Experimental study of out of equilibrium fluctuations in a colloidal suspension of Laponite using optical traps

TL;DR

This study investigates the displacement fluctuations of micron-sized particles in an aging colloidal glass, examining the validity of the fluctuation dissipation theorem and the evolution of viscoelastic properties using combined passive and active microrheology techniques.

Contribution

It demonstrates the compatibility of passive and active microrheology in aging colloidal glasses and confirms the validity of the fluctuation dissipation theorem during aging.

Findings

No violation of FDT observed during aging.

Passive and active microrheology techniques yield compatible results.

Long time correlations and statistical properties evolve during transition.

Abstract

This work is devoted to the study of displacement fluctuations of micron-sized particles in an aging colloidal glass. We address the issue of the validity of the fluctuation dissipation theorem (FDT) and the time evolution of viscoelastic properties during aging of aqueous suspensions of a clay (Laponite RG) in a colloidal glass phase. Given the conflicting results reported in the literature for different experimental techniques, our goal is to check and reconcile them using \emph{simultaneously} passive and active microrheology techniques. For this purpose we measure the thermal fluctuations of micro-sized brownian particles immersed in the colloidal glass and trapped by optical tweezers. We find that both microrheology techniques lead to compatible results even at low frequencies and no violation of FDT is observed. Several interesting features concerning the statistical properties and the long time correlations of the particles are observed during the transition.