title: Bottom-Up Colloidal Crystal Assembly with a Twist.
abstract: Globally ordered colloidal crystal lattices have broad utility in a wide range of optical and catalytic devices, for example, as photonic band gap materials. However, the self-assembly of stereospecific structures is often confounded by polymorphism. Small free-energy differences often characterize ensembles of different structures, making it difficult to produce a single morphology at will. Current techniques to handle this problem adopt one of two approaches: that of the "top-down" or "bottom-up" methodology, whereby structures are engineered starting from the largest or smallest relevant length scales, respectively. However, recently, a third approach for directing high fidelity assembly of colloidal crystals has been suggested which relies on the introduction of polymer cosolutes into the crystal phase [Mahynski, N.; Panagiotopoulos, A. Z.; Meng, D.; Kumar, S. K. Nat. Commun. 2014, 5, 4472]. By tuning the polymer's morphology to interact uniquely with the void symmetry of a single desired crystal, the entropy loss associated with polymer confinement has been shown to strongly bias the formation of that phase. However, previously, this approach has only been demonstrated in the limiting case of close-packed crystals. Here, we show how this approach may be generalized and extended to complex open crystals, illustrating the utility of this "structure-directing agent" paradigm in engineering the nanoscale structure of ordered colloidal materials. The high degree of transferability of this paradigm's basic principles between relatively simple crystals and more complex ones suggests that this represents a valuable addition to presently known self-assembly techniques.
authors.affiliation: Chemical Informatics Research Group, Chemical Sciences Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899-8320, United States.
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Mahynski
authors.affiliation: Faculty of Physics, University of Vienna , Boltzmanngasse 5, A-1090 Vienna, Austria.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Rovigatti
authors.affiliation: Faculty of Physics, University of Vienna , Boltzmanngasse 5, A-1090 Vienna, Austria.
authors.forename: Christos N
authors.initials: CN
authors.lastname: Likos
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University , Princeton, New Jersey 08544, United States.
authors.forename: Athanassios Z
authors.initials: AZ
authors.lastname: Panagiotopoulos
keywords: colloidal crystals; colloids; crystal polymorphism; polymers; self-assembly; tetrastack