Correlations in suspensions confined between viscoelastic surfaces: Noncontact microrheology

TL;DR

This paper presents a theoretical study of velocity cross-correlations in a viscous fluid confined by viscoelastic surfaces, proposing a noncontact microrheology method to measure viscoelastic properties without embedding tracers.

Contribution

It introduces a novel noncontact microrheology technique based on long-ranged correlations induced by boundary compliance, avoiding the need for tracer particles.

Findings

Velocity cross-correlations decay as 1/r with distance.

The method can extract viscoelastic properties without embedded tracers.

Robustness of the technique against confinement details.

Abstract

We study theoretically the velocity cross-correlations of a viscous fluid confined in a slit between two viscoelastic media. We analyze the effect of these correlations on the motions of particles suspended in the fluid. The compliance of the confining boundaries gives rise to a long-ranged pair correlation, decaying only as $1/r$ with the interparticle distance $r$. We show how this long-ranged effect may be used to extract the viscoelastic properties of the confining media without embedding tracer particles in them. We discuss the remarkable robustness of such a potential technique with respect to details of the confinement, and its expected statistical advantages over standard two-point microrheology.