Ions at the Water–oil Interface: Interfacial Tension of Electrolyte Solutions

Santos, Alexandre Pereira dos; Levin, Yan

doi:10.1021/la204036e

Cited by 85 publications

(130 citation statements)

References 43 publications

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“…It was soon realized, however, that although the dispersion forces are important for the interaction of ions with the hydrophobic surfaces, they can not explain the propensity of large halogen anions for the air-water interface -the dispersion interactions favor the adsorption of small weakly polarizable cations and not of strongly polarizable anions 61 . Recently, a new theory was developed which allows us to calculate the surface tensions for different electrolytes at various hydrophobic interfaces 20,21,[62][63][64] . The results of the theory are in excellent agreement with the experiments.…”

Section: Hydrophobic Interfacesmentioning

confidence: 99%

Ions at hydrophobic interfaces

Levin

Santos

2014

J. Phys.: Condens. Matter

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We review the present understanding of the behavior of ions at the air-water and oil-water interfaces. We argue that while the alkali metal cations remain strongly hydrated and are repelled from the hydrophobic surfaces, the anions must be classified into kosmotropes and chaotropes. The kosmotropes remain strongly hydrated in the vicinity of a hydrophobic surface, while the chaotropes loose their hydration shell and can become adsorbed to the interface. The mechanism of adsorption is still a subject of debate. Here, we argue that there are two driving forces for anionic adsorption: the hydrophobic cavitational energy and the interfacial electrostatic surface potential of water. While the cavitational contribution to ionic adsorption is now well accepted, the role of the electrostatic surface potential is much less clear. The difficulty is that even the sign of this potential is a subject of debate, with the ab initio and the classical force fields simulations predicting electrostatic surface potentials of opposite sign. In this paper, we will argue that the strong anionic adsorption found in the polarizable force field simulations is the result of the artificial electrostatic surface potential present in the classical water models. We will show that if the adsorption of anions would be as large as predicted by the polarizable force field simulations, the excess surface tension of NaI solution would be strongly negative, contrary to the experimental measurements. While the large polarizability of heavy halides is a fundamental property and must be included in realistic modeling of the electrolytes solutions, we argue that the point charge water models, studied so far, are incompatible with the polarizable ionic force fields when the translational symmetry is broken. The goal for the future should be the development of water models with very low electrostatic surface potential. We believe that such water models will be compatible with the polarizable force fields and can then be used to study the interaction of ions with hydrophobic surfaces and proteins.

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Section: Hydrophobic Interfacesmentioning

confidence: 99%

Ions at hydrophobic interfaces

Levin

Santos

2014

J. Phys.: Condens. Matter

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“…[5][6][7][8][9] Ion polarizability also plays an important role in interfacial phenomena involving aqueous ionic solutions. For example, it affects the interfacial adsorption of ions, 4,10,11 and thus the interfacial tension. 12,13 at water/air or water/oil interfaces.…”

Section: Introductionmentioning

confidence: 99%

Accurate Determination of Ion Polarizabilities in Aqueous Solutions

Zhuang

et al. 2017

J. Phys. Chem. B

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We present a novel method for obtaining salt polarizabilities in aqueous solutions based on our recent theory for the refractive index of salt solutions, which predicts a linear relationship between the refractive index and the salt concentration at low concentrations, with a slope determined by the intrinsic values of the salt polarizability and the density of the solution. Here we apply this theory to determine the polarizabilities of 32 strong electrolyte salts in aqueous solutions from refractive index and density measurements. Setting Li + as the standard ion, we then determine the polarizabilities of seven cations (Na + , K + , Rb + , Cs + , Ca 2+ , Ba 2+ and Sr 2+ ) and seven anions (F − , Cl − , Br − , I − , ClO − 4 , NO − 3 and SO − 4 ), which can be used as important reference data.We investigate the effect of temperature on salt polarizabilities, which decreases slightly with increasing temperature. The ion polarizability is found to be proportional to the cube of bare ionic radius (r 3 bare ) for univalent ions, but the relationship does not hold for multivalent ions. Contrary to findings of Krishnamurti, we find no significant linear relationship between ion polarizability and the square of the atomic number (N 2 ) for smaller ions.

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“…Unfortunately, the state of the art force fields for atomistic simulations lead to too much adsorption of chaotropic ions, resulting in surface tensions which deviate strongly from the experimental measurements [17,35]. On the other hand, the effective potentials used in the present work result in a smaller adsorption and produce surface and interfacial tensions in excellent agreement with the experimental measurements [13,14,16]. This makes it difficult for us to compare our methodology with the classical atomistic simulations.…”

Section: Discussionmentioning

confidence: 78%

“…Following the pioneering work of Hofmeister, the same series has been observed in many other areas of science, ranging from electrochemistry, colloidal science [5,6], surfactant micellization [7], bacterial growth [8], surface and interfacial tensions [9,10], peptide bonds [11], microemulsions [12], etc. Recently, a theory was proposed that allows one to quantitatively predict the effect of Hofmeister ions on the surface [13][14][15] and the interfacial tensions [16,17] of electrolyte and acid solutions. In this paper we want to explore the effect that Hofmeister ions have on the interaction between cationic polyelectrolytes and a hydrophobic surface.…”

Section: Introductionmentioning

confidence: 99%

Adsorption of cationic polyions onto a hydrophobic surface in the presence of Hofmeister salts

Santos

Levin

2013

Soft Matter

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We study, using extensive Monte Carlos simulations, the behavior of cationic polyelectrolytes near hydrophobic surfaces in solutions containing Hofmeister salts. The Hofmeister anions are divided into kosmotropes and chaotropes. Near a hydrophobic surface, the chaotropes lose their solvation sheath and become partially adsorbed to the interface, while the kosmotropes remain strongly hydrated and are repelled from the interface. If the polyelectrolyte solution contains chaotropic anions, a significant adsorption of polyions to the surface is also observed. On the other hand, the kosmotropic anions have only a small influence on the polyion adsorption. These findings can have important implications for exploring the antibacterial properties of cationic polyelectrolytes.

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Ions at the Water–oil Interface: Interfacial Tension of Electrolyte Solutions

Cited by 85 publications

References 43 publications

Ions at hydrophobic interfaces

Ions at hydrophobic interfaces

Accurate Determination of Ion Polarizabilities in Aqueous Solutions

Adsorption of cationic polyions onto a hydrophobic surface in the presence of Hofmeister salts

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