Stability of the binary colloidal crystalsAB2andAB13

Suspensions of binary mixtures of hard-sphere poly-methylmethacrylate colloidal particles were studied at six different size ratios $\alpha$. The main aim was to determine the range of size ratios over which the binary colloidal crystals $A{B}_2$ and $A{B}_{13}$ are stable. Combining these results with those of earlier work, we found stability of $A{B}_2$ for $0.60\gtrsim \alpha \gtrsim 0.425$, in good agreement with theoretical predictions by computer simulation and cell model methods. $A{B}_{13}$ was observed for $0.62\gtrsim \alpha \gtrsim 0.485$, the lower limit being significantly smaller than the theoretical prediction of about 0.525. Rough measurements of crystallization rates showed that $A{B}_2$ tended to crystallize fastest at small size ratios, whereas the opposite was true for $A{B}_{13}$. These findings should provide a guide to the optimum conditions for materials applications of these binary colloidal crystals.