THE PHENOMENON OF WATER PENETRATION INTO SODIUM OCTANOATE MICELLES STUDIED BY MOLECULAR-DYNAMICS COMPUTER-SIMULATION

In this publication we have studied the penetration process of water m olecules into the hydrophobic core of a sodium octanoate micelle. The analysis of this phenomenon was based on a molecular dynamics computer simulation. We calculated the probability to find water molecules wit hin a specific sphere which was adjusted in the center of the micelle. It turned out that the position of the micellar mass and geometry cen ter was not too different, so that this reference point was well chara cterized. Water penetration was observed within the whole aggregate bu t if the radius is smaller than 300 pm, polar solvent molecules are ve ry rarely observed. The results of our computer simulations suggest th at significant water diffusion into the micelle occurs at larger dista nces from the micellar center with a lower threshold value of about 40 0 pm. In addition to these calculations, we used the Connolly algorith m in order to determine the solvent accessible surfaces of different m icellar equilibrium structures. We observed large dynamical fluctuatio ns with the formation of pores and channels. These structures are occa sionally filled with water molecules.