Abstract
Over the last decade, the field of programmable self-assembly has seen an
explosion in the diversity of crystal lattices that can be synthesized from
DNA-coated colloidal nanometer- and micrometer-scale particles. The prevailing
wisdom has been that a particular crystal structure can be targeted by
designing the DNA-mediated interactions, to enforce binding between specific
particle pairs, and the particle diameters, to control the packing of the
various species. In this article, we show that other ubiquitous nonspecific
interactions can play equally important roles in determining the relative
stability of different crystal polymorphs and therefore what crystal structure
is most likely to form in an experiment. For a binary mixture of same-sized
DNA-coated colloidal micrometer-scale particles, we show how changing the
magnitudes of nonspecific steric and van der Waals interactions gives rise to a
family of binary body-centered tetragonal crystals, including both
cesium-chloride and copper-gold crystals. Simulations using pair potentials
that account for these interactions reproduce our experimental observations
quantitatively, and a theoretical model reveals how a subtle balance between
specific and nonspecific forces determines the equilibrium crystal structure.
These results highlight the importance of accounting for nonspecific
interactions in the crystal-engineering design process.