MOLECULAR-DYNAMICS SIMULATIONS OF MODEL MICELLES .4. EFFECTS OF CHAIN-LENGTH AND HEAD GROUP CHARACTERISTICS

Molecular dynamics has been used to study the effect of chain length and head group properties on the internal micelle structure, micellar shape, and chain conformation inside the micelle. Simulations of aggregates with 24 octyl chains with "polar methyl" heads, 24 octyl chains with "nonionic sulfate" heads, 52 dodecyl chains with "polar methyl" heads, and 24 nonyl chains were performed. The forces of the skeletal chains involved intramolecular effects of bond vibration, angle bending, and rotation among quartets of adjacent segments, Lennard-Jones interactions between other segments on the chain and those on other chains, and a dipolar potential for head-head interactions. Solvent effects on the aggregate have been modeled with a variety of aggregate boundary forces so that solvent molecules need not be used explicitly. The results give aggregate cores with a structure that is hydrocarbon-like, though the local structure in micelles and hydrocarbon droplets depends on the head group size, the chain length, and the micelle-solvent model. The average aggregate shape is somewhat nonspherical, independent of head group size and surfactant chain length. Chain conformations are substantially the same in all micelle and hydrocarbon droplet simulations. © 1990 American Chemical Society.