Computer studies on the effects of long chain alcohols on sodium dodecyl sulfate (SDS) molecules in SDS/dodecanol and SDS/hexadecanol monolayers at the air/water interface

Molecular dynamics simulations of sodium dodecyl sulfate (SDS)/dodecanol and SDS/hexadecanol monolayers at the air/water interface were investigated where the monolayer mixtures were prepared by two different configurations. In the first configuration, all of the dodecanol (or hexadecanol) molecules were placed together and also the SDS molecules were placed together in the surface area. In the second configuration, the dodecanol (or hexadecanol) molecules were uniformly distributed with the SDS molecules, forming a homogeneous mixture. The results showed that the alcohol tails are more ordered and thicker than the SDS tails in monolayers where the alcohol molecules are close to each other and separated from the SDS. However, the reverse trend is observed in monolayers where the SDS and alcohol molecules are well mixed; that is, the alcohol tails seem to have less order. Studies of how the SDS tails are affected by the presence of long chain alcohols are also discussed. Basically, by increasing the alcohol chain length, the order and the thickness of the SDS tails increased when those molecules were placed all together in a region of the surface area. When both surfactants were well mixed, the order and thickness of the SDS chains decreased as the alcohol chain length increased. Comparisons of the present results with actual experiments of similar systems were performed, and they showed similar tendencies.