Thermal noise properties of two aging materials

TL;DR

This paper investigates the thermal noise in aging polymer and colloidal glass, revealing intermittent electric noise and FDT violations during aging, with results aligning with models predicting intermittent dynamics.

Contribution

It provides new experimental insights into electric and mechanical noise behaviors in aging materials, highlighting intermittency and FDT violations during aging processes.

Findings

Electric noise shows strong intermittency and FDT violation during aging.

Intermittent dynamics are observed in electric noise, consistent with recent aging models.

Mechanical noise results are inconclusive, with some intermittency in polymer but not in gel.

Abstract

In this lecture we review several aspects of the thermal noise properties in two aging materials: a polymer and a colloidal glass. The measurements have been performed after a quench for the polymer and during the transition from a fluid-like to a solid-like state for the gel. Two kind of noise has been measured: the electrical noise and the mechanical noise. For both materials we have observed that the electric noise is characterized by a strong intermittency, which induces a large violation of the Fluctuation Dissipation Theorem (FDT) during the aging time, and may persist for several hours at low frequency. The statistics of these intermittent signals and their dependance on the quench speed for the polymer or on sample concentration for the gel are studied. The results are in a qualitative agreement with recent models of aging, that predict an intermittent dynamics. For the mechanical noise the results are unclear. In the polymer the mechanical thermal noise is still intermittent whereas for the gel the violation of FDT, if it exists, is extremely small.