Many-Body Force and Mobility Measurements in Colloidal Systems

TL;DR

This paper introduces a method to measure forces and mobility tensors in colloidal systems by analyzing particle trajectories, revealing that mobility aligns with pairwise Stokeslet models while electrostatic interactions do not.

Contribution

The authors present a novel technique for simultaneous force and mobility measurements in colloids, applicable to complex 3D arrangements and non-spherical particles.

Findings

Mobility tensor fits pairwise Stokeslet model

Electrostatic interactions deviate from pairwise models

Technique is extendable to complex colloidal systems

Abstract

We demonstrate a technique for simultaneously measuring each component of the force vectors and mobility tensor of a small collection of colloidal particles based on observing a set of particle trajectories. For a few-body system of micron-sized polymer beads in oil separated by several particle radii, we find that the mobility tensor is well-described by a pairwise Stokeslet model. This stands in contrast to the electrostatic interactions, which were found to deviate significantly from a pairwise model. The measurement technique presented here should be simple to extend to systems of heterogeneous, non-spherical particles arranged in arbitrary 3D geometries.