Long-ranged attraction between disordered heterogeneous surfaces

TL;DR

This study challenges the conventional explanation for long-range attractions between charged surfaces in water, showing that inherent interaction asymmetry, not charge correlation, causes these forces.

Contribution

It demonstrates that long-range attractions are due to interaction asymmetry between charge domains, not charge correlation, based on direct force measurements under shear.

Findings

Long-range attraction occurs without charge correlation.

Interaction asymmetry explains the attraction.

Charge domain interactions are inherently asymmetric.

Abstract

Long-ranged attractions across water between two surfaces that are randomly covered with (mobile) positive and negative charge domains have been attributed to induced correlation of the charges (positive lining up with negative) as the surfaces approach. Here we show, by directly measuring normal forces under a rapid shear field, that these attractions may not in fact be due to such correlations. It is rather the inherent interaction-asymmetry between equally- and between oppositely-charged domains that results in the long-ranged attraction even in the complete absence of any charge correlation.