Propensity of soft ions for the air/water interface

Vrbka, Luboš; Mucha, Martin; Minofar, Babak; Jungwirth, Pavel; Brown, Eric C.; Tobias, Douglas J.

doi:10.1016/j.cocis.2004.05.028

Cited by 209 publications

(409 citation statements)

References 23 publications

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“…(Fig. 2.) Whereas a fully charged iodide anion in nonpolarizable models of this kind exhibits little or no affinity for the liquid-vapor interface (30), the average concentration of I Ϫ3/4 in the interfacial region rises more than 90-fold over its bulk value. Fully charged cations exhibit still less affinity than nonpolarizable monovalent anions; by contrast, I ϩ3/4 is nearly 5ϫ more concentrated at z Ϸz Gibbs than in bulk.…”

Section: Resultsmentioning

confidence: 99%

“…We plot the average solute concentration relative to its value deep within bulk solution, c(z) ϭ ͳ ion (z)ʹ/ bulk , as a function of solute height z. For the case ( * ion ϭ 1.5, q* ion ϭ Ϯ7), ion density rises at the interface to a value nearly 3ϫ that in bulk, rivaling the largest magnitudes of surface enhancement reported for computer simulations of atomic ions in water (30). As in the case of hydrated halide anions, adsorption can be suppressed entirely by a modest reduction in solute size, as shown for ( * ion ϭ 1.25, q* ion ϭ Ϯ7).…”

Section: Resultsmentioning

confidence: 99%

“…They are dramatically evident for ions held more than a molecular diameter above the Gibbs dividing surface, which extrude a thin column of solvent molecules from the slab. Ions positioned closer to the dividing surface effect more subtle distortions but still noticeably draw nearby solvent molecules farther toward the vapor phase than they would reside on average in the This persistence of electric-field fluctuations can also be viewed as a key reason that ion polarizability tends, as several studies have emphasized (30,37,38), to promote surface enhancement. Although our simulations involve exclusively nonpolarizable ions, we can write the density profiles of their polarizable counterparts exactly in terms of statistical properties of nonpolarizable reference systems:…”

Section: Resultsmentioning

confidence: 99%

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On the fluctuations that drive small ions toward, and away from, interfaces between polar liquids and their vapors

Noah-Vanhoucke

Geissler

2009

Proc. Natl. Acad. Sci. U.S.A.

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Contrary to the expectations from classic theories of ion solvation, spectroscopy and computer simulations of the liquid-vapor interface of aqueous electrolyte solutions suggest that ions little larger than a water molecule can prefer to reside near the liquid's surface. Here we advance the view that such affinity originates in a competition between strong opposing forces, primarily due to volume exclusion and dielectric polarization, that are common to all dense polar liquids. We present evidence for this generic mechanism from computer simulations of (i) water and (ii) a Stockmayer fluid near its triple point. In both cases, we show that strong surface enhancement of small ions, obtained by tuning solutes' size and charge, can be accentuated or suppressed by modest changes in either of those parameters. Statistics of solvent polarization, when the ion is held at and above the Gibbs dividing surface, highlight a basic deficiency in conventional models of dielectric response, namely, the neglect of interfacial flexibility. By distorting the solution's boundary, an ion experiences fluctuations in electrostatic potential and in electric field whose magnitudes attenuate much more gradually (as the ion is removed from the liquid phase) than for a quiescent planar interface. As one consequence, the collective responses that determine free energies of solvation can resolve very differently in nonuniform environments than in bulk. We show that this persistence of electric-field fluctuations additionally shapes the sensitivity of solute distributions to ion polarizability. dielectric continuum ͉ ion solvation ͉ liquid-vapor interface ͉ polarizability ͉ water S imple salts dissolve in water because the electrostatic reaction fields induced by separated ions in solution provide greatly favorable energies, more than sufficient to offset intrinsic costs of dissociation. These substantial solvation energies are captured with remarkable accuracy by simple linear response models for solvent polarization, for instance dielectric continuum theory (DCT) (1). Molecular simulations of bulk solutions further indicate that the presumption of Gaussian-distributed polarization fluctuations underlying these theories is appropriate even on microscopic scales (2). Based on these facts, one might expect small ions (little larger than a water molecule) to avoid interfaces with lower dielectric media, such as vapor, as predicted by straightforward DCT calculations. Surprisingly, a large body of computational work (pioneered by Jungwirth and Tobias) (refs. 3 and 4 and references therein, 5-9) and many experiments (10, ref. 11 and references therein, 12-14) suggest that certain small ions are in fact more concentrated near the liquid-vapor interface than in bulk aqueous solution. This counterintuitive phenomenon not only challenges the textbook understanding of ion solvation in polar liquids but also bears importantly on a wide range of important molecular processes, e.g., formation of sea salt aerosols and subsequent halogen-release mechani...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

On the fluctuations that drive small ions toward, and away from, interfaces between polar liquids and their vapors

Noah-Vanhoucke

Geissler

2009

Proc. Natl. Acad. Sci. U.S.A.

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“…In addition, there are also inorganic sources of iodine. For example, the direct photochemical oxidation if iodide at the sea-air interface (Miyake & Tsunogai 1963) is likely to be an important source as is the oxidation by ozone of seawater iodide, followed by the release of I 2 into the gas phase (Vrbka et al 2004). The latter mechanism depends on ozone deposition at the ocean surface and the production of I 2 must take place at the air-sea interface for volatilization to occur.…”

Section: Secondary Aerosol Formation From Iodine Vapoursmentioning

confidence: 99%

Marine aerosol production: a review of the current knowledge

O’Dowd

Leeuw

2007

Phil. Trans. R. Soc. A.

661

568

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The current knowledge in primary and secondary marine aerosol formation is reviewed. For primary marine aerosol source functions, recent source functions have demonstrated a significant flux of submicrometre particles down to radii of 20 nm. Moreover, the source functions derived from different techniques up to 10 mm have come within a factor of two of each other. For secondary marine aerosol formation, recent advances have identified iodine oxides and isoprene oxidation products, in addition to sulphuric acid, as contributing to formation and growth, although the exact roles remains to be determined. While a multistep process seems to be required, isoprene oxidation products are more likely to participate in growth and sulphuric acid is more likely to participate in nucleation. Iodine oxides are likely to participate in both nucleation and growth.

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“…), i.e., the specific local properties of the liquid were by no means taken into account; here we speak about the dipole moments and polarizabilities of molecules, and their sizes. The subsequent numerous theoretical works allowed for the geometrical characteristics of water molecule [27], numerical MD simulation in the view of the effect of polarization of water molecules [28][29][30][31][32][33][34][35][36][37][38], and also series of experimental results including vibrational sum frequency generation spectroscopy [39][40][41][42][43][44], second harmonic generation spectroscopy [45,46], high-pressure VUV photoelectron spectroscopy [47,48], and X-ray photoelectron spectroscopy combined with scanning electron microscopy [49,50] allow us to make a conclusion about an opportunity of adsorption of some anions, for example, Cl − , I − and Br − on the watergas interface. The fact that basically negative ions are capable of adsorption at this interface is also supported by the data obtained in Ref.…”

Section: Statement Of the Problem Introductionmentioning

confidence: 99%

Structure of the nanobubble clusters of dissolved air in liquid media

et al. 2011

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A qualitative model of the nucleation of stable bubbles in water at room temperature is suggested. This model is completely based on the property of the affinity of water at the nanometer scale; it is shown that under certain conditions the extent of disorder in a liquid starts growing, which results in a spontaneous decrease of the local density of the liquid and in the formation of nanometer-sized voids. These voids can serve as nuclei for the following generation of the so-called bubstons (the abbreviation for bubbles, stabilized by ions). The model of charging the bubstons by the ions, which are capable of adsorption, and the screening by a cloud of counter-ions, which are incapable of adsorption, is analyzed. It was shown that, subject to the charge of bubston, two regimes of such screening can be realized. At low charge of bubston the screening is described in the framework of the known linearized Debye-Huckel approach, when the sign of the counterion cloud preserves its sign everywhere in the liquid surrounding the bubston, whereas at large charge this sign is changed at some distance from the bubston surface. This effect provides the mechanism of the emergence of two types of compound particles having the opposite polarity, which leads to the aggregation of such compound particles by a ballistic kinetics.

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Propensity of soft ions for the air/water interface

Cited by 209 publications

References 23 publications

On the fluctuations that drive small ions toward, and away from, interfaces between polar liquids and their vapors

On the fluctuations that drive small ions toward, and away from, interfaces between polar liquids and their vapors

Marine aerosol production: a review of the current knowledge

Structure of the nanobubble clusters of dissolved air in liquid media

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