Forced motion of a probe particle near the colloidal glass transition

TL;DR

This study investigates the nonlinear motion of a magnetic probe in dense colloidal suspensions near the glass transition, revealing a force threshold for motion and volume fraction-dependent nonlinear drag.

Contribution

It provides experimental insights into the force-velocity relationship of a probe near the colloidal glass transition, highlighting the nonlinear dynamics close to the transition point.

Findings

Below threshold force, probe exhibits localized caged motion.

Above threshold, probe moves with fluctuating velocity.

Nonlinear force-velocity relationship intensifies near the transition.

Abstract

We use confocal microscopy to study the motion of a magnetic bead in a dense colloidal suspension, near the colloidal glass transition volume fraction $\phi_g$. For dense liquid-like samples near $\phi_g$, below a threshold force the magnetic bead exhibits only localized caged motion. Above this force, the bead is pulled with a fluctuating velocity. The relationship between force and velocity becomes increasingly nonlinear as $\phi_g$ is approached. The threshold force and nonlinear drag force vary strongly with the volume fraction, while the velocity fluctuations do not change near the transition.