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Abstract
Recent vibrational sum frequency generation spectroscopic experiments (J. Phys. Chem. Lett. 13, 11391–11397 (2022)) demonstrated synergistic interfacial adsorption effects between the anionic dodecyl sulfate (DS-) and the polar, but charge-neutral hexaethylene glycol monododecyl ether (C12E6) surfactants. In this study, the interfacial adsorption thermodynamics underlying these synergistic effects are analyzed through free energy decompositions. A general decomposition method utilizing alchemical intermediate states is outlined. Combining free energy decompositions with the potential distribution theorem illuminates the statistical interpretations of correlated effects between different system components. This approach allows for the identification of the physical effects leading to synergistic adsorption thermodynamics of DS- binding to the air-C12E6-water interface. The binding properties are found to result from a combination of effects predominantly including energetic van der Waals stabilization between DS- and C12E6, as well as competing energetic and entropic effects due to changes in the interfacial water structure as a result of introducing a C12E6 monolayer into the bare air-water interface.
Supplementary materials
Title
SI to Free Energy Decompositions Illuminate Synergistic Effects in Interfacial Binding Thermodynamics of Mixed Surfactant Systems
Description
The supplementary materials include: the density profiles of the C12E6 and the water at the air-C12E6-water interface (ACWI) and at the bare air-water interface (AWI), the error analysis for the umbrella sampling free energy profiles and solute-solvent energy averages, water coordination of DS- head groups as a function of z at the ACWI and the AWI, and orientational entropy profiles for DS- at the ACWI and the AWI.
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