Molecular dynamics studies of the hexagonal mesophase of sodium dodecylsulphate in aqueous solution

Abstract

Molecular dynamics calculations using a recently proposed simulation methodology (Martyna, G. J., Tuckerman, M. E., Tobias, D. J., and Klein, M. L., 1996, Molec. Phys., 87, 1117) have been carried out to investigate the structural properties of the sodium dodecylsulphate (SDS)-water system in the lyotropic liquid crystalline mesophase E. The simulation system consisted of two cylindrical aggregates, each containing 128 dodecylsulphate anions, plus 256 sodium counterions and 4350 water molecules. The system had periodic boundary conditions and initially overall hexagonal symmetry. A 260ps trajectory was then generated at constant temperature (T = 333 K) and constant pressure (P = 0) using a new molecular dynamics package (PINY-MD), which utilizes a timestep almost an order of magnitude larger than the usual value. The structural and dynamic results are compared with previous simulations reported for quasi-spherical SDS micelles and experimental data on the same system. In agreement with experiment, the simulation predicts a small but well-defined distortion from hexagonal symmetry.