Intentionally added ionic surfactants induce Jones-Ray effect at air-water interface

TL;DR

This study demonstrates that the Jones-Ray effect in water surface tension can be induced by adding ionic surfactants, supported by experimental data and Poisson-Boltzmann theory, indicating contamination as a key factor.

Contribution

It provides experimental and theoretical evidence that ionic surfactants induce the Jones-Ray effect, clarifying the role of contamination at the air-water interface.

Findings

Ionic surfactants induce the Jones-Ray effect.

Poisson-Boltzmann theory agrees with experimental data.

Contamination likely causes the observed effect.

Abstract

The Jones-Ray effect is an anomalous minimum in the surface tension of aqueous electrolytes at millimolar salt concentrations. We experimentally demonstrated that intentionally added ionic surfactants induce the Jones-Ray effect. The one-dimensional Poisson-Boltzmann theory, including the effect of surfactant adsorption and salt depletion, excellently agrees with the obtained experimental data. All the parameters of the ion-specific surface affinities used in the theory are consistent with previous experiments. These results strongly suggest that the Jones-Ray effect observed so far has been induced by the inevitable contamination of the air-water interfaces.