The far infrared dielectric properties of confined water
Boyd, Joel E.
Colvin, Vicki L.
Doctor of Philosophy
The far infrared dielectric properties of confined water were measured with terahertz time-domain spectroscopy. Inverse micelles with anionic, cationic, as well as non-ionic surfactants were used to confine the water with excellent size control from water pool radii of 5 to 75 angstroms. The normally flat far infrared absorption spectra of water is profoundly disrupted by confinement, yielding spectra with very large absorption peaks between 0.2 and 1.0 THz. These peaks are present in all surfactant systems as well as in samples formulated with various brine concentrations or glycerol in place of the water. The origin of the THz absorptions of these liquid pools is assigned to surface oscillations of the water pool opposed by the interfacial tension of the water-surfactant-oil interface. The implications of the existence of this peak are quite important. The far infrared dielectric properties of confined water are important in many biological and inorganic systems ranging from protein folding to zeolite chemistry. Additionally, the spectral position and lineshape of these absorption peaks are suggestive of a similar phenomenon in glass forming materials known as the Bose peak. This peak in the far infrared is believed to be due to coherent scattering off of various domains of homogeneity within the inhomogeneous glass. A size-dependent study of these domains in glasses is frustrated by an inability to control domain size within a single glass system. The amenability of inverse micelles to a size dependent study, and the surprising degree of correlation between the lineshapes of the Bose peak with the absorption spectra of micellar confined water, indicate that these results could have great importance in understanding the origins of the Bose peak in glassy materials.