Colloidal ionic complexes on periodic substrates: ground state configurations and pattern switching

TL;DR

This paper explores the ordering, pattern formation, and switching behavior of colloidal ionic clusters on periodic substrates, revealing various stable configurations and the potential for external control of patterns.

Contribution

It provides a comprehensive theoretical and numerical analysis of colloidal cluster arrangements and pattern switching on optical trap arrays, identifying new stable supercomplexes and switching mechanisms.

Findings

Identification of stable cluster configurations including grape-like and rocket-like structures.

Observation of pattern transitions from rod-like to percolated structures as lattice spacing varies.

Demonstration of external electric fields enabling macroscopic pattern switching.

Abstract

We theoretically and numerically studied ordering of "colloidal ionic clusters" on periodic substrate potentials as those generated by optical trapping. Each cluster consists of three charged spherical colloids: two negatively and one positively charged. The substrate is a square or rectangular array of traps, each confining one such cluster. By varying the lattice constant from large to small, the observed clusters are first rod-like and form ferro- and antiferro-like phases, then they bend into a banana-like shape and finally condense into a percolated structure. Remarkably, in a broad parameter range between single-cluster and percolated structures, we have found stable supercomplexes composed of six colloids forming grape-like or rocket-like structures. We investigated the possibility of macroscopic pattern switching by applying external electrical fields.