Ion hydration near air/water interfaces and the structure of liquid surfaces

CONWAY, B

doi:10.1016/s0022-0728(75)80145-8

Cited by 9 publications

(5 citation statements)

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“…The ion is at the center of a hollow sphere of radius r 0 . The electrostatic energy of a monovalent ion, employing a radial field approximation used by Conway, is a volume integral where q e is the electron charge and r⃗ ion is the position of the ion, with | r⃗ − r⃗ ion | ≥ r 0 , the radius of the hydrated ion. This function easily integrates for slabs of the dielectric, even when the hollow sphere overlaps them.…”

Section: Resultsmentioning

confidence: 99%

Ion Transport in Micelle-like Films: Soft-Landed Ion Studies

Iedema

Cowin

2000

Langmuir

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Ion-transport processes across epitaxially grown micelle-like films in the form of liquid hydrocarbon/ water/hydrocarbon sandwiches were studied by a novel ion soft-landing technique. Centered inside of vapor-deposited glassy films of 3-methylpentane (166 monolayers) and methylcyclohexane (50 monolayers) was a water layer from 0 to 10 monolayers thick. From 90 to 150 K we time-resolved hydronium ion motion and found that the ions (D3O + ) clearly paused in the aqueous phase, being transiently trapped by solvation interactions. A modified Born solvation model qualitatively showed that a trap energy gradually built up in the aqueous phase with the water layer thickness.

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Section: Resultsmentioning

confidence: 99%

Ion Transport in Micelle-like Films: Soft-Landed Ion Studies

Iedema

Cowin

2000

Langmuir

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“…The surface tension, or surface free energy per unit area, may be thought of as the work of creating additional liquid surface from the interior solution (5). All of the neutral salts increase the surface tension of the water, indicating a deficiency of solute close to the surface (5,65,148,661). For an o-i M solution of alkali metal chloride this solute-free layer is about 5 A (303, 314, 373~374, 515, 716-717) or about (5 A/276 A) (555) two water molecules.…”

Section: A Molecular Mechanism For the Origins Of H O F M E I S mentioning

confidence: 99%

The Hofmeister effect and the behaviour of water at interfaces

Collins

Washabaugh

1985

Quart. Rev. Biophys.

1,544

1,455

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Starting from known properties of non-specific salt effects on the surface tension at an air-water interface, we propose the first general, detailed qualitative molecular mechanism for the origins of ion-specific (Hofmeister) effects on the surface potential difference at an air-water interface; this mechanism suggests a simple model for the behaviour of water at all interfaces (including water-solute interfaces), regardless of whether the non-aqueous component is neutral or charged, polar or non-polar. Specifically, water near an isolated interface is conceptually divided into three layers, each layer being I water-molecule thick. We propose that the solute determines the behaviour of the adjacent first interfacial water layer (I1); that the bulk solution determines the behaviour of the third interfacial water layer (I3), and that both I1 and I3 compete for hydrogen-bonding interactions with the intervening water layer (I2), which can be thought of as a transition layer. The model requires that a polar kosmotrope (polar water-structure maker) interact with I1 more strongly than would bulk water in its place; that a chaotrope (water-structure breaker) interact with I1 somewhat less strongly than would bulk water in its place; and that a non-polar kosmotrope (non-polar water-structure maker) interact with I1 much less strongly than would bulk water in its place. We introduce two simple new postulates to describe the behaviour of I1 water molecules in aqueous solution. The first, the 'relative competition' postulate, states that an I1 water molecule, in maximizing its free energy (--delta G), will favour those of its highly directional polar (hydrogen-bonding) interactions with its immediate neighbours for which the maximum pairwise enthalpy of interaction (--delta H) is greatest; that is, it will favour the strongest interactions. We describe such behaviour as 'compliant', since an I1 water molecule will continually adjust its position to maximize these strong interactions. Its behaviour towards its remaining immediate neighbours, with whom it interacts relatively weakly (but still favourably), we describe as 'recalcitrant', since it will be unable to adjust its position to maximize simultaneously these interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

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“…We had concluded that 15 ML or thicker water layers made a solvation trap that was 0.4 eV deep and that the dependence of the trap depth on water thickness was very well fit by a Born model, with a Born radius of the ion of 4.6 Å and a water dielectric constant on the order of 100. The Born model had been calculated using an analytical approximation used by Conway . We have since compared his analytical equation against numerical and other analytical calculations and found that the Conway approximation is only accurate for small differences in the dielectric constant at the interface, not the case here.…”

Section: Determining the Solvation Trap Potential Depth And Shapementioning

confidence: 99%

“…Ion transport across the interface between two media was treated in 1920 by Born, who derived a continuum fluid equation describing the energy of an ion in a medium, and numerous improvements to continuum theories have been introduced. , Molecular dynamics approaches have been developed to study liquid−liquid systems . We refer the readers to reviews by Benjamin , and papers by Dang and co-workers. − Theoretical calculations have generated many interesting predictions that in many cases await adequate experimental verification.…”

Section: Introductionmentioning

confidence: 99%

Sculpting the Oil−Water Interface to Probe Ion Solvation

Iedema

Schenter

et al. 2001

J. Phys. Chem. B

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Solvation of ions at oil-water interfaces is so important in cell wall and enzyme function, colloidal chemistry, fuel cells, and other areas that substantial effort has been made to understand the process via molecular-scale simulations of well-specified model systems. Here we report a series of experiments probing ion transport and solvation in composite films that have a geometrical specificity that rivals what theory is routinely able to employ. Proton/hydronium transport across the water-organic interface has been studied using a novel "soft-landed" ion technique that allows precision tailoring of the interfaces (including initial ion position) and sensitive monitoring of the ion motion via the electric potential generated by the ions. There are two main findings. First, the ion solvation by water at the organic-aqueous interface is probed continuously for various monolayers of water present in simple and complex sandwiched structures. The potential trap created by the solvation can be systematically overwhelmed by the collective electric field of the ions, giving us some unique information about both the trap depth and shape. A simple Born model for the trap reproduces some, but not all, of the details experimentally observed. Second, ion transport in several organic glasses is well-predictable by continuum viscosity models at electric fields up to approximately 10 8 V/m.

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Ion hydration near air/water interfaces and the structure of liquid surfaces

Cited by 9 publications

References 0 publications

Ion Transport in Micelle-like Films: Soft-Landed Ion Studies

Ion Transport in Micelle-like Films: Soft-Landed Ion Studies

The Hofmeister effect and the behaviour of water at interfaces

Sculpting the Oil−Water Interface to Probe Ion Solvation

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