April 1, 2017 at 10:30 pm

Physics Colloquium | DNA Colloids: Crystals, Transformations, Building Blocks and Beyond, April 7

The Physics & Astronomy Colloquium Series presents John Crocker from Institute for Medicine and Engineering, Pennsylvania Muscle Institute, University of Pennsylvania on DNA Colloids:  Crystals, Transformations, Building Blocks and Beyond on Friday, April 7, at 4:10 p.m. in Walter 245.

John Crocker

John Crocker

Abstract: DNA is a versatile tool for directing the equilibrium self-assembly of nanoscopic and microscopic objects into interesting and useful three-dimensional structures. DNA induces highly controllable short-ranged attractive interactions between different particles, that can be measured directly using optical tweezers methods.  Recently, we successfully assembled DNA-grafted nanocolloids into a variety of unique binary colloidal crystal structures. To date, by varying the interactions between and among two particle species, we have observed three different binary crystal structures that homogeneously nucleate from the fluid, as well as multiple Martensitic transformations and lattice reconstructions that give rise to at least another 8 distinct crystals structures. We find that many of these structures are related to one another via a ‘family tree’ which manifests as a low-energy manifold in high-dimensional configuration space. In a separate study, we also generate a library of DNA-labeled colloidal building blocks by utilizing colloidal crystal templates and reprogrammable DNA interactions. The symmetry of the colloidal cluster building blocks is controlled by the symmetry of the crystal template and the location of ‘seed’ particles embedded within them. From close-packed colloidal crystals, we can generate five distinct cluster symmetries: cuboctahedra, triangular orthobicupola, icosahedra, octahedra, and tetrahedra. These clusters in turn possess directional interactions that can be used for hierarchical self-assembly of still more complex, ordered structures.

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