Bound Pairs: Direct Evidence for Long-range Attraction between Like-Charged Colloids

TL;DR

This study provides direct experimental evidence of long-range attraction between like-charged colloids, challenging traditional electrostatic repulsion models and revealing new insights into colloidal interactions.

Contribution

The paper presents the first direct observation of long-range attraction between like-charged colloids using confocal microscopy and detailed analysis of pair potentials.

Findings

Long-range attractive component in pair potential U(r)

Well depths of attraction exceed thermal energy

Stable bound pairs observed in dilute suspensions

Abstract

We report observations of stable bound pairs in very dilute deionized aqueous suspensions of highly charged polystyrene colloidal particles, with monovalent counterions, using a confocal laser scanning microscope. Through an analysis of several thousands of time series of confocal images recorded deep inside the bulk suspension, we find that the measured pair-potential, U(r) has a long-range attractive component with well depths larger than the thermal energy. These observations provide a direct and unequivocal evidence for the existence of long-range attraction in U(r) of like-charged colloidal particles.