STRUCTURE AND DYNAMICS OF WATER IN THE PRESENCE OF CHARGED SURFACTANTMONOLAYERS AT THE WATER-CCL4 INTERFACE - A MOLECULAR-DYNAMICS STUDY

We have performed molecular dynamics simulations of sodium dodecyl sul fate (SDS) and a model cation at the water-CCl4 interface at a coverag e of 45 Angstrom(2)/molecule. In order to isolate the effects due to t he polarity of the surfactant, the model potential for the cationic su rfactant is chosen to be identical to that of SDS except that the sign of all atomic charges, including counterions, are reversed. We show t hat the structural features of the two types of surfactant monolayers give rise to large differences in the surface potential profiles and i n the overall potential difference across the water-surfactant-CCl4 in terface. In addition, we show that water in intimate contact with the ionic layer is significantly altered in terms of its dynamic al proper ties-a decrease of up to 1 order of magnitude in the rotational correl ation time for the water dipole reorientation is observed. We also sho w that water orientational polarization propagates well into the bulk region and that this polarization depends on the sign of the ionic sur factant.