Restructuring of Hydrophobic Surfaces Created by Surfactant Adsorption to Mica Surfaces

Entry by Yuhang Jin, AP225 Fall 2011

Reference

Jhuma Das, Changsun Eun, Susan Perkin, and Max L. Berkowitz, Langmuir, 2011, 27, 11737.

Keywords

Surfactant monolayer, hydrophobic surfaces, long-range electrostatic interaction, molecular dynamics simulation

Introduction

Hydrophobic interaction acting between surfaces is important in many fields and applications. Sometimes this interaction can act over distances as large as ~50 nm, probably due to the existence of submicroscopic bubbles, cavitation in the intervening fluid, or electrostatic interactions between charged patch of restructured hydrophobic surfaces created by surfactant adsorption to mica. Using a surface force balance (SFB), one can measure the interaction between hydrophobic surfaces created by placing ionic surfactants on mica. The interaction sometimes displays a long-ranged hydrophobic component owing to the coexistence of both negatively charged bare mica patches exposed to water and positively charged patches covered by a surfactant bilayer. In this paper, computer simulations confirmed this picture and studied how this restructuring depends on the properties of the surfactant molecules.

Simulations and results

Fig.1 Initial structure of the simulated model. Green spheres: surfactant headgroups; blue licorice: surfactant tails; red spheres: chloride ions; tan spheres: potassium ions; magenta licorice: mica sheets; gray CPK: water box.