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Escobedo Research Group Published in Physical Review Letters and Featured in Soft Matter

Monday, November 24, 2014

The ability to create superlattices from two or more types of nanoparticles (“nanodots”) of different shapes and chemistries for any desirable composition is expected to open the door to novel applications, including active materials for photovoltaics, hybrid composites, and even photonic band gap materials. However, for nanoparticles of different shapes it is very difficult to form solid solutions due to the natural incompatibilities in the lattice structure of the pure components. Mihir Khadilkar, a Physics PhD student in Prof. Escobedo’s group, has now identified a robust rule to find the optimal relative particle size of the constituents so that they can co-assemble into binary crystals [1]. Via molecular simulations, the validity of such a rule has been demonstrated with several polyhedral particle shapes that individually form a plastic solid, and can form plastic binary solids for all compositions. The rule entails choosing particle sizes such that the expected osmotic pressure at the disorder-order transition for the pure components matches, and is physically rooted in the fact that at such conditions the efficiency with which each component packs space (related to the free volume per particle) is commensurate. Such an entropic match allows the components to achieve an ideal “marriage” in the solid state. This heuristic compatibilization rule was shown to be resilient to moderate polydispersity in size, to work with more than two components, and to lead to maximal “partial” solid-state miscibility in cases when particles differ widely in shape and type of structural order.

Also, a review by Prof. Escobedo on the general topic on entropy-aided self-assembly was recently published and chosen for the inside front cover of the journal Soft Matter [2].

[1] M. Khadilkar and F. A. Escobedo, “Heuristic rule for binary superlattice coassembly: Mixed plastic mesophases of hard polyhedral nanoparticles”, Phys. Rev. Lett. 113, 165504 (2014).

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[2] F. A. Escobedo, “Engineering entropy in soft matter: The bad, the ugly and the good”, Soft Matter 42, 8379 (2014).

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