Broadband Dielectric Spectroscopy in nano-(bio)-physics

摘要

Broadband Dielectric Spectroscopy as one of the major tools in molecular physics benefits from the extraordinary advantage that its sensitivity increases with decreasing thickness of a sample capacitor and hence with a decreasing amount of sample material. This enables one for instance to carry out broadband spectroscopic measurements on quasi-isolated polymer coils in nano-structured capacitor arrangements, having thicknesses as small as 10 nm. It is demonstrated that for polymers like atactic poly-(methyl methacrylate) (PMMA) or poly-2-vinyl-pyridine (P2VP) the dynamic glass transition can be measured for (averaged) sample thickness as small as ~ 2 nm in a wide spectral range (10 mHz to 10 MHz) and at temperatures between 150 K to 350 K. No shift of the mean relaxation rate and no broadening of the relaxation time distribution function are found compared to the bulk liquid. — Electrode polarization is a ubiquitous phenomenon which takes place at the interface between a metal and an ionic conductor. A quantitative theory will be presented, which enables one to deduce from its characteristic frequency, temperature and concentration dependencies — by use of a novel formula — the bulk conductivity of the ion conducting liquid under study. It is shown that the electrical relaxation processes take place within a nanometric layer at the (ionic conductor/metal) interface which can be analysed in detail.