Statistical Mechanics of Multilayer Sorption: Surface Concentration Modeling and XPS Measurement

Toribio, Anthony R.; Prisle, Nønne L.; Wexler, Anthony S.

doi:10.1021/acs.jpclett.8b00332

Cited by 7 publications

(11 citation statements)

References 23 publications

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“…Werner et al (, ) recently studied surfaces of aqueous SCA with and without added salts, using synchrotron radiation‐based XPS in combination with molecular dynamics simulations. Experiments were made with the same setup as used by Walz et al (, ), and direct comparison between experimental and modeled results and our monolayer model is affected by the same issues as pointed out by Toribio et al () for water‐alcohol mixtures. Nevertheless, surface enrichment factors for SCA,

x_{SCA}^{s} false/ x_{SCA}^{b}

, predicted here from the monolayer model are close to the lower range of the corresponding

C_{SCA}^{s} false/ C_{SCA}^{b}

values reported by Werner et al (, ).…”

Section: Resultssupporting

confidence: 90%

“…This was recently highlighted by Toribio et al (), together with other potential challenges to obtaining quantitative surface concentrations from XPS measurements on a 20‐μm liquid microjet (Walz et al, , ). Toribio et al () reported surface enrichment factors for aqueous n ‐butanol, modeled from a statistical mechanics based surface model (Boyer et al, ; Wexler & Dutcher, ), which are of similar magnitude albeit somewhat smaller, compared to the present monolayer model. Curiously, Toribio et al () find similar discrepancies of about a factor of 3 between their model predictions and experimental XPS‐derived surface concentrations of aqueous alcohols (Walz et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…Toribio et al () reported surface enrichment factors for aqueous n ‐butanol, modeled from a statistical mechanics based surface model (Boyer et al, ; Wexler & Dutcher, ), which are of similar magnitude albeit somewhat smaller, compared to the present monolayer model. Curiously, Toribio et al () find similar discrepancies of about a factor of 3 between their model predictions and experimental XPS‐derived surface concentrations of aqueous alcohols (Walz et al, ). This comparison was however done for n ‐butanol concentrations an order of magnitude higher than in the studies compared in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…Thus, the actual observable is the product of the surface concentration-or, in case of neutron reflection experiments, the surface concentration dependent scattering length density-and the probed surface volume, which for planar surfaces is proportional to the surface thickness. This was recently highlighted by Toribio et al (2018), together with other potential challenges to obtaining quantitative surface concentrations from XPS measurements on a 20-μm liquid microjet . Toribio et al (2018) reported surface enrichment factors for aqueous n-butanol, modeled from a statistical mechanics based surface model (Boyer et al, 2015;Wexler & Dutcher, 2013), which are of similar magnitude albeit somewhat smaller, compared to the present monolayer model.…”

Section: Figurementioning

confidence: 99%

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A Monolayer Partitioning Scheme for Droplets of Surfactant Solutions

Malila

Prisle

2018

J Adv Model Earth Syst

120

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Bulk‐surface partitioning of surface active species affects both cloud droplet activation by aerosol particles and heterogeneous atmospheric chemistry. Various approaches are given in the literature to capture this effect in atmospheric models. Here we present a simple, yet physically self‐contained, monolayer model for prediction of both composition and thickness of the surface layer of an aqueous droplet. The monolayer surface model is based on assuming a finite surface layer and mass balance of all species within the droplet. Model predictions are presented for binary and ternary aqueous surfactant model systems and compared to both experimental and model data from the literature and predictions using a common Gibbsian model approach. Deviations from Gibbsian surface thermodynamics due to volume constraints imposed by the finite monolayer lead to stronger predicted surface tension reduction at smaller droplet sizes with the monolayer model. Process dynamics of the presented monolayer model are also contrasted to other recently proposed approaches to treating surface partitioning in droplets, with different underlying assumptions.

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x_{SCA}^{s} false/ x_{SCA}^{b}

, predicted here from the monolayer model are close to the lower range of the corresponding

C_{SCA}^{s} false/ C_{SCA}^{b}

values reported by Werner et al (, ).…”

Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Figurementioning

confidence: 99%

See 2 more Smart Citations

A Monolayer Partitioning Scheme for Droplets of Surfactant Solutions

Malila

Prisle

2018

J Adv Model Earth Syst

120

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“…For the C 1s to O 1s signal intensity ratio, we note that, on the basis of the calibration factor obtained from fitting the TBA concentration dependent data ( Figure 4 ), we can use the TBA-Br solution with its known surface excess to derive the TBA surface excess of the other solutions, as C 1s signal intensity ratios scale linearly with the surface excess for different solutions. 33 , 52 , 54 …”

Section: Resultsmentioning

confidence: 99%

Impact of Tetrabutylammonium on the Oxidation of Bromide by Ozone

Chen

Artiglia

Orlando

et al. 2021

ACS Earth Space Chem.

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The reaction of ozone with sea-salt derived bromide is relevant for marine boundary layer atmospheric chemistry. The oxidation of bromide by ozone is enhanced at aqueous interfaces. Ocean surface water and sea spray aerosol are enriched in organic compounds, which may also have a significant effect on this reaction at the interface. Here, we assess the surface propensity of cationic tetrabutylammonium at the aqueous liquid–vapor interface by liquid microjet X-ray photoelectron spectroscopy (XPS) and the effect of this surfactant on ozone uptake to aqueous bromide solutions. The results clearly indicate that the positively charged nitrogen group in tetrabutylammonium (TBA), along with its surface activity, leads to an enhanced interfacial concentration of both bromide and the bromide ozonide reaction intermediate. In parallel, off-line kinetic experiments for the same system demonstrate a strongly enhanced ozone loss rate in the presence of TBA, which is attributed to an enhanced surface reaction rate. We used liquid jet XPS to obtain detailed chemical composition information from the aqueous-solution–vapor interface of mixed aqueous solutions containing bromide or bromide and chloride with and without TBA surfactant. Core level spectra of Br 3d, C 1s, Cl 2p, N 1s, and O 1s were used for this comparison. A model was developed to account for the attenuation of photoelectrons by the carbon-rich layer established by the TBA surfactant. We observed that the interfacial density of bromide is increased by an order of magnitude in solutions with TBA. The salting-out of TBA in the presence of 0.55 M sodium chloride is apparent. The increased interfacial bromide density can be rationalized by the association constants for bromide and chloride to form ion-pairs with TBA. Still, the interfacial reactivity is not increasing simply proportionally with the increasing interfacial bromide concentration in response to the presence of TBA. The steady state concentration of the bromide ozonide intermediate increases by a smaller degree, and the lifetime of the intermediate is 1 order of magnitude longer in the presence of TBA. Thus, the influence of cationic surfactants on the reactivity of bromide depends on the details of the complex environment at the interface.

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Surfaces of Atmospheric Droplet Models Probed with Synchrotron XPS on a Liquid Microjet

Prisle

2023

Acc. Chem. Res.

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Metrics & MoreArticle Recommendations CONSPECTUS:The atmosphere is a key part of the earth system comprising myriad chemical species in all basic forms of matter.Ubiquitous nano-and microscopic aerosol particles and cloud droplets suspended in the air play crucial roles in earth's climate and the formation of air pollution. Surfaces are a prominent part of aerosols and droplets, due to the high surface area to bulk volume ratios, but very little is known about their specific properties. Many atmospheric compounds are surface-active, leading to enhanced surface concentrations in aqueous solutions. Their distribution between the surface and bulk may determine heterogeneous chemistry and many other properties of aerosol and cloud droplets, but has not been directly observed.We used X-ray photoelectron spectroscopy (XPS) to obtain direct molecular-level information on the surface composition and structure of aqueous solutions of surface-active organics as model systems for atmospheric aerosol and cloud droplets. XPS is a vacuum-based technique enabled for volatile aqueous organic samples by the application of a high-speed liquid microjet. In combination with brilliant synchrotron X-rays, the chemical specificity of XPS allows distinction between elements in different chemical states and positions within molecular structures. We used core-level C 1s and N 1s signals to identify the alkyl and hydrophilic groups of atmospheric carboxylic acids, alkyl-amines, and their conjugate acids and bases. From this, we infer changes in the orientation of surface-adsorbed species and quantify their relative abundances in the surface. XPS-derived surface enrichments of the organics follow trends expected from their surface activities and we observed a preferential orientation at the surface with the hydrophobic alkyl chains pointing increasingly outward from the solution at higher concentrations. This provides a first direct experimental observation of well-established concepts of surface adsorption and confirms the soundness of the method. We mapped relative abundances of conjugate acid−base pairs in the aqueous solution surfaces from the respective intensities of distinctive XPS signals. For each pair, the protonation equilibrium was significantly shifted toward the neutral form in the surface, compared to the bulk solution, across the full pH range. This represents an apparent shift of the pK a in the surface, which may be toward either higher or lower pH, depending on whether the acid or base form of the pair is the neutral species. The surface shifts are broadly consistent with the relative differences in surface enrichment of the individual acid and base conjugates in binary aqueous solutions, with additional contributions from nonideal interactions in the surface. In aqueous mixtures of surface-active carboxylate anions with ammonium salts at near-neutral pH, we found that the conjugate carboxylic acids were further strongly enhanced. This occurs as the coadsorption of weakly basic carboxylate anions and weakly acidic ammoniu...

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Statistical Mechanics of Multilayer Sorption: Surface Concentration Modeling and XPS Measurement

Cited by 7 publications

References 23 publications

A Monolayer Partitioning Scheme for Droplets of Surfactant Solutions

A Monolayer Partitioning Scheme for Droplets of Surfactant Solutions

Impact of Tetrabutylammonium on the Oxidation of Bromide by Ozone

Surfaces of Atmospheric Droplet Models Probed with Synchrotron XPS on a Liquid Microjet

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