A Microscopic Model of Gemini Surfactants: Self-assemblies in Water and at Air-Water Interface

TL;DR

This study uses large-scale Monte Carlo simulations to explore how microscopic parameters of gemini surfactants influence their self-assembly in water and at the air-water interface, revealing trends consistent with experimental data.

Contribution

It introduces a detailed microscopic model of gemini surfactants and systematically investigates how molecular features affect aggregation and interfacial organization.

Findings

Counter-intuitive trends in CMC variation explained

Effects of molecular shape and size on micelle formation

Conformational behavior near the air-water interface

Abstract

We report the results of large scale Monte Carlo (MC) simulations of novel microscopic models of gemini surfactants to elucidate (i) their spontaneous aggregation in bulk water and (ii) their spatial organization in a system where water is separated from the air above it by a sharp well defined interface. We study the variation of the critical micellar concentration (CMC) with the variation of the (a) length of the spacer, (b) length of the hydrophobic tail and (c) the bending rigidity of the hydrocarbon chains forming the spacer and the tail; some of the trends of variation are counter-intuitive but are in excellent agreement with the available experimental results. Our simulations elucidate the effects of the geometrical shape, size and density of the surfactant molecules, the ionic nature of the heads and hydrophobicity/hydrophilicity of the spacer not only on the shapes of the micellar aggregates and the magnitude of the CMC, but also on their conformations close to the air-water interface.