Friction Boosted by Equilibrium Misalignment of Incommensurate Two-Dimensional Colloid Monolayers

TL;DR

This paper predicts that incommensurate colloid monolayers in an optical lattice naturally adopt a small misalignment angle in equilibrium, which significantly enhances friction during sliding, revealing a new mechanism affecting incommensurate interfaces.

Contribution

It introduces the novel prediction that equilibrium misalignment in incommensurate colloid monolayers boosts friction, supported by realistic simulations and experimental observations.

Findings

Equilibrium misalignment angle exists in incommensurate monolayers.

Misalignment significantly increases friction during sliding.

The effect may be common in other incommensurate adsorbed layers.

Abstract

Colloidal 2D monolayers sliding in an optical lattice are of recent importance as a frictional system. In the general case when the monolayer and optical lattices are incommensurate, we predict two important novelties, one in the static equilibrium structure, the other in the frictional behavior under sliding. Structurally, realistic simulations show that the colloid layer should possess in full equilibrium a small misalignment rotation angle relative to the optical lattice, an effect so far unnoticed but visible in some published experimental moir\'e patterns. Under sliding, this misalignment has the effect of boosting the colloid monolayer friction by a considerable factor over the hypothetical aligned case discussed so far. A frictional increase of similar origin must generally affect other incommensurate adsorbed monolayers and contacts, to be sought out case by case.