentials with molecular dynamics simulation (DFT-MD) combined with a modified version of the quasi-chemical theory (QCT) to calculate these energies for the lithium and fluoride ions. A method to correct for the error in the DFT functional is developed and very good agreement with the experimental value for the lithium fluoride pair is obtained. Moreover, this method partitions the energies into physically intuitive terms such as surface potential, cavity and charging energies which are amenable to descriptions with reduced models. Our research suggests that lithium's solvation free energy is dominated by the free energetics of a charged hard sphere, whereas fluoride exhibits significant quantum mechanical behavior that cannot be simply described with a reduced model.
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Affiliation(s)
- Timothy T Duignan
- Physical Science Division , Pacific Northwest National Laboratory , P.O. Box 999 , Richland , Washington 99352 , USA . ; Tel: +1 509 3756940
| | - Marcel D Baer
- Physical Science Division , Pacific Northwest National Laboratory , P.O. Box 999 , Richland , Washington 99352 , USA . ; Tel: +1 509 3756940
| | - Gregory K Schenter
- Physical Science Division , Pacific Northwest National Laboratory , P.O. Box 999 , Richland , Washington 99352 , USA . ; Tel: +1 509 3756940
| | - Christopher J Mundy
- Physical Science Division , Pacific Northwest National Laboratory , P.O. Box 999 , Richland , Washington 99352 , USA . ; Tel: +1 509 3756940
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Peshkova TV, Minkov IL, Tsekov R, Slavchov RI. Adsorption of Ions at Uncharged Insoluble Monolayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:8858-8871. [PMID: 27529571 DOI: 10.1021/acs.langmuir.6b02349] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A method is proposed for the experimental determination of the adsorption of inorganic electrolytes at a surface covered with insoluble surfactant monolayer. This task is complicated by the fact that the change of the salt concentration alters both chemical potentials of the electrolyte and the surfactant. Our method resolves the question by combining data for the surface pressure versus area of the monolayer at several salt concentrations with data for the equilibrium spreading pressure of crystals of the surfactant (used to fix a standard state). We applied the method to alcohols spread at the surface of concentrated halide solutions. The measured salt adsorption is positive and has nonmonotonic dependence on the area per surfactant molecule. For the liquid expanded film, depending on the concentration, there is one couple of ions adsorbed per each 3-30 surfactant molecules. We analyzed which ion, the positive or the negative, stands closer to the surface, by measuring the effect of NaCl on the Volta potential of the monolayer. The potentiometric data suggest that Na(+) is specifically adsorbed, while Cl(-) remains in the diffuse layer, i.e., the surface is positively charged. The observed reverse Hofmeister series of the adsorptions of NaF, NaCl, and NaBr suggests the same conclusion holds for all these salts. The force that causes the adsorption of Na(+) seems to be the interaction of the ion with the dipole moment of the monolayer.
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Affiliation(s)
- Tatyana V Peshkova
- Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, Sofia University , 1 J. Bourchier Boulevard, 1164 Sofia, Bulgaria
| | - Ivan L Minkov
- Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, Sofia University , 1 J. Bourchier Boulevard, 1164 Sofia, Bulgaria
- Department of Chemistry, Biochemistry, Physiology, and Pathophysiology, Faculty of Medicine, Sofia University , 1 Koziak Street, 1407 Sofia, Bulgaria
| | - Roumen Tsekov
- Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, Sofia University , 1 J. Bourchier Boulevard, 1164 Sofia, Bulgaria
| | - Radomir I Slavchov
- Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, Sofia University , 1 J. Bourchier Boulevard, 1164 Sofia, Bulgaria
- Department of Chemical Engineering and Biotechnology, Cambridge University , Pembroke Street, New Museums Site, CB2 3RA Cambridge, United Kingdom
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Marcus Y. Specific ion effects on the surface tension and surface potential of aqueous electrolytes. Curr Opin Colloid Interface Sci 2016. [DOI: 10.1016/j.cocis.2016.06.016] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Slavchov RI, Dimitrova IM, Ivanov T. The polarized interface between quadrupolar insulators: Maxwell stress tensor, surface tension, and potential. J Chem Phys 2015; 143:154707. [DOI: 10.1063/1.4933370] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
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10
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Duignan TT, Parsons DF, Ninham BW. Hydronium and hydroxide at the air–water interface with a continuum solvent model. Chem Phys Lett 2015. [DOI: 10.1016/j.cplett.2015.06.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Slavchov RI, Nomura T, Martinac B, Sokabe M, Sachs F. Gigaseal mechanics: creep of the gigaseal under the action of pressure, adhesion, and voltage. J Phys Chem B 2014; 118:12660-72. [PMID: 25295693 PMCID: PMC4226309 DOI: 10.1021/jp506965v] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2014] [Revised: 10/06/2014] [Indexed: 11/28/2022]
Abstract
Patch clamping depends on a tight seal between the cell membrane and the glass of the pipet. Why does the seal have such high electric resistance? Why does the patch adhere so strongly to the glass? Even under the action of strong hydrostatic, adhesion, and electrical forces, it creeps at a very low velocity. To explore possible explanations, we examined two physical models for the structure of the seal zone and the adhesion forces and two respective mechanisms of patch creep and electric conductivity. There is saline between the membrane and glass in the seal, and the flow of this solution under hydrostatic pressure or electroosmosis should drag a patch. There is a second possibility: the lipid core of the membrane is liquid and should be able to flow, with the inner monolayer slipping over the outer one. Both mechanisms predict the creep velocity as a function of the properties of the seal and the membrane, the pipet geometry, and the driving force. These model predictions are compared with experimental data for azolectin liposomes with added cholesterol or proteins. It turns out that to obtain experimentally observed creep velocities, a simple viscous flow in the seal zone requires ~10 Pa·s viscosity; it is unclear what structure might provide that because that viscosity alone severely constrains the electric resistance of the gigaseal. Possibly, it is the fluid bilayer that allows the motion. The two models provide an estimate of the adhesion energy of the membrane to the glass and membrane's electric characteristics through the comparison between the velocities of pressure-, adhesion-, and voltage-driven creep.
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Affiliation(s)
- Radomir I Slavchov
- Sofia University , Department of Physical Chemistry, 1 J. Bourchier Blvd., Sofia 1164, Bulgaria
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Slavchov RI, Peshkova TV. Adsorption of ions at the interface oil|aqueous electrolyte and at interfaces with adsorbed alcohol. J Colloid Interface Sci 2014; 428:257-66. [PMID: 24910061 DOI: 10.1016/j.jcis.2014.04.063] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Revised: 04/26/2014] [Accepted: 04/28/2014] [Indexed: 10/25/2022]
Abstract
We investigate the applicability of the Schmutzer's model for three types of interfaces: aqueous electrolyte|alkane, aqueous electrolyte|long chained alcohol phase, and aqueous electrolyte|alkane with adsorbed alcohol. The model predicts a strong decrease of the electrolyte desorption at water|alcohol interface in comparison with water|alkane, in quantitative agreement with the tensiometric data. The effect is related to the penetration of the alcohol -OH group into the surface layer of the aqueous solution. The same model predicts a decrease with the electrolyte concentration of the chemical potential of the alcohol molecules adsorbed at the water|oil interface, which results in an increase of the adsorption activity of oil-soluble alcohols, again in quantitative agreement with the experiment. The analysis of the deviations of Schmutzer's model predictions from the experimental data for large polarizable anions allows making qualitative conclusions for the magnitude of the ion-specific hydrophobic and dispersion forces at water|gas and water|oil interfaces.
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Comment on "Surface tension of concentrated electrolyte solutions" (R.I. Slavchov, J.K. Novev, J. Colloid Interface Sci. 387 (2012) 234). J Colloid Interface Sci 2014; 423:168-9. [PMID: 24388449 DOI: 10.1016/j.jcis.2013.11.058] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Revised: 11/14/2013] [Accepted: 11/19/2013] [Indexed: 11/22/2022]
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Kazakov DA, Vol’khin VV, Borovkova IS, Popova NP. Kinetics of oxygen absorption by aqueous electrolyte solutions in the presence of microencapsulated quartz particles activating the mass transfer in the liquid phase. RUSS J APPL CHEM+ 2014. [DOI: 10.1134/s1070427214010133] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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