Nonionic and ionic surfactants at an interface

TL;DR

This paper develops a Ginzburg-Landau theoretical framework to analyze the distribution and effects of ionic and nonionic surfactants at interfaces in polar binary mixtures, including electrostatic and solvation interactions.

Contribution

It introduces a comprehensive model incorporating solvation, image interactions, and finite surfactant volume to predict surfactant distributions and surface tension at interfaces.

Findings

Ionic surfactants have narrower distributions than counterions.

Adsorption varies significantly between hydrophilic and hydrophobic pairs.

The model predicts electric potential and surface tension changes at interfaces.

Abstract

A Ginzburg-Landau theory is presented on surfactants in polar binary mixtures, which aggregate at an interface due to the amphiphilic interaction. They can be ionic surfactants coexisting with counterions. Including the solvation and image interactions and accounting for a finite volume fraction of the surfactant, we obtain their distributions and the electric potential around an interface in equilibrium. The surface tension is also calculated. The distribution of the adsorbed ionic surfactant is narrower than that of the counterions. The adsorption is marked for hydrophilic and hydrophobic pairs of ionic surfactant and counterions.