Molecular Dynamics Simulation of the Adsorption and Aggregation of Ionic Surfactants at Liquid–Solid Interfaces

Abstract

Structure of surfactants adsorbed on solid surfaces is a key knowledge in various technologies and applications. It is widely accepted in the literature that the surface–surfactant headgroup electrostatic interaction is a major driving force of adsorption of ionic surfactants on charged substrates. Our result shows that the adsorption of surfactants as monomers is driven by both electrostatic and nonelectrostatic interactions. Further adsorption of surfactants in aggregates is essentially driven by the tail–tail interaction. To a great extent, the substrate–tail interaction determines the structures of the adsorbed surfactant aggregates. Water and counterions influence the headgroup–substrate and tail–substrate interactions. We investigate two vastly different surfactants and substrates by molecular dynamics simulations: (1) SDS on alumina (SDS–Al2O3), and (2) CTAB on silica (CTAB–SiO2). We study the adsorption of a single surfactant at the solid surface by the density profiles and free energy of adsorpti...