Interaction with sodium dodecyl sulfate aqueous systems

Previously, the sodium dodecyl sulfate (SDS) surfactant system was also investigated with a 200 ps molecular dynamics computer simulation in the NVT-ensemble (7). In this computer simulation, the parameters of the atomic interaction potential functions were taken from the CHARMM force field. The calculations showed that the SDS micelle remains spherical with a radius of gyration in good agreement with the experimental results. Remarkable motions of the head-groups were observed and the trans to gauche populations are equivalent for the micelle and the analogous hydrocarbon, liquid dodecane. Recently, atomic-level studies of AOT reverse micelles and molecular dynamics simulations of the structure and dynamics of a dode-cylphosphocholine micelle in aqueous solution have been published (8, 9). 

Figure 4.21 shows the values for aqueous solutions of various alcohols—from methanol to butanol—which represent a continuous spectrum of values of the free energy of interaction. Very similar results were observed in the case of an aqueous solution of a classic anionic surfactant— sodium dodecyl sulfate (Figure 4.22). In this case, one is dealing with a fully reversible true equilibrium system. The same behavior was also observed for a cationic surfactant, cetylpyridinium bromide (CPB) (Figure 4.23), and to some extent, in a solution of a nonionic surfactant, polyoxyeth-ylated ether (Figure 4.24). In the latter case, however, the system is a nonequilibrium one there is a dependence of the measured pi value on time.

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