Coarse-Grained Force Field for Ionic Surfactants

Wataru Shinoda, Russell DeVane, and Michael L. Klein

Soft Matter, 7, 6178-6186 (2011).

We present a new coarse-grained (CG) molecular model for ionic surfactants, which is compatible with previously developed CG models for nonionic surfactants and lipids. The CG force field is described by rather simple interaction functions including a separate non-truncated Coulomb interaction term between charged segments. The CG surfactant model reproduces experimental surface tension and density as well as distribution functions from all-atomic molecular models. A CG molecular dynamics simulation of sodium dodecyl sulfate (SDS) micellar solution produces a reasonable distribution of monomers between micelles and bulk solution. The SDS model is used to investigate the effect of salt on micelle size and adsorption on a carbon nanotube; studies which help elucidate the applicability and transferability of the present CG model. Trial computations on a Langmuir monolayer of ionic surfactants illustrate how truncation of the Coulomb interaction can significantly influence the counter ion distribution.