Shape and Interaction Decoupling for Colloidal Pre-Assembly

TL;DR

This study demonstrates that colloidal cube-like particles can be pre-assembled into clusters with structure independent of particle shape and interaction type, enabling hierarchical material design through geometric and interaction decoupling.

Contribution

The paper introduces a method for geometric and interaction decoupling in colloidal pre-assembly, facilitating hierarchical structure formation with anisotropic particles.

Findings

Clusters of up to nine particles pack like spheres despite shape anisotropy.

Cluster structures are consistent across different inter-particle interactions.

Pre-assembled clusters can self-assemble into complex hierarchical structures.

Abstract

Creating materials with structure that is independently controllable at a range of scales requires breaking naturally occurring hierarchies. Breaking these hierarchies can be achieved via the decoupling of building block attributes from structure during assembly. Here, we demonstrate both geometric and interaction decoupling in pre-assembled colloidal structures of cube-like particles with rounded edges. Through computer simulations and experiments, we show that compressing a small number of such cubes in spherical confinement results in clusters with highly reproducible structures that can be used as mesoscale building blocks to form the next level of structural hierarchy. These clusters demonstrate geometric decoupling between particle shape and cluster structure; namely, for clusters of up to nine particles, the colloidal superballs pack consistently like spheres, despite the presence of shape anisotropy and facets in the cubic-like particles. We confirm that cluster structure is also decoupled from inter-particle interaction, showing that the same structures arise from the spherical confinement of both non-magnetic and magnetic colloidal cubes with strong dipolar interactions. To highlight the potential of these superball clusters for hierarchical assembly, we demonstrate, using computer simulations, that clusters of six to nine particles can self-assemble into high-order structures that differ from those of similarly shaped particles without pre-assembly. These results demonstrate decoupling for anisotropic building blocks that can be further exploited for hierarchical materials development.