Self assembly of model surfactants as reverse micelles in nonpolar solvents and their role as interfacial tension modifiers

TL;DR

This study uses simulations to explore how surfactants self-assemble into reverse micelles in nonpolar solvents like oil and scCO2, affecting interfacial tension and viscosity, with findings aligning with experimental data.

Contribution

It provides a detailed simulation-based analysis of reverse micelle formation and surfactant efficiency in nonpolar solvents, including the role of water molecules, which is novel.

Findings

Reverse micelles form more easily in oil than in scCO2.

Adding water enhances reverse micelle formation.

Surfactants reduce interfacial tension mainly by adsorbing at interfaces.

Abstract

The self assembly of linear surfactants into reverse micelles (RMs) in nonpolar solvents and their efficiency in reducing the interfacial tension is studied using dissipative particle dynamics simulations. Given the importance of RMs as thickeners, among many other applications, their properties are studied here when formed in oil and in supercritical carbon dioxide (scCO2). Our simulations are found to be in agreement with experimental results of surfactant self assembly in scCO2 that found viscosity increments of up to 90 percent with 10 wt percent of surfactants. The role played by a small number of water molecules in RM formation is studied as well in both solvents, corroborating experiments reporting the enhancement of RM formation with the addition of a small quantity of water. The dynamics of water surfactant aggregation in nonpolar solvents is also discussed. Lastly, the performance of the model surfactant as an interfacial tension modifier is studied in detail. The results show that RMs are more easily formed in oil than in scCO2 and that the effectiveness of the surfactant in reducing the interfacial tension lies in its preference to adsorb at interfaces rather than self association.