(458a) Prediction and Assembly of Binary, Ionic Colloidal Crystals

Colloidal materials are important both as a model system for atoms and molecules and as advanced engineering materials. Specifically, colloidal crystals have applications as sensors, band-gap materials, and scaffold structures 1,2. Systems of binary, ionic colloidal crystals have been shown, through both experimental and computational studies, to self-assembly into a variety of crystal structures -- dependent on particle size ratio and charge ratio, and screening length 3-5. We extend the predictions of ionic colloidal crystals by combining lattice energy calculations and normal mode analysis to produce a fast, effective method to screen potential crystal structures and predict theoretical phase diagrams. We use molecular dynamics simulations to validate and explore these phase diagrams. The method is of interest to the experimental realization of ionic colloidal crystals because it provides a rapid method to evaluate the possibility that particular combinations of colloidal pair potential parameters will yield particular kinds of ionic colloidal crystals. 1. Cui, Q., Muscatello, M. M. W. & Asher, S. A. Photonic crystal borax competitive binding carbohydrate sensing motif. ANALYST 134, 875-880 (2009). 2. Lee, Y. J. & Braun, P. V. Tunable inverse opal hydrogel pH sensors. ADVANCED MATERIALS 15, 563-566 (2003). 3. Bartlett, P. & Campbell, A. I. Three-dimensional binary superlattices of oppositely charged colloids. PHYSICAL REVIEW LETTERS 95, (2005). 4. Leunissen, M. E. et al. Ionic colloidal crystals of oppositely charged particles. NATURE 437, 235-240 (2005). 5. Maskaly, G. R., Garcia, R. E., Carter, W. C. & Chiang, Y. M. Ionic colloidal crystals: Ordered, multicomponent structures via controlled heterocoagulation. PHYSICAL REVIEW E 73, (2006).