Active and Nonlinear Microrheology in Dense Colloidal Suspensions

TL;DR

This paper develops a first-principles theoretical framework for active nonlinear microrheology in dense colloidal suspensions, analyzing probe particle behavior under external forces and connecting theory with experiments and simulations.

Contribution

It introduces an exact expression for friction in active microrheology and explores the force threshold for probe delocalization within mode-coupling theory.

Findings

Derived an exact friction expression for active microrheology.

Identified the force threshold for probe delocalization.

Explained experimental and simulation data with a simplified model.

Abstract

We present a first-principles theory for the active nonlinear microrheology of colloidal model systems: for constant external force on a spherical probe particle embedded in a dense host dispersion, neglecting hydrodynamic interactions, we derive an exact expression for the friction. Within mode-coupling theory (MCT), we discuss the threshold external force needed to delocalize the probe from a host glass, and its relation to strong nonlinear velocity-force curves in a host fluid. Experimental microrheology data and simulations, which we performed, are explained with a simplified model.