Tracking Coupled Granular Temperature and Entropy Dynamics in Granular Materials via Dielectric Spectroscopy

TL;DR

This study demonstrates that dielectric spectroscopy can effectively track the coupled dynamics of granular temperature and entropy in granular materials, following an Adam-Gibbs-like relationship, thus providing a new non-destructive probing method.

Contribution

It introduces a novel application of dielectric spectroscopy to measure configurational entropy and granular temperature in granular matter, extending thermodynamic models to athermal systems.

Findings

Dielectric relaxation time scales with granular temperature and entropy.

Packing fraction variations influence impedance in accordance with an Adam-Gibbs-like law.

Dielectric spectroscopy serves as a non-destructive probe of granular configurational dynamics.

Abstract

In glass-forming liquids, structural dynamics are governed by configurational entropy and temperature, with dielectric relaxation time scaling alongside structural relaxation time as described by the Adam-Gibbs (AG) model. Under Edwards's athermal statistical thermodynamics, a modified AG law similarly governs granular matter, provided that granular temperature and configurational entropy are appropriately defined. This study investigates whether variations in the structural relaxation of granular systems can be probed via thermally activated processes, specifically electric charge hopping and trapping. By progressively reducing the volume of graphite powder to vary its packing fraction, we estimated relative configurational entropy and granular temperature from volumetric data, while evaluating electrical conductivity and capacity via impedance spectroscopy. We demonstrate that the logarithm of the dielectric relaxation time, derived from complex impedance, scales with granular temperature and entropy across both loose and compact states. Consequently, changes in the complex impedance resulting from packing fraction variations are tuned by granule configuration, strictly adhering to an AG-like relationship for thermal systems. These findings establish dielectric spectroscopy as a viable, non-destructive tool for tracing configurational dynamics in granular matter, analogous to its established use in polymers and glass formers.