(471e) Using Stoichiometry to Enhance Binary Colloidal Assembly

Self-assembly in binary colloidal mixtures has enabled the fabrication of colloidal superlattices with diverse structures. However, compared to single-component systems, binary mixtures are more likely subject to kinetic constraints like the formation of glasses or metastable phases, so understanding the best conditions for self-assembly is important. Here we computationally investigate the influence of stoichiometry on self-assembly, finding that an excess of the smaller component of a mixture relative to the stoichiometry of the superlattice can enhance its propensity for self-assembly. This contradicts the common assumption that self-assembly occurs best from a mixture at the same stoichiometry as the superlattice. For two systems we investigate, self-assembly can only be accomplished in the presence of excess small particles. We focus in particular on a system of repulsively soft spheres whose interparticle interaction closely resembles experiments with nearly hard spheres, finding strong agreement between simulation and previously conducted experiments. In general, we attribute the enhancement to increased particle mobility and disfavoring of possible competing phases. Our work provides a new way to overcome kinetic limitations and achieve binary self-assembly.