Knowledge of the self-assembly and phase behavior of pH-sensitive surfactants has implications in many technological applications such as formulation of detergents and development of drug delivery vehicles. The recently developed continuous constant pH molecular dynamics (CpHMD) technique has opened a door to atomic-level understanding of such phenomena. As a proof a principle study, we applied CpHMD to simulate the self-assembly of 12-carbon fatty acids. We observed the formation of a micelle at high pH and a bilayer at low pH, as seen in experiment. Both the micelle-bilayer transition pH as well as the apparent pKa values are in quantitative agreement with experiment. Additional data show that aggregates containing more fatty acids have a higher pKa, and decreasing the tail length decreases the pKa. We have also studied the titration behavior of fatty acids in bilayers of 18-carbon surfactants. These results give novel insights into the interplay between protonation, conformational dynamics and phase transitions.

Self-assembly and phase behavior of pH-sensitive surfactants

246th National Meeting (2013)

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