Elucidating the mechanism of selective ion adsorption to the liquid water surface
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TLDR
Negative adsorption enthalpies thus reflect a simple repartitioning of solvent density among surface, bulk, and coordination regions, and a different, and much less spatially local, mechanism underlies the concomitant loss of entropy.Abstract:
Adsorption of aqueous thiocyanate ions from bulk solution to the liquid/vapor interface was measured as a function of temperature by resonant UV second harmonic generation spectroscopy. The resulting adsorption enthalpy and entropy changes of this prototypical chaotrope were both determined to be negative. This surprising result is supported by molecular simulations, which clarify the microscopic origins of observed thermodynamic changes. Calculations reveal energetic influences of adsorbed ions on their surroundings to be remarkably local. Negative adsorption enthalpies thus reflect a simple repartitioning of solvent density among surface, bulk, and coordination regions. A different, and much less spatially local, mechanism underlies the concomitant loss of entropy. Simulations indicate that ions at the interface can significantly bias surface height fluctuations even several molecular diameters away, imposing restrictions consistent with the scale of measured and computed adsorption entropies. Based on these results, we expect an ion’s position in the Hofmeister lyotropic series to be determined by a combination of driving forces associated with the pinning of capillary waves and with a competition between ion hydration energy and the neat liquid’s surface tension.read more
Citations
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Water at Interfaces
Olle Björneholm,Martin Hangaard Hansen,Martin Hangaard Hansen,Andrew Hodgson,Li-Min Liu,David T. Limmer,Angelos Michaelides,Philipp Pedevilla,Jan Rossmeisl,Huaze Shen,Gabriele Tocci,Gabriele Tocci,Eric Tyrode,Marie-Madeleine Walz,Josephina Werner,Josephina Werner,Hendrik Bluhm +16 more
TL;DR: Some of the recent experimental and theoretical advances in knowledge of the properties of aqueous interfaces are reviewed and open questions and gaps in understanding are discussed.
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Anionic and cationic Hofmeister effects on hydrophobic and hydrophilic surfaces.
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Simulation and Theory of Ions at Atmospherically Relevant Aqueous Liquid-Air Interfaces
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References
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The Hofmeister effect and the behaviour of water at interfaces.
TL;DR: 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 is proposed; this mechanism suggests a simple model for the behaviour of water at all interfaces, regardless of whether the non-aqueous component is neutral or charged, polar or non-polar.
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Statistically optimal analysis of samples from multiple equilibrium states
TL;DR: The multistate Bennett acceptance ratio estimator (MBAR) as mentioned in this paper is an estimator for computing free energy differences and thermodynamic expectations as well as their uncertainties from samples obtained from multiple equilibrium states via either simulation or experiment.
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Statistically optimal analysis of samples from multiple equilibrium states
TL;DR: A new estimator for computing free energy differences and thermodynamic expectations as well as their uncertainties from samples obtained from multiple equilibrium states via either simulation or experiment is presented, which has significant advantages over multiple histogram reweighting methods for combining data from multiple states.
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‘Zur Lehre von der Wirkung der Salze’ (about the science of the effect of salts): Franz Hofmeister's historical papers
TL;DR: In a seminal series of papers, Franz Hofmeister, Professor of Pharmacology at the University of Prague, was the first to study specific ion effects systematically as discussed by the authors, which stands in the scheme of things in importance much as did the work of Mendel to genetics.
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Ions at the Air/Water Interface
TL;DR: In this article, the authors present results from theoretical studies of aqueous ionic solvation of alkali halides aimed at developing a microscopic description of structure and dynamics at the interface between air and saliency.