Shooting lasers at soap : ultrafast dynamics at surfactant interfaces

Surfactants, by virtue of their amphiphilicity, are used in a wide array of industries to solubilize and stabilize heterogeneous mixtures. However, despite their everyday use, the fundamental physical chemistry of these molecules is still poorly understood. To characterize the molecular interactions that give rise to desirable bulk properties, we use a combination of linear and ultrafast, two-dimensional vibrational spectroscopies in conjunction with molecular dynamics simulations. Together, these methods afford femtosecond temporal resolution and atomistic structural resolution, enabling us to quantify the type and number of intermolecular interactions. Sub-picosecond time resolution also enables us to measure the dynamics of these processes. By observing the surfactant-water interface, we show how detergent interactions with oil, aqueous media, and other surfactants all contribute to the interfacial environment.