Surface tensions and surface potentials of acid solutions

TL;DR

This paper introduces a theory to quantitatively predict the excess surface tension of acid solutions, emphasizing hydronium ion adsorption and orientation at the interface, with accurate results for surface tension and qualitative insights for electrostatic potential differences.

Contribution

The paper presents a new theoretical model that accurately calculates surface tensions and explains ion orientation effects at the air-water interface.

Findings

Hydronium ions are strongly adsorbed at the interface.

Ion orientation with hydrogens pointing into water is necessary to match electrostatic potential measurements.

The theory accurately predicts surface tensions of acid solutions.

Abstract

A theory is presented which allows us to quantitatively calculate the excess surface tension of acid solutions. The H^+, in the form of hydronium ion, is found to be strongly adsorbed to the solution-air interface. To account for the electrostatic potential difference measured experimentally, it is necessary to assume that the hydronium ion is oriented with its hydrogens pointing into the bulk water. The theory is quantitatively accurate for surface tensions and is qualitative for electrostatic potential difference across the air-water interface.