Broadband dielectric relaxation spectroscopy at 10~(-4) - 10~(10) Hz

摘要

Dielectric relaxation spectroscopy (DRS) has been developed over the last decades into a powerful tool for the investigation of molecular mobility in a variety of materials. Its main advantage over other spectroscopic methods is the extremely broad frequency range of 14 - 15 decades which can be rather easily covered. Mechanisms which contribute to the DRS spectra include dipolar relaxation, conductivity relaxation, space charge relaxation, and interfacial or Maxwell-Wagner-Sillars relaxation in inhomogeneous materials. A detailed study of these relaxation mechanisms provides information on the structure at the molecular level, the morphology at the level of mesoscopic dimensions and the dynamic properties of the material under investigation. To demonstrate the wide applicability of DRS to various topics in materials science, results on three systems are briefly described: poly(hydroxyethyl acrylate) (PHEA) hydrogels, water and glass-forming liquids in confined geometries, and polyurethane block copolymers and blends. The results are discussed in terms of polymer -water interactions, hydrophilic and hydrophobic confinement, the cooperative character of glass transition, percolation, phase mixing and phase separation in copolymers and blends.