Nucleation, Growth, and Transformations in DNA-Linked Binary Colloidal Superlattices

A promising approach for realizing versatile colloidal assembly is to graft single-stranded DNA oligomer brushes onto the surfaces of particles in order to create tunable attractive interactions between them.  Using this concept, micro- and nanoscale particles have now been successfully assembled into bulk crystalline phases, including a variety of ordered, binary superlattice structures.  However, there remain open questions regarding the prediction of nucleation and growth behavior in such structures as a function of DNA brush characteristics.  Moreover, recent observations of diffusionless transformations in binary colloidal crystallites further motivate a more mechanistic understanding of this class of materials. 

Here, we apply a combination of Monte Carlo simulations, Brownian dynamics simulations, and free energy calculations to generate a detailed picture for the assembly of binary colloidal superlattice crystals.  We first describe a pseudo-phase diagram that includes both thermodynamic and kinetic influences on homogeneously nucleated colloidal crystallites and demonstrate how kinetic limitations during crystal growth play a direct role in establishing the observed phase.  Next, we also present a detailed analysis of diffusionless transformations between body-centered and face-centered cubic configurations of binary colloidal crystals and demonstrate that hydrodynamic factors play an important role in establishing the final structure.