Terahertz Vibrational Modes of Inverse Micelles

A large absorption resonance has been observed in the far-infrared spectrum of water confined within inverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in heptane. The amplitude and spectral position of this resonance depend on the size of the water pool. The origin of the THz absorption of these liquid pools is assigned to surface oscillations of the water pool, driven by the interfacial tension of the water−surfactant-oil interface. These data indicate a dramatic restructuring of the density of states of the liquid and are consistent with a theoretical model for the oscillatory modes of liquid droplets. The presence of a large excess in the vibrational density of states of confined water could have far-ranging implications in many biochemical and chemical processes where confined water is present.