T2.1 Colloidal Crystals Engineered from Anisotropic Nanoparticles and DNA
Haixin Lin (Northwestern University)
DNA-mediated programmable assembly is a promising route for synthesizing novel materials. This strategy has been successfully used to synthesize crystalline structures with more than 35 different symmetries and over 500 structures. However, most of the properties of these colloidal crystals are dictated by the identity of the building blocks, instead of their structural arrangements. In contrast, crystal structure plays a crucial role in determining the properties of several traditional molecular/atomic crystals such as porous (e.g. MOFs, clathrates, zeolites) and anisotropic crystals (e.g. uniaxial crystals, biaxial crystals). Analogous porous or anisotropic colloidal crystals are difficult to fabricate given that the most commonly used building blocks are highly symmetric spherical particles. Unlike spherical particles, anisotropic particles can directionally guide the formation of DNA bonds with specific angles, which affects the lattice symmetry and crystal habit of the resulting colloidal crystals. In this work, we show two examples of how low symmetry nanoparticles assemble into either porous or anisotropic crystals.
Natural clathrates are mainly hydrate frameworks with a variety of host molecules such as methane. The cages in natural clathrates are formed when molecular or atomic nodes adopt discrete bond angles between 100 and 125°. To assemble the nanoparticle analog, oblate trigonal bipyramids were identified as ideal building blocks as they can promote the formation of DNA bonds with ~110° bond angle. DNA-mediated assembly of triangular bipyramids generated three different clathrate architectures, which, to date, are the most sophisticated architectures made by programmable assembly. The cavities in the clathrates may have potential for host-guest recognition applications (such as proteins or virus) as well as catalysis.
Natural anisotropic crystals have different refractive indices along different crystallographic axes which allows them to modulate the phase or path of light. Using low symmetry nanoparticles such as nanoscale pentabipyramids and nanorods, anisotropic colloidal crystals such as rhombohedra, hexagonal prisms, and rhombic prisms were assembled. In particular, colloidal rhombic prisms which have face-centered-orthorhombic symmetry, the lowest symmetry achieved by programmable assembly to date, were prepared. Importantly, these represent the first examples of biaxial colloidal crystals. Anisotropic colloidal crystals such as these have potential as important optical components in micro-optical systems.
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SYMPOSIUM T2 – MATERIALS PROCESSING AND CHEMISTRY
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Haixin Lin
Location: Technological Institute M177