Measurement of Effective Temperatures in an Aging Colloidal Glass

TL;DR

This study measures the effective temperature of a probe particle in an aging colloidal suspension, revealing a significant increase in temperature in the glassy phase compared to the bath temperature, indicating nonequilibrium behavior.

Contribution

It introduces a method to measure effective temperatures in aging colloidal glasses using optical trapping and fluctuation analysis, highlighting nonequilibrium effects.

Findings

In the liquid phase, probe temperature equals bath temperature.

In the glassy phase, probe temperature exceeds bath temperature.

Effective temperature correlates with the aging state of the suspension.

Abstract

We study the thermal fluctuations of an optically confined probe particle, suspended in an aging colloidal suspension, as the suspension transforms from a viscous liquid into an elastic glass. The micron-sized bead forms a harmonic oscillator. By monitoring the equal-time fluctuations of the tracer, at two different laser powers, we determine the temperature of the oscillator, $T_{\text{o}}$. In the ergodic liquid the temperatures of the oscillator and its environment are equal while, in contrast, in a nonequilibrium glassy phase we find that $T_{\text{o}}$ substantially exceeds the bath temperature.