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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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2
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Burrows SA, Shon JW, Peychev B, Slavchov RI, Smoukov SK. Phase transitions of fluorotelomer alcohols at the water|alkane interface studied via molecular dynamics simulation. SOFT MATTER 2024; 20:2243-2257. [PMID: 38351894 DOI: 10.1039/d3sm01444d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/07/2024]
Abstract
Fluorosurfactants are long-lasting environmental pollutants that accumulate at interfaces ranging from aerosol droplet surfaces to cell membranes. Modeling of adsorption-based removal technologies for fluorosurfactants requires accurate simulation methods which can predict their adsorption isotherm and monolayer structure. Fluorotelomer alcohols with one or two methylene groups adjacent to the alcohol (7 : 1 FTOH and 6 : 2 FTOH, respectively) are investigated using the OPLS-AA force field at the water|hexane interface, varying the interfacial area per surfactant. The acquired interfacial pressure isotherms and monolayer phase behavior are compared with previous experimental results. The results are consistent with the experimental data inasmuch as, at realistic adsorption densities, only 7 : 1 FTOH shows a phase transition between liquid-expanded (LE) and 2D crystalline phases. Structures of the LE and crystalline phases are in good agreement with the sticky disc and Langmuir defective crystal models, respectively, used previously to interpret experimental data. Interfacial pressure of the LE phase agrees well with experiment, and sticky disc interaction parameters indicate no 2D LE-gas transition is present for either molecule. Conformation analysis reveals 7 : 1 FTOH favors conformers where the OH dipole is perpendicular to the molecular backbone, such that the crystalline phase is stabilized when these dipoles align.
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Affiliation(s)
- Stephen A Burrows
- Centre for Sustainable Engineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
| | - Jang Won Shon
- Centre for Sustainable Engineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
| | - Boyan Peychev
- Centre for Sustainable Engineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
| | - Radomir I Slavchov
- Centre for Sustainable Engineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
| | - Stoyan K Smoukov
- Centre for Sustainable Engineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
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3
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Xiao T, Zhou Y, Li B. Energy-Scaled Debye-Hückel Theory for the Electrostatic Solvation Free Energy in Size-Asymmetric Electrolyte Solutions. J Phys Chem B 2024; 128:1029-1039. [PMID: 38235680 DOI: 10.1021/acs.jpcb.3c07233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2024]
Abstract
In this report, an energy-scaled Debye-Hückel theory is developed for fast and accurate evaluation of the electrostatic solvation free energy in size-asymmetric electrolyte solutions. A size-asymmetric electrolyte solution is mapped to a dielectric continuum medium with Debye-Hückel-like response. Based on the scaling relation of the electrostatic energy of a spherical ion in the small and large size limits, a Padé polynomial is used to interpolate the electrostatic energy at finite size. The Padé polynomial is further interpreted as the electrostatic energy of an effective Debye-Hückel mean field model, depicted by a modified Debye parameter and a surface charge density due to the size asymmetry of the solvent ions. This theory can distinguish the electrostatic energies and the electrostatic solvation free energies of solutes with the same size but opposite charges. Application to charged hard and charged soft spheres demonstrates the accuracy of our approach.
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Affiliation(s)
- Tiejun Xiao
- Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Guizhou Synergetic Innovation Center of Scientific Big Data for Advanced Manufacturing Technology, Guizhou Education University, Guiyang 550018, People's Republic of China
| | - Yun Zhou
- Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Guizhou Synergetic Innovation Center of Scientific Big Data for Advanced Manufacturing Technology, Guizhou Education University, Guiyang 550018, People's Republic of China
| | - Bo Li
- Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Guizhou Synergetic Innovation Center of Scientific Big Data for Advanced Manufacturing Technology, Guizhou Education University, Guiyang 550018, People's Republic of China
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4
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Boinovich LB, Emelyanenko AM, Emelyanenko KA. Effect of Water Adsorption on Lubricating Film Stability in Slippery Coatings. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:1633-1645. [PMID: 38170923 DOI: 10.1021/acs.langmuir.3c02524] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
The absorption of water by slippery coatings is a ubiquitous phenomenon that arises due to small but finite water dissolution during the contact of aqueous media with lubricants. In this study, using the concept of surface forces, we have analyzed the influence of trace amounts of water in lubricants on the stability of slippery coatings for both coatings with hydrophilic porous bases, prone to form hydrogen bonds with water, and those with hydrophobic porous bases. To perform such analysis, we have considered for the first time the electrostatic problem of the distribution of the electric potential and electric field strength in stratified films that contain two thin dielectric layers imitating the lubricant and a hydrophobic layer sandwiched between the porous substrate and air or water. Based on the developed approach, the equations for the calculation of the excess free energy and the disjoining pressure, associated with water dissolution in the lubricant film, were derived. An analysis of the excess film energy and the contribution of the image interaction to the disjoining pressure isotherm indicates that the dissolved water can both stabilize and destabilize the oil film, depending on the ratio of the static and dynamic dielectric permittivities of the lubricant and the phases confining the film. The results of calculations and simple experiments carried out here indicate much better water contact stability of silicone films impregnating a hydrophobized porous substrate than films impregnating a hydrophilic porous substrate. The obtained results indicate the preference for using the hydrophobic bases for the fabrication of long-lived slippery coatings characterized by better preservation of slippery functional properties under conditions of lubricant depletion and prolonged contact with water.
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Affiliation(s)
- Ludmila B Boinovich
- A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky prospect 31 bldg. 4, 119071 Moscow, Russia
| | - Alexandre M Emelyanenko
- A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky prospect 31 bldg. 4, 119071 Moscow, Russia
| | - Kirill A Emelyanenko
- A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky prospect 31 bldg. 4, 119071 Moscow, Russia
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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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6
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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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7
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Xiao T, Song X. A Systematic Way to Extend the Debye-Hückel Theory beyond Dilute Electrolyte Solutions. J Phys Chem A 2021; 125:2173-2183. [PMID: 33661015 DOI: 10.1021/acs.jpca.0c10226] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
An extended Debye-Hückel theory with fourth order gradient term is developed for electrolyte solutions; namely, the electric potential φ(r) of the bulk electrolyte solution can be described by ∇2φ(r) = κ2φ(r) + LQ2∇4φ(r), where the parameters κ and LQ are chosen to reproduce the first two roots of the dielectric response function of the bulk solution. Three boundary conditions for solving the electric potential problem are proposed based upon the continuity conditions of involving functions at the dielectric boundary, with which a boundary element method for the electric potential of a solute with a general geometrical shape and charge distribution is derived. Solutions for the electric potential of a spherical ion and a diatomic molecule are found and used to calculate their electrostatic solvation energies. The validity of the theory is successfully demonstrated when applied to binary as well as multicomponent primitive models of electrolyte solutions.
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Affiliation(s)
- Tiejun Xiao
- Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Guizhou Synergetic Innovation Center of Scientific Big Data for Advanced Manufacturing Technology, Guizhou Education University, Guiyang 550018, People's Republic of China
| | - Xueyu Song
- Department of Chemistry and Ames Laboratory, Iowa State University, Ames, Iowa 50011, United States
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8
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Dimitrova IM, Yordanova VI, Slavchov RI. Quadrupolarizability of Liquid Mixtures. J Phys Chem B 2020; 124:11711-11717. [PMID: 33319562 DOI: 10.1021/acs.jpcb.0c08841] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Theoretical expressions for the macroscopic polarizability and quadrupolarizability of a quadrupolar mixture are derived. The theory is demonstrated on the example of a liquid mixture of methane and nitrogen (nonquadrupolar plus quadrupolar component). It turns out that the dielectric permittivity (the "dipole strength" of the liquid) of this mixture changes little with the composition, while the quadrupolar length ("quadrupolar strength") almost triples as the fraction of nitrogen approaches one. A set of such mixtures can be used as standard quadrupolar solvents to study systematically phenomena such as quadrupolar solvatochromism, the effect of the solvent on the rate of a reaction etc.
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Affiliation(s)
- Iglika M Dimitrova
- Department of Physical Chemistry, University of Chemical Technology and Metallurgy, 8 Kliment Ohridski Boulevard, BG-1756 Sofia, Bulgaria.,Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Boulevard, BG-1784 Sofia, Bulgaria
| | - Velislava I Yordanova
- Department of Physical Chemistry, University of Chemical Technology and Metallurgy, 8 Kliment Ohridski Boulevard, BG-1756 Sofia, Bulgaria
| | - Radomir I Slavchov
- School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London, E1 4NS, U.K
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Slavchov RI, Dimitrova IM, Menon A. From the molecular quadrupole moment of oxygen to the macroscopic quadrupolarizability of its liquid phase. J Chem Phys 2019. [DOI: 10.1063/1.5110675] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Radomir I. Slavchov
- School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom
| | - Iglika M. Dimitrova
- Faculty of Chemical Technologies, Department of Physical Chemistry, University of Chemical Technology and Metallurgy, 8, Kliment Ohridski Blvd., BG-1756 Sofia, Bulgaria
| | - Angiras Menon
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridgeshire CB3 0AS, United Kingdom
- Cambridge Centre for Advanced Research and Education in Singapore (CARES), CREATE Tower, 1 Create Way, Singapore 138602
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10
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Doyle CC, Shi Y, Beck TL. The Importance of the Water Molecular Quadrupole for Estimating Interfacial Potential Shifts Acting on Ions Near the Liquid–Vapor Interface. J Phys Chem B 2019; 123:3348-3358. [DOI: 10.1021/acs.jpcb.9b01289] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Carrie C. Doyle
- Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States
| | - Yu Shi
- Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States
| | - Thomas L. Beck
- Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States
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Fiedler J, Parsons DF, Burger FA, Thiyam P, Walter M, Brevik I, Persson C, Buhmann SY, Boström M. Impact of effective polarisability models on the near-field interaction of dissolved greenhouse gases at ice and air interfaces. Phys Chem Chem Phys 2019; 21:21296-21304. [DOI: 10.1039/c9cp03165k] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The microscopic behaviour of neutral and dissolved particles near the boundary interface has been investigated. Depending on the applied excess polarisability model the results change dramatically from attraction to repulsion.
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Affiliation(s)
- Johannes Fiedler
- Physikalisches Institut
- Albert-Ludwigs-Universität Freiburg
- 79104 Freiburg
- Germany
- Centre for Materials Science and Nanotechnology
| | | | | | | | - Michael Walter
- Physikalisches Institut
- Albert-Ludwigs-Universität Freiburg
- 79104 Freiburg
- Germany
- FIT Freiburg Centre for Interactive Materials and Bioinspired Technologies
| | - I. Brevik
- Department of Energy and Process Engineering
- Norwegian University of Science and Technology
- NO-7491 Trondheim
- Norway
| | - Clas Persson
- Centre for Materials Science and Nanotechnology
- Department of Physics
- University of Oslo
- NO-0316 Oslo
- Norway
| | - Stefan Yoshi Buhmann
- Physikalisches Institut
- Albert-Ludwigs-Universität Freiburg
- 79104 Freiburg
- Germany
- Freiburg Institute for Advanced Studies
| | - Mathias Boström
- Centre for Materials Science and Nanotechnology
- Department of Physics
- University of Oslo
- NO-0316 Oslo
- Norway
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Slavchov RI, Ivanov IB. Effective osmotic cohesion due to the solvent molecules in a delocalized adsorbed monolayer. J Colloid Interface Sci 2018; 532:746-757. [DOI: 10.1016/j.jcis.2018.08.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 08/08/2018] [Accepted: 08/09/2018] [Indexed: 10/28/2022]
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Slavchov RI, Dimitrova IM, Radoev BP. Contribution of the surface dipole moment and the contact potential-induced disjoining pressure to the stress balance at a three-phase contact. COLLOID JOURNAL 2017. [DOI: 10.1134/s1061933x17060151] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Dimitrova IM, Slavchov RI, Ivanov T, Mosbach S. Comment on “A spherical cavity model for quadrupolar dielectrics” [J. Chem. Phys. 144, 114502 (2016)]. J Chem Phys 2017. [DOI: 10.1063/1.4979717] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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15
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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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16
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Dimitrova IM, Slavchov RI, Ivanov T, Mosbach S. A spherical cavity model for quadrupolar dielectrics. J Chem Phys 2016; 144:114502. [PMID: 27004882 DOI: 10.1063/1.4943196] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The dielectric properties of a fluid composed of molecules possessing both dipole and quadrupole moments are studied based on a model of the Onsager type (molecule in the centre of a spherical cavity). The dielectric permittivity ε and the macroscopic quadrupole polarizability αQ of the fluid are related to the basic molecular characteristics (molecular dipole, polarizability, quadrupole, quadrupolarizability). The effect of αQ is to increase the reaction field, to bring forth reaction field gradient, to decrease the cavity field, and to bring forth cavity field gradient. The effects from the quadrupole terms are significant in the case of small cavity size in a non-polar liquid. The quadrupoles in the medium are shown to have a small but measurable effect on the dielectric permittivity of several liquids (Ar, Kr, Xe, CH4, N2, CO2, CS2, C6H6, H2O, CH3OH). The theory is used to calculate the macroscopic quadrupolarizabilities of these fluids as functions of pressure and temperature. The cavity radii are also determined for these liquids, and it is shown that they are functions of density only. This extension of Onsager's theory will be important for non-polar solutions (fuel, crude oil, liquid CO2), especially at increased pressures.
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Affiliation(s)
- Iglika M Dimitrova
- Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria
| | - Radomir I Slavchov
- Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria
| | - Tzanko Ivanov
- Department of Theoretical Physics, Faculty of Physics, Sofia University, 1164 Sofia, Bulgaria
| | - Sebastian Mosbach
- Department of Chemical Engineering and Biotechnology, Cambridge University, CB2 3RA Cambridge, United Kingdom
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17
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The impact of nonelectrostatic physisorption of ions on free energies and forces between redox electrodes: ion-specific repulsive peaks. Electrochim Acta 2016. [DOI: 10.1016/j.electacta.2015.12.090] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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