Although adsorption isotherms of surfactants are critical in determining the relationship between the interfacial properties and structures of surfactants, providing quantitative predictions of the isotherms remains challenging. This is especially true for adsorption at hard interfaces such as on 2D layered materials or on nanoparticles where simulation techniques developed for fluid-fluid interfaces do not apply. In this work, we predict non-ideal adsorption at a solid-solution interface with a molecular thermodynamic theory (MTT) model that utilizes molecular dynamics (MD) simulations for the determination of free energy parameters in the MTT. Furthermore, the MTT/MD model provides atomistic insights into non-ideal behavior of surfactant molecules by capturing structural phases of the surfactants at different concentrations. Our approach captures structural transitions from the ideal state at low concentrations and then to the critical surface aggregation concentration (CSAC) and finally through the critical micelle concentration (CMC). We validate our model against the original MTT model by comparing predicted adsorption isotherms of a simplified surfactant system from both approaches. We further substantiate the applicability of our model in complex systems by providing the adsorption isotherms in an aqueous sodium dodecyl sulfate(SDS)-graphene system, in good agreement with experimental observations of the CSAC for the same system.

Capturing structural transitions in surfactant adsorption isotherms at solid/solution interfaces

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.