Large-scale ordering of nanoparticles using viscoelastic shear processing

Abstract

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.

Functional Polymer Opals and Porous Materials by Shear‐Induced Assembly of Tailor‐Made Particles

“…In general, significant efforts have been undertaken in order to improve the macroscopic arrangement of colloidal spheres into an ordered 3D structure. Compared to the above mentioned techniques, the so‐called melt‐shear organization of core/shell particles provides access to photonic crystal films on the industrial length‐scale . The basic concept and major advantages were reported by the Hellmann group .…”

“…Large‐area self‐supporting photonic crystal films could be obtained . As a highlight, the bending‐induced oscillatory shear (BIOS) technique for core/shell particles could be used to further improve the large‐scale assembly . In the corresponding study, the Baumberg group and co‐workers elucidated the microscopic mechanisms behind crystallization and rheology of this unique system.…”

Tuning of Structural Colors Like a Chameleon Enabled by Shape‐Memory Polymers

“…The embedded PO spheres are poorly ordered at this stage, and the tape uncolored. A subsequent ordering step aligns the PO spheres to a regular lattice . This ordering is either performed by shearing the composite over a hot edge after the material is compressed into a film between two polyethylene terephthalate (PET) sheets, or by compressing the composite at high temperatures between two smooth plates in a hot embossing machine .…”

Highly Crystallized Brilliant Polymeric Photonic Crystals via Repulsion‐Induced Precipitation Assembly toward Multiresponsive Colorimetric Films

“…Apart from the above‐mentioned strategies, significant progress has been made in this area recently. For instance, an efficient and easy‐scalable route to self‐supporting elastomeric opal films with excellent optical properties has been developed by Schäfer and co‐workers . Based on a melt‐shear organization technology, this method can easily yield fully reversible large‐area multiresponsive 3D polymeric PC films by employing the special latex spheres with crosslinked core and a rubbery shell.…”