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Dr Asaph Widmer-Cooper


Contact Details

ARC Australian Postdoctoral Fellow
Room 316
School of Chemistry, Building F11
The University of Sydney, NSW, 2006, Australia
E: asaph.widmer-cooper@sydney.edu.au
T: +61-2-9351-7392
F: +61-2-9351-3329

Career Profile

  • BSc (Hons I & Medal), University of Sydney, 1999
  • DAAD Fellow, German National Research Center for Information Science, 2000-2001
  • PhD, University of Sydney, 2006
  • Research Associate, University of Sydney, 2007
  • Postdoctoral Fellow, University of California at Berkeley and Lawrence Berkeley National Laboratory, 2008-2010
  • ARC Australian Postdoctoral Fellow, 2010-

Areas of Interest

  • Self-assembly of nanorods and nano-polyhedra
  • New materials for plasmonics and solar energy harvesting
  • Glass-formation, nucleation and crystal growth
  • Structure and dynamics of soft condensed matter
  • Statistical mechanics
  • Monte Carlo and molecular dynamics simulation

Research

My research focuses on understanding the behavior of complex fluids from a microscopic perspective using the tools of statistical mechanics and computer simulation. The questions I am interested in range from the fundamental, e.g. how do viscous liquids flow, to the applied, e.g. how to make nanocrystals assemble into structures that will be useful for harnessing solar energy. Common themes are a fascination with beautiful structures that can appear spontaneously in systems driven by disorder, and materials that have both liquid-like and solid-like properties. To inspire this work and to stimulate research on real physical systems I like to work closely with experimentalists. Among my current interests are the following:


Assembly of non-spherical nanoparticles for plasmonic and solar energy applications

Nanoparticles can now be made in an incredible array of materials, sizes, shapes, and patterns, often with unusual and tunable optical and electronic properties. Organizing such particles into extended structures that could revolutionize technology is a frontier area with a potential complexity rivaling that of molecular and organometallic self-assembly. I am working on two projects in this area which involve characterizing the interactions that exist between nanoparticles and between nanoparticles and various interfaces (fluid-solid, fluid-fluid) as well as their phase behavior and non-equilibrium dynamics: the first concerns the self-assembly of silver nano-polyhedra into mm-sized plasmonic supercrystals, where we have recently discovered and explained the formation of a new packing of octahedra with complex helical motifs (see image); and the second involves directing the assembly of semiconducting nanorods into nano-carpets that can be used for printing solar cells or, when combined with catalysts and embedded in a polymer membrane, for splitting water into hydrogen and oxygen.

How do viscous liquids flow?

When a liquid is cooled sufficiently fast, it will flow slower and slower until eventually it becomes a solid that lacks long-range crystalline order. This gradual glass transition is at the heart of how optical fibres are formed, super-elastic metals are made, and the rewritable CD functions. Understanding how and why this process occurs, however, is a fundamental problem that has puzzled scientists for over 100 years. We have shown that while glass-forming liquids lack long-range order they nevertheless have long-lived local and medium-range order that can influence their dynamic properties in complex ways. I am working to understand the relationship between chemical structure and dynamics in these liquids, how this influences the mechanism by which they relax internal and applied stresses, and the consequences this has for their mechanical properties.

Publications (2008 - 2013)

(cf. ResearcherID: E-6923-2010)

  1. Colombo, J; Widmer-Cooper, A and Del Gado, E. Microscopic picture of cooperative processes in restructuring gel networks. Physical Review Letters, 110 (19), 198301, 2013. DOI: 10.1103/physrevlett.110.198301

  2. Lenzen, M; Dey, C; Foran, B; Widmer-Cooper, A; Ohlemüller, R; Williams, M and Wiedmann, T. Modelling interactions between economic activity, greenhouse gas emissions, biodiversity and agricultural production. Environmental Modeling and Assessment, published online, 2013. DOI: 10.1007/s10666-012-9341-3

  3. Henzie, J; Grünwald, M; Widmer-Cooper, A; Geissler, PL and Yang, P. Self-assembly of uniform polyhedral silver nanocrystals into densest packings and exotic superlattices. Nature Materials, 11 (2), 131-137, 2012. DOI: 10.1038/NMAT3178

  4. Widmer-Cooper, A and Harrowell, P. Structural phases in non-additive soft-disk mixtures: Glasses, substitutional order, and random tilings. The Journal of Chemical Physics, 135, 224515, 2011. DOI: 10.1063/1.3666010

  5. Henzie, J; Grünwald, M; Widmer-Cooper, A; Geissler, PL and Yang, P. Self-assembly of uniform polyhedral silver nanocrystals into densest packings and exotic superlattices. Nature Materials, 1-7, 2011. DOI: 10.1038/nmat3178

  6. Candelier, R; Widmer-Cooper, A; Kummerfeld, JK; Dauchot, O; Biroli, G; Harrowell, P and Reichman, DR. Spatiotemporal hierarchy of relaxation events, dynamical heterogeneities, and structural reorganization in a supercooled liquid. Physical Review Letters, 105 (13), 135702 (pp 1-4), 2010. DOI: 10.1103/PhysRevLett.105.135702

  7. Baker, JL; Widmer-Cooper, A; Toney, M; Geissler, P and Alivisatos, AP. Device-scale perpendicular alignment of colloidal nanorods, Nano Lett. 10 (1), 195-201, 2010. DOI: 10.1021/nl903187v

  8. Widmer-Cooper, A; Perry, H; Harrowell, P and Reichman, DR. Localized soft modes and the supercooled liquid’s irreversible passage through its configuration space. The Journal of Chemical Physics, 131 (19), 194508 (12 pages), 2009. DOI: 10.1063/1.3265983

  9. Widmer-Cooper, A and Harrowell, P. Central role of thermal collective strain in the relaxation of structure in a supercooled liquid. Physical Review E, 80 (6), 061501 (6 pages), 2009. DOI: 10.1103/PhysRevE.80.061501

  10. Lenzen, M; Lane, A; Widmer-Cooper, A and Williams, M. Effects of Land Use on Threatened Species. Conserv. Biol. 23 (2), 294-306, 2009. DOI: 10.1111/j.1523-1739.2008.01126.

  11. Widmer-Cooper, A; Perry, H; Harrowell, P and Reichman, DR. Irreversible reorganization in a supercooled liquid originates from localized soft modes. Nature Physics, 4 (9), 711-715, 2008.DOI: 10.1038/nphys1025