Microwave dielectric relaxation spectroscopy of liquids.

摘要

In this thesis, a new technique, which is non-invasive, fast and accurate, was developed for measuring broadband continuous dielectric spectra of liquids and solids. It was tested from 45MHz to 20GHz but is applicable to at least 40GHz. The technique was used to study a variety of liquid samples in which water was a primary component.;A graphical representation for the complex dielectric data was discovered. It is specially useful for conducting dielectrics, and is sensitive to high frequency features. This makes it possible to graphically visualize multiple relaxation processes with small amplitudes.;The notion of "microwave dielectric excluded volume" was introduced for ionic and biological macromolecular aqueous solutions. This is the volume surrounding the solute molecule which is not able to reorient at microwave frequencies. The number of hydration water molecules around each solute molecule can be extracted from the dielectric excluded volume. Results were obtained on ACl (A = Li, Rb and Cs) and heme protein aqueous solutions. In protein solutions, the partially-opened conformation of met myoglobin obtained by lowering the pH value of the solution seems to have smaller microwave dielectric excluded volume.;The dynamics of alkali-halides aqueous solutions, was extensively studied via dielectric spectroscopy. It was found that the existing kinetic polarization theory does not explain the experimentally observed linear decrease of the solution relaxation time with increasing dc solution conductivity for moderate concentrations, which can however be explained by an empirical viscosity formula and cation size effects. The temperature dependence of the relaxation time and conductivity in concentrated LiCl/H;It was shown, by the dielectric investigation on the concentration dependence of alcohol/water solutions, that alcohol molecules strongly interact with water molecules. The addition of a small amount of alcohol, 1-propanol, ethylene glycol or glycerol to water, or similarly water to alcohol, substantially changes the dielectric behavior of the solvent, which may be the evidence of the "fusion of relaxation channels".