Finlayson, C. E., Spahn, P., Snoswell, D. R. E., Yates, G., Kontogeorgos, A., Haines, A. I., Hellmann, G. P., Baumberg, J. J. (2011). 3D Bulk Ordering in Macroscopic Solid Opaline Films by Edge-Induced Rotational Shearing. Advanced Materials, 23 (13), pp. 1540-1544.A breakthrough in the field of large area photonic structures is reported, based on permanent ordering of solid polymeric films of sub-micrometer spheres by edge rotational-shearing. The resulting high-quality polymer opal thin-films exhibit strikingly intense structural color, as confirmed by combining a number of spectroscopic approaches. This induced self-assembly on macroscopic length scales represents a step-change away from current surface lithographies, presenting new routes for assembling solid ordered photonic materials. Despite previous reports of shear-ordering in sedimentary colloids in solution, no precedents exist for the application of such techniques to these granular solvent-free systems, which allow formation of permanent composite structures in the solid-state.Peer reviewe

Despite the availability of elaborate varieties of nanoparticles, their assembly into regular superstructures and photonic materials remains challenging. Here we show how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour. With oscillatory strain amplitudes of 300%, crystallization initiates at the wall and develops quickly across the bulk within only five oscillations. The resulting structure of random hexagonal close-packed layers is improved by shearing bidirectionally, alternating between two in-plane directions. Our theoretical framework indicates how the reduction in shear viscosity with increasing order of each layer accounts for these results, even when diffusion is totally absent. This general principle of shear ordering in viscoelastic media opens the way to manufacturable photonic materials, and forms a generic tool for ordering nanoparticles.

This article investigates the formation of nanostructured single crystals of calcite using direct, ion‐by‐ion precipitation methods and shows that single crystals with complex morphologies and curved surfaces can readily be formed using this technique. Calcite crystals with inverse opal and direct opal structures are prepared using templates of colloidal crystals and polystyrene reverse opals, respectively, and excellent replication of the template structures are achieved, including the formation of 200‐nm spheres of calcite in the direct opal structure. These highly porous crystals also display extremely regular, crystalline gross morphologies. The methodology is extremely versatile and challenges the preconception that nanostructured crystals cannot be prepared by simple diffusion of reagents into the template due to blocking of the channels. The results are also discussed in light of alternative templating methods using amorphous calcium carbonate (ACC) as a precursor phase and provide insight into the role of ACC in biological calcification processes.

We demonstrate the production of high-quality polymer opal fibers in an industrially-scalable process. These fibers exhibit structural color, based on the self-assembly of sub-micron core-shell particles, with a spectrum which is stretch-tunable across the visible region. The internal substructure and ordering of fibers, as inferred from variations in spectral bandwidth, is studied using dark-field microscopy. We employ a granular model to examine flow and shear forces during the extrusion process, and the effects on particle ordering. In both theory and experiment, a concentric zone of the fiber near the exposed surface develops particularly strong structural color. Such elastically-tuned structurally colored fibers are of interest for many applications.

We use elastically induced phase transitions to break the structural symmetry of self-assembled nanostructures, producing significantly modified functional properties. Stretching ordered polymer opals in different directions transforms the fcc photonic crystal into correspondingly distorted monoclinic lattices. This breaks the conventional selection rules for scattering from the crystal planes, yielding extra multiply scattered colors when the phase-breaking stretch is in specific directions. Scattering is spectroscopically tracked in real time as the samples distort, revealing a new phase transition that appears for <121>-oriented deformations.

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Spahn, P., Finlayson, C. E., Etah, W. M., Snoswell, D. R. E., Baumberg, J. J., Hellmann, G. P. (2011). Modification of the refractive-index contrast in polymer opal films. Journal of materials chemistry, 21 (24), 8893-8897.Synthetic opals, based on self-assembled arrays of core-shell (bead/matrix) polymer microspheres, are a promising platform for next-generation photonic structures, coatings and sensors. The refractive index contrast (Delta n) between beads and the matrix polymer is essential for the appearance of structural colour in polymer opal films. We report how the index contrast can be modified by engineering the chemical composition of the core-interlayer-shell (CIS) precursor particles. Alternative approaches to emulsion polymerisation, using the fluorinated monomer 2,2,2-trifluoroethyl acrylate and the aromatic monomer benzyl acrylate, yield a much larger range of Delta n values than for standard systems made from styrene and ethyl acrylate. Spectroscopic studies reveal striking differences in the transmission properties of thin-films as Delta n is varied from 0.045 up to 0.18.Peer reviewe

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