New Light on Like-Charge Attraction

TL;DR

This paper investigates the pair interactions in charged colloidal systems, revealing that optical image distortions can create artifacts that mimic long-range attractions, thus clarifying previous experimental ambiguities.

Contribution

It identifies optical image distortions as a source of false long-range attraction signals in colloidal pair potential measurements.

Findings

Optical distortions can mimic long-range attractions in colloidal systems.

Distortions are significant at very small particle distances.

Correcting for distortions is essential for accurate pair potential measurements.

Abstract

We report on pair interaction measurements in charged colloidal systems in confined and unconfined geometries by means of optical microscopy. At very small particle distances we observe minute distortions in the optical images which can lead to artifacts in the pair potentials as derived by digital video microscopy. In particular, these distortions can pretend long-range attractions observed in charged colloidal suspensions.