Packing Polydisperse Colloids into Crystals: When Charge-Dispersity Matters

Monte Carlo simulations, fully constrained by experimental parameters, are found to agree well with a measured phase diagram of aqueous dispersions of nanoparticles with a moderate size polydispersity over a broad range of salt concentrations, c(s), and volume fractions, phi. Upon increasing phi, the colloids freeze first into coexisting compact solids then into a body centered cubic phase (bcc) before they melt into a glass forming liquid. The surprising stability of the bcc solid at high phi and c(s) is explained by the interaction (charge) polydispersity and vibrational entropy.