Molecular dynamics simulation study of sodium dodecyl sulfate micelle: Water penetration and sodium dodecyl sulfate dissociation

Abstract

Abstract We investigate a micelle consisting of 60 sodium dodecyl sulfate (SDS) molecules in water phase using molecular dynamics simulation method. The dimension of the micelle is evaluated as ∼16 A and ∼21 A for the radius of gyration and geometric radius, respectively, which are well agreed with the previous studies. By calculating the formation energy, it is found that the stability of micelle is driven by the interaction of the micelle with water phase. Via Connolly surface analysis, it was found that ∼58% of the micelle surface is occupied by the hydrophobic alkyl tails. The conformation analysis shows that the individual SDS molecules are bent within the micelle and are not aligned radially from the center-of-mass of the micelle. However, it turns out that the micelle is well packed with a small free volume (0.35% of the micelle volume) which does not allow the diffusion-in of water molecules. The PMF required to drag a water molecule from water phase to the center-of-mass of micelle is calculated as ∼10 kcal/mol while the PMF for a SDS molecule to be dissociated from the micelle is ∼13 kcal/mol, both of which demonstrate that the micellization is driven by minimizing unfavorable interaction of hydrophobic alkyl tail of SDS molecule with water phase.