Simulation of sodium dodecyl sulfate at the water-vapor and water-carbon tetrachloride interfaces at low surface coverage

To study the effect of the interface on the properties of an anionic surfactant molecule, sodium dodecyl sulfate (SDS), we performed two molecular dynamics computer simulations. In one simulation, the behavior of SDS at the water-vapor interface was examined. In parallel, we performed a simulation with the molecule embedded at the water-CCl4 interface. A substantial difference in the configurational properties of the amphiphile was observed. At the water-vapor interface, the solute in its most probable configuration was bent, giving rise to two domains within the molecule: the first, containing the head group and several methyl groups, was solvated in water; the second, containing the rest of the molecule, lay down on the water surface. In contrast to these results, the molecule at the water-CCl4 interface was straight on average, with a inclination of approximately 40 degrees from the surface normal.