Self-assembly of Active Colloidal Molecules with Dynamic Function

TL;DR

This paper explores how catalytically active colloids can self-assemble into structures with dynamic functions, such as oscillations and run-and-tumble behavior, by leveraging non-equilibrium chemical interactions.

Contribution

It introduces a novel approach to designing self-assembled colloidal molecules with time-dependent functionalities inspired by proteins.

Findings

Colloidal molecules can exhibit spontaneous oscillations.

Colloidal structures can perform run-and-tumble dynamics.

Chemical gradients enable non-reciprocal interactions leading to complex behaviors.

Abstract

Catalytically active colloids maintain non-equilibrium conditions in which they produce and deplete chemicals and hence effectively act as sources and sinks of molecules. While individual colloids that are symmetrically coated do not exhibit any form of dynamical activity, the concentration fields resulting from their chemical activity decay as $1/r$ and produce gradients that attract or repel other colloids depending on their surface chemistry and ambient variables. This results in a non-equilibrium analogue of ionic systems, but with the remarkable novel feature of action-reaction symmetry breaking. We study solutions of such chemically active colloids in dilute conditions when they join up to form molecules via generalized ionic bonds, and discuss how we can achieve structures with time dependent functionality. In particular, we study a molecule that adopts a spontaneous oscillatory pattern of conformations, and another that exhibits a run-and-tumble dynamics similar to bacteria. Our study shows that catalytically active colloids could be used for designing self-assembled structures that posses dynamical functionalities that are determined by their prescribed 3D structures, a strategy that follows the design principle of proteins.