Dielectric spectroscopy of polymer-metal composites across the percolation threshold

摘要

Polymer (polaronpolar)/metal composites (PMC) were prepared under different process conditions. In polar PMC, dipolar relaxation plays a predominant role below percolation threshold (f_c) and anomalous low frequency dispersion (ALFD) becomes dominant above f_c while ALFD is the only likely possibility for nonpolar PMC above f_c. The magnitude of relaxation exponents "m", "p" and "n", evaluated from the experimental results using Jonscher's universal dielectric response (JUDR) laws, falls within the universal limit ～ [0, 1] with additional feature of strong dependence on volume fraction of conductor (f_(con)). The decrease in the relaxation exponent "m" with an increase of f_(con) is directly linked with decrease in the number of dipoles of the polymer in the composite and is accompanied by a distribution of relaxation time due to increased heterogeneity of the system. The magnitude of the relaxation exponent "n" decreases at f_c, due to the prevalence of Maxwell-Wagner-Sillar polarization contributed by uncorrelated electrons.