Despite their simple topology, surfactant structures are extremely diverse, from simple organosulfate detergents to complex glycolipids. Widespread use makes surfactants one of the most versatile chemicals known, however, current understanding of surfactant properties is mostly empirical. Research in my group seeks to establish structure-dynamics relations by mapping out the hydrophobic/hydrophilic interfacial environment under a variety of conditions. Ester carbonyl vibrations are useful probes of local dynamics since they are located precisely at the interface between hydrophilic and hydrophobic environments. Interfacial water has been shown to be slower than bulk, but the relationship between water and surfactant dynamics is not well understood.<br/><br/>In this talk, I will present recent results on ~100 nm oil-in-water reverse micelles prepared using nonionic sorbitan surfactants. Hydrogen-bond populations and dynamics are measured using two-dimensional infrared (2D IR) spectroscopy of the surfactant ester C=O modes. Spectra show that interfacial hydrogen bond populations are similar to C=O in bulk water, but hydrogen-bond switching rates are ~3x slower at the interface. In high concentrations, divalent cations such as Ca2+ significantly increase disorder and hydration, but surprisingly hydrogen-bond lifetimes are not affected.<br/><br/>Increasingly accurate molecular dynamics simulations provide a structural interpretation of the experiments. In this talk, I will describe our recent progress in benchmarking MD models and simulations against experiment. In addition, I will describe a recently-developed spectroscopic map to directly generate 2D IR spectra MD trajectories.

Ultrafast two-dimensional infrared spectroscopy of disordered surfactant interfaces

255th National Meeting (2018)

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