Forced motion of a probe particle near the colloidal glass 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 ${\varphi }_g$. For dense liquid-like samples near ${\varphi }_g$, 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 ${\varphi }_g$ 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.

7 pages, 4 figures revised version, accepted for publication in Europhysics Letters