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 molecules 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 within a specific sphere which was adjusted in the center of the micelle. It turned out that the position of the micellar mass and geometry center was not too different, so that this reference point was well characterized. Water penetration was observed within the whole aggregate but if the radius is smaller than 300 pm, polar solvent molecules are very rarely observed. The results of our computer simulations suggest that significant water diffusion into the micelle occurs at larger distances from the micellar center with a lower threshold value of about 400 pm. In addition to these calculations, we used the Connolly algorithm in order to determine the solvent accessible surfaces of different micellar equilibrium structures. We observed large dynamical fluctuations with the formation of pores and channels. These structures are occasionally filled with water molecules.