From the time the molecular dynamics (MD) simulation technique was first applied to surfactant assemblies, numerous studies on surfactants with computational tools has been carried out. The size-dependent free energy of association for micelle-forming surfactants controls the critical micelle concentration and the concentration-dependent distribution of micelle sizes. We have developed an analysis approach (PEACH method) to calculate cluster free energy profiles from cluster statistics of molecular dynamics simulations with only one or two micelles. This research project aims to investigate into the fundamental thermodynamics of the micellization process of several typical fatty acid surfactants. Regarding this type of surfactants, experimental results from different techniques have shown inconsistent or contradictory properties of average micelle sizes, critical micelle concentration and counterion binding affinity. In this project, we simulate the equilibrium behaviors of octanoate/decanoate micelles with Na+ and K+. Using PEACH, we obtained the cluster free energy profiles with respect to cluster sizes and number of bound counterions. Free energies of assembly were consistent with simple phenomenological models, whose parameters were used to generate enthalpograms that are comparable to experimental results from isothermal titration calorimetry (ITC). By taking into account the full range of clusters formed, the phenomenological models may prove effective in resolving experimental inconsistencies.

Molecular dynamics study on the micellization of carboxylate surfactants

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.