# Difference between revisions of "Many-Body Force and Mobility Measurements in Colloidal Systems"

Jason W. Merrill, Sunil K. Sainis, Jerzy Bławzdziewicz and Eric R. Dufresne

Soft Matter 6 (2010) p.2187-2192

wiki entry by Emily Russell, Fall 2010

The article can be found here.

## Overview

This paper introduces a technique whereby the mobility tensor of a system of particles can be determined from measurements of trajectories. Particles in close proximity can affect one another's mobility via hydrodynamic interactions through the medium, so that a force exerted on one particle indirectly causes motion of another as well. Thus the scalar mobility used in elementary fluid dynamics is not sufficient to describe the system; instead a mobility tensor is needed to take into account interactions between particles. The authors describe the calculation of this tensor in systems of three and seven particles, and find that it is well described by theoretical predictions.

## Experiments

The experiments performed use the same system as in a recent paper by three of the same authors, Many-Body Electrostatic Forces Between Colloidal Particles at Vanishing Ionic Strength: colloidal PMMA particles of 600 nm radius, in hexadecane with here 500 $\mu$M NaAOT surfactant to introduce charging of the particles. The particles were arranged using optical tweezers, and then released and trajectories recorded using a fast camera. This paper considers both an equilateral triangle of three particles, and a hexagonal arrangement of seven particles.

(entry in progress)