(650g) Thermodynamics and Kinetics of Phase Selection in Binary Colloidal Systems Mediated by DNA Interactions

Colloidal self-assembly provides a potential avenue for the design of novel devices with unique optical properties [1]. Colloidal systems also provide useful insights into fundamental mechanisms of phase transitions such as crystal nucleation [2], growth [3] and melting that are otherwise difficult to probe in atomic systems. In particular, micro- and nanoscale particles, functionalized with designer single-stranded DNA brushes, have now been successfully assembled into several crystalline phases, including ordered, binary superlattice structures.

While this early success is promising, further progress requires a rational approach for interaction design, especially if more interesting and useful structures are to be assembled. In this presentation, we apply a comprehensive ensemble of Monte Carlo simulations and free energy calculations to generate a detailed picture of assembly in binary colloidal systems mediated by DNA hybridization. An important aspect of the simulations is that the effective interaction potential produced by the DNA binding has been measured experimentally and modeled with high accuracy, thereby allowing for a close connection between simulation and experiments [4,5].

We show that a range of experimentally observed phenomena pertaining to the growth of binary crystals are explained well by the simulations [6]. In particular, we demonstrate that kinetic factors are important in not only determining the quality (i.e. compositional and morphological order) of a growing crystal, but also its phase. For binary systems in which unlike (?A-B?) interactions are dominant, both close-packed (rhcp) and non-close-packed (bcc, or CsCl) superlattice structures are feasible [7], but the competition between them is sensitively dependent on both thermodynamic and kinetic factors. The simulation framework presented here should be useful for finding optimal conditions and DNA designs for experimentally growing crystals with desired structures and low defect densities.

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[4] A.J. Kim, P.L. Biancaniello, and J.C. Crocker, Langmuir. 22, 1991 (2006)

[5] P.L. Biancaniello, A.J. Kim, and J.C. Crocker, Phys. Rev. Lett. 94, 058302 (2005)

[6] A.J. Kim, R.T. Scarlett, et al., Nature Materials 8, 52 (2009)

[7] S. Y. Park, et al., Nature 451, 553 (2008)