Terahertz spectroscopy of water in inverse micelles

We report a study of the dielectric properties of water bound in inverse micelles of sodium bis(2-ethylhexyl)sulfosuccinate (AOT), in heptane, using terahertz time-domain spectroscopy. The size-dependent absorption and dispersion spectra of these nanometer-sized water pools are measured in the spectral range 0.2–2 THz (6–60 cm−1), and are evaluated using a two-component Debye model. The amplitude of the dielectric relaxation in this spectral range is substantially smaller than that observed in bulk water. This is attributed to the effects of the confinement, which disrupt the long-range collective modes normally present in the liquid. An additional higher frequency mode is observed, and its potential origin discussed.