Surface-bulk partition of surfactants predicted by molecular dynamics simulations

The surface-bulk partition of surfactants is a piece of important information for understanding the performance of surfactants. In this work, we predicted surface-bulk partitions for three ionic surfactants (sodium hexyl sulfate, sodium nonyl sulfate, sodium dodecyl sulfate) using molecular dynamics simulations and a coarse-grained force field. The simulations were performed with the bilayer model that represents thin films. By setting initial configurations using chemical potentials calculated for infinitely dilute solutions, we obtained a sufficient number of independent samples for each simulation which ran at least 2 μs. Predicted surface concentrations and surface tensions are in good agreement with the experimental data. The surface adsorption isotherms, surface structures, and critical micelle concentrations (CMCs) derived from the simulated data are in reasonable agreement with the experimental data and previously calculated data. For surfactants with a short alkyl chain (SHS), stable oligomers are formed before micelles in the bulk.