Active Atoms and Interstitials in Two-dimensional Colloidal Crystals

TL;DR

This study investigates the dynamics of active particles in 2D colloidal crystals, revealing distinct behaviors as interstitials or atoms, and highlights their potential for creating non-close-packed active phases.

Contribution

It introduces experimental and numerical analysis of active particle motion in colloidal crystals, identifying new active behaviors and mechanisms at fluid interfaces.

Findings

Active interstitials perform run-and-tumble motion.

Active atoms exhibit intermittent motion influenced by the crystal landscape.

Results provide insights into dense active phases and non-close-packed crystalline structures.

Abstract

We study experimentally and numerically the motion of a self-phoretic active particle in two-dimensional (2D) loosely-packed colloidal crystals at fluid interfaces. Two scenarios emerge depending on the interaction between the active particle and the lattice: the active particle either navigates throughout the crystal as an interstitial or is part of the lattice and behaves as an active atom. Active interstitials undergo a run-and-tumble motion, with the passive colloids of the crystal acting as tumbling sites. Instead, active atoms exhibit an intermittent motion, which stems from the interplay between the periodic potential landscape of the passive crystal and the particle's self-propulsion. Our results shed new light on the behaviour of dense active phases and constitute the first step towards the realization of non-close-packed crystalline phases with internal activity.