MOLECULAR-DYNAMICS SIMULATION STUDY OF AN N-DECYLTRIMETHYLAMMONIUM CHLORIDE MICELLE IN WATER

A molecular dynamics (MD) simulation study of a n-decyltrimethylammoni um chloride micelle in water is presented. The model system contains 3 0 amphiphile molecules, 30 chloride ions, and 2166 water molecules. We use the same model potentials as in a recent MD study of a n-hexadecy ltrimethylammonium chloride monolayer in water (Bocker, J.; Schlenkric h, M.; Bopp, P.; Brickmann, J. J. Phys. Chem. 1992, 96, 9915). The mai n objective of this work is to analyze the shape and the structure of the micelle. A slightly prolate ellipsoidal shape of the micelle emerg es from a simulation of 275 ps. It is found that the interior is compl etely ''dry''. This result is in contrast to monolayers-aqueous soluti on interfaces (Bocker, J.; Schlenkrich, M.; Bopp, P.; Brickmann, J. J. Phys. Chem. 1992, 96, 9915). A molecularly sharp interfacial region a ppears, in agreement with experimental studies. The charges on the sur face of the micelle are only partially neutralized by chloride counter ions in the first solvation shells of the head groups. The area per he ad group on the micelle surface and the orientations of the alkyl chai ns as obtained from the simulation are in accord with experimental res ults.