Nanotech 2010

Mass-Scale Shear-Directed NanoAssembly in Elastic Polymer Photonic Crystals

D.R.E. Snoswell, A. Kontogeorgos, J.J. Baumberg, T.D. Lord, M.R. Mackley, P. Spahn, G.P. Hellmann
University of Cambridge, UK

Keywords: colloid, photonic crystal, shear, self-assembly


Large-scale self-assembly of opals is achieved by shear-flow alignment of core-shell spheres in a polymer melt to produce aligned crystal samples tens of meters long, in which 10nm nanoparticles are also incorporated. Fabrication of the precursor spheres has been demonstrated in tonne quantities and their nanoassembly into opals has been achieved by standard extrusion and compression techniques to generate sheets, ribbons and fibres. Shear forces are crucial to the nanoassembly process of these rubber-like colloidal photonic crystals which display striking colour shifts on deformation. Nevertheless the shear-ordering and shear melting processes are challenging to study due to the high viscosity (~ 10,000 Pas) of this unique solvent-less system. By employing the use of a multipass rheometer, periods of crystal growth and decay in the highly viscous flowing polymer opal melts are monitored in-situ by spectroscopy of backscattered light from a broadband source. We thereby describe the mechanisms behind shear-induced assembly of polymer core-shell nanoparticles allowing optimal mass production of iridescent and elastic thin films with uniformly shear-aligned photonic crystals.
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