Electrostatically Assembled Open Square and Checkerboard Superlattices

TL;DR

This paper presents a versatile method for assembling gold nanoparticles into various two-dimensional superlattices, including open square and checkerboard structures, by controlling interparticle interactions through polymer grafting and pH tuning.

Contribution

It introduces a unified approach to create diverse open superlattices at the liquid-air interface using pH-responsive polymer grafting on nanoparticles.

Findings

Polymer molecular weight controls superlattice symmetry.

pH tuning induces structural transitions between lattice types.

Method enables programmable fabrication of colloidal superstructures.

Abstract

Programmable assembly of nanoparticles into structures other than hexagonal lattices remains challenging. Assembling an open checkerboard or square lattice is harder to achieve compared to a close-packed hexagonal structure. Here, we introduce a unified, robust approach to assemble nanoparticles into a diverse family of two-dimensional superlattices at the liquid-air interface. Gold nanoparticles are grafted with pH-responsive, water-soluble poly(ethylene glycol) chains terminating in -COOH or -NH2 end groups, enabling control over interparticle interactions, while the grafted polymer's molecular weight dictates its conformation. This combined control crystallizes checkerboard, simple-square, and body-centered honeycomb superlattices. We find that even for identical nanoparticle core sizes, the polymer's molecular weight dictates superlattice symmetry and stability. Furthermore, tuning pH induces structural transitions between different lattice types. This method opens new avenues for the programmable fabrication of colloidal superstructures with tailored architectures.