Universal microstructure and conductivity relaxation of polymer-conductor composites across the percolation threshold

Micro-structural and impedance analysis of series of insulating polymer/conductor composites (PCC) as a function of frequency and volume fractions of the conductor (fcon) have been studied. Evidences of conductivity relaxation have been noticed with a correlation with the sample micro-structure. This has been understood and explained in terms of equivalent electrical circuit model of the material established through complex impedance spectroscopy (CIS) across the percolation threshold (fc) for all the PCC. CIS analysis confirmed that PCC with fcon ≥ fc, exhibit conductivity/interfacial relaxation due to polarization of Maxwell–Wagner–Sillars (MWS) type at fc and the relaxation frequency increases with increase of fcon. The modulus spectroscopy analysis suggests the presence of two types of relaxations in different frequency ranges; (i) dipolar relaxation associated with the flipping of dipoles present in the pure polymer for fcon < fc and (ii) the conductivity/interfacial relaxation due to the formation of artificial MWS dipoles at the interface of the two components. A long range dc conductivity appears at fcon ≥ fc and Jonschers universal fractional power law is satisfied for both the regions of fcon < fc and fcon ≥ fc in all PCC.