Tuning Stoichiometry to Promote Formation of Binary Colloidal Superlattices

TL;DR

This study shows that excess small particles in binary colloidal mixtures promote the formation of stable superlattices by acting as plasticizers and disfavoring competing phases, as demonstrated through simulations and experiments.

Contribution

It reveals that an excess of smaller particles can be crucial for the self-assembly of binary colloidal superlattices, supported by simulation and experimental validation.

Findings

Excess small particles enable greater supersaturation before kinetic arrest.

They disfavor competing amorphous or metastable phases.

Simulation results closely match experimental observations.

Abstract

The self-assembly of binary nanoparticle superlattices from colloidal mixtures is a promising method for the fabrication of complex colloidal co-crystal structures. However, binary mixtures often form amorphous or metastable phases instead of the thermodynamically stable phase. Here we show that in binary mixtures of differently sized spherical particles, an excess of the smaller component can promote -- and, in some cases, may be necessary for -- the self-assembly of a binary co-crystal. Using computer simulations, we identify two mechanisms responsible for this phenomenon. First, excess small particles act like plasticizers and enable systems to reach a greater supersaturation before kinetic arrest occurs. Second, they can disfavor competing structures that may interfere with the growth of the target structure. We find the phase behavior of simulated mixtures of hard spheres closely matches published experimental results. We demonstrate the generality of our findings for mixtures of particles of arbitrary shape by presenting a binary mixture of hard shapes that only self-assembles with an excess of the smaller component. mixtures of particles of arbitrary shape by presenting a binary mixture of hard shapes that only self-assembles with an excess of the smaller component.