Molecular Dynamics Study of Gas−Liquid Aqueous Sodium Halide Interfaces. I. Flexible and Polarizable Molecular Modeling and Interfacial Properties

Ishiyama, Tatsuya; Morita, Akihiro

doi:10.1021/jp065191s

Cited by 156 publications

(321 citation statements)

References 92 publications

(182 reference statements)

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“…[14][15][16][17][18][19][20][21][22][23][24] The contribution of anion polarizability to interfacial enhancement is evident in the MD simulations where in the absence of the polarizability factor anion enhancement was not observed. [40][41][42] The results presented here for the multi component We see a significant surface enhancement (and subsurface depletion) of bromide, compared to which the surface peak of chloride is strongly suppressed.…”

Section: Resultsmentioning

confidence: 99%

“…Surface segregation of bromide in NaBr/NaCl crystals has previously been reported by our group and others. 14,[23][24][25] The bromide surface segregation reported in these studies can be attributed to the different solubilities of NaBr and NaCl in water, as well as heterogeneous crystal growth resulting in NaBr-rich domains. However, they …”

Section: Discussionmentioning

confidence: 99%

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Ion Partitioning at the Liquid/Vapor Interface of a Multicomponent Alkali Halide Solution: A Model for Aqueous Sea Salt Aerosols

et al. 2008

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The chemistry of Br species associated with sea salt ice and aerosols has been implicated in the episodes of ozone depletion reported at Arctic sunrise. However, Br -is only a minor component in sea salt, which has a Br -/Cl -molar ratio of ~0.0015. Sea salt is a complex mixture of many different species, with NaCl as the primary component. In recent years experimental and theoretical studies have reported enhancement of the large, more polarizable halide ion at the liquid/vapor interface of corresponding aqueous alkali halide solutions. The proposed enhancement is likely to influence the availability of sea salt Br -for heterogeneous reactions such as those involved in the ozone depletion episodes. We report here ambient pressure x-ray photoelectron spectroscopy studies and molecular dynamics simulations showing direct evidence of Br -enhancement at the interface of an aqueous NaCl solution doped with bromide. The experiments were carried out on samples with Br -/Cl -ratios in the range 0.1% to 10%, the latter being also the ratio for which simulations were carried out. This is the first direct measurement of interfacial enhancement of Br -in a multi-component solution with particular relevance to sea salt chemistry.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Ion Partitioning at the Liquid/Vapor Interface of a Multicomponent Alkali Halide Solution: A Model for Aqueous Sea Salt Aerosols

et al. 2008

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“…1 However, a combination of computational [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and experimental studies [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] has shown that ions can reside and even be enhanced at the interface.…”

Section: Introductionmentioning

confidence: 99%

The effect of cations on NO₂ production from the photolysis of aqueous thin water films of nitrate salts

Richards-Henderson

Anderson

Anastasio

et al. 2015

Phys. Chem. Chem. Phys.

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The photochemistry of nitrate ions in bulk aqueous solution is well known, yet recent evidence suggests that the photolysis of nitrate may be more efficient at the air-water interface. Whether and how this surface enhancement is altered by the presence of different cations is not known. In the present studies, thin aqueous films of nitrate salts with different cations were deposited on the walls of a Teflon chamber and irradiated with 311 nm light at 298 K. The films were generated by nebulizing aqueous 0.5 M solutions of the nitrate salts and the generation of gas-phase NO 2 was monitored with time. The nitrate salts fall into three groups based on their observed rate of NO 2 formation (R NO 2 ): (1) RbNO 3 and KNO 3 , which readily produce NO 2 (R NO 2 4 3 ppb min À1 ), (2) Ca(NO 3 ) 2 , which produces NO 2 more slowly (R NO 2 o 1 ppb min À1 ), and (3) Mg(NO 3 ) 2 and NaNO 3 , which lie between the other two groups. Neither differences in the UV-visible spectra of the nitrate salt solutions nor the results of bulk-phase photolysis studies could explain the differences in the rates of NO 2 production between these three groups. These experimental results, combined with some insights from previous molecular dynamic simulations and vibrational sum frequency generation studies, show that cations may impact the concentration of nitrate ions in the interface region, thereby directly impacting the effective quantum yields for nitrate ions.

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“…28 In addition to polymer surfaces, MD has also been used to explain the SFG spectra of interfacial water 29 and aqueous solutions. 30 In this study, we have combined SFG, all-atom MD simulations, and ab initio calculations to resolve the open questions regarding the molecular structure of PMMA surfaces. The results of this work are divided into two papers.…”

Section: ■ Introductionmentioning

confidence: 99%

Molecular Structure of Poly(methyl methacrylate) Surface II: Effect of Stereoregularity Examined through All-Atom Molecular Dynamics

et al. 2014

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The chemical composition and molecular structure of polymeric surfaces are important in understanding wetting, adhesion, and friction. Here, we combine interfacesensitive sum frequency generation spectroscopy (SFG), allatom molecular dynamics (MD) simulations, and ab initio calculations to understand the composition and the orientation of chemical groups on poly(methyl methacrylate) (PMMA) surface as a function of tacticity and temperature. The SFG spectral features for isotactic and syndiotactic PMMA surfaces are similar, and the dominant peak in the spectra corresponds to the ester-methyl groups. The SFG spectra for solid and melt states are very similar for both syndiotactic and isotactic PMMA. In comparison, the MD simulation results show that both the ester-methyl and the α-methyl groups of syndiotactic-PMMA are ordered and tilted toward the surface normal. For the isotactic-PMMA, the α-methyl groups are less ordered compared to their ester-methyl groups. The backbone methylene groups have a broad angular distribution and are disordered, independent of tacticity and temperature. We have compared the SFG results with theoretical spectra calculated using MD simulations and ab initio calculations. Our analysis shows that the weaker intensity of α-methyl groups in SFG spectra is due to a combination of smaller molecular hyperpolarizability, lower ordering, and lower surface number density. This work highlights the importance of combining SFG spectroscopy with MD simulations and ab initio calculations in understanding polymer surfaces. ■ INTRODUCTIONOne of the simplest and still commonly used technique to characterize surfaces of polymers is the measurement of water contact angle. Although this is a very simple technique to judge the wettability of surfaces, it lacks molecular level sensitivity to identify the chemical composition and molecular structure of surfaces. In addition, the rearrangement of molecules at the surface after exposure to water complicates the interpretation of contact angle results. 1 X-ray photoelectron spectroscopy (XPS), a vacuum-based technique, provides excellent information regarding the elemental composition present at the surfaces. However, to identify different hydrocarbon groups (or bondings) is not trivial and relies on subtle shifts of carbon binding energies in the high-resolution XPS analysis. 2 Attenuated-total-reflectance infrared can be used to pick up molecular fingerprints, but this technique samples a much thicker layer than the surface region that affects wetting, surface energy, and friction. 3 In the past two decades, surface-sensitive infrared−visible sum frequency generation spectroscopy (SFG) has been used to study polymer surfaces, 4−7 polymer/liquid interfaces, 7−11 polymer/metal or metal oxide interfaces, 5,12−15 and polymer/polymer interfaces. 12,16−19 SFG is a second-order nonlinear optical technique, and under electric dipole approximation, the SFG signal is only generated by the ordered molecules at surfaces or interfaces and the contribution from ...

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Molecular Dynamics Study of Gas−Liquid Aqueous Sodium Halide Interfaces. I. Flexible and Polarizable Molecular Modeling and Interfacial Properties

Cited by 156 publications

References 92 publications

Ion Partitioning at the Liquid/Vapor Interface of a Multicomponent Alkali Halide Solution: A Model for Aqueous Sea Salt Aerosols

Ion Partitioning at the Liquid/Vapor Interface of a Multicomponent Alkali Halide Solution: A Model for Aqueous Sea Salt Aerosols

The effect of cations on NO₂ production from the photolysis of aqueous thin water films of nitrate salts

Molecular Structure of Poly(methyl methacrylate) Surface II: Effect of Stereoregularity Examined through All-Atom Molecular Dynamics

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Molecular Dynamics Study of Gas−Liquid Aqueous Sodium Halide Interfaces. I. Flexible and Polarizable Molecular Modeling and Interfacial Properties

Cited by 156 publications

References 92 publications

Ion Partitioning at the Liquid/Vapor Interface of a Multicomponent Alkali Halide Solution: A Model for Aqueous Sea Salt Aerosols

Ion Partitioning at the Liquid/Vapor Interface of a Multicomponent Alkali Halide Solution: A Model for Aqueous Sea Salt Aerosols

The effect of cations on NO2 production from the photolysis of aqueous thin water films of nitrate salts

Molecular Structure of Poly(methyl methacrylate) Surface II: Effect of Stereoregularity Examined through All-Atom Molecular Dynamics

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Product

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The effect of cations on NO₂ production from the photolysis of aqueous thin water films of nitrate salts