An experimental and theoretical determination of oscillatory shear-induced crystallization processes in viscoelastic photonic crystal media

A study is presented of the oscillatory shear-ordering dynamics of viscoelastic photonic crystal media, using an optical shear cell. The hard-sphere/“sticky”-shell design of these polymeric composite particles produces athermal, quasi-solid rubbery media, with a characteristic viscoelastic ensemble response to applied shear. Monotonic crystallization processes, as directly measured by the photonic stopband transmission, are tracked as a function of strain amplitude, oscillation frequency, and temperature. A complementary generic spatio-temporal model is developed of crystallization due to shear-dependent interlayer viscosity, giving propagating crystalline fronts with increasing applied strain, and a gradual transition from interparticle disorder to order. The introduction of a competing shear-induced flow degradation process, dependent on the global shear rate, gives solutions with both amplitude and frequency dependence. The extracted crystallization timescales show parametric trends which are in good qualitative agreement with experimental observations

Spectroscopic Ellipsometry and Optical Modelling of Structurally Colored Opaline Thin-Films

The method of spectroscopic ellipsometry is applied to complex periodic nanomaterials, consisting of shear-ordered polymeric nanosphere composites, with intense resonant structural color. A corresponding multilayer optical quasi-model of the system, parametrizing the inherent degree of sample disorder and encompassing key properties of effective refractive-index and index-contrast, is developed to elucidate the correlation between the ∆ and Ψ ellipsometric parameters and the shear-induced opaline crystallinity. These approaches offer reliable means of in-line tracking of the sample quality of such “polymer opals” in large scale processing and applications

Transparent Polymer Opal Thin Films with Intense UV Structural Color

We report on shear-ordered polymer photonic crystals demonstrating intense structural color with a photonic bandgap at 270 nm. Our work examines this UV structural color, originating from a low refractive index contrast polymer composite system as a function of the viewing angle. We report extensive characterization of the angle-dependent nature of this color in the form of ‘scattering cones’, which showed strong reflectivity in the 275–315 nm range. The viewing range of the scattering was fully quantified for a number of planes and angles, and we additionally discuss the unique spectral anisotropy observed in these structures. Such films could serve as low-cost UV reflection coatings with applications in photovoltaics due to the fact of their non-photobleaching and robust mechanical behavior in addition to their favorable optical properties

Transparent Polymer Opal Thin Films with Intense UV Structural Color

We report on shear-ordered polymer photonic crystals demonstrating intense structural color with a photonic bandgap at 270 nm. Our work examines this UV structural color, originating from a low refractive index contrast polymer composite system as a function of the viewing angle. We report extensive characterization of the angle-dependent nature of this color in the form of ‘scattering cones’, which showed strong reflectivity in the 275–315 nm range. The viewing range of the scattering was fully quantified for a number of planes and angles, and we additionally discuss the unique spectral anisotropy observed in these structures. Such films could serve as low-cost UV reflection coatings with applications in photovoltaics due to the fact of their non-photobleaching and robust mechanical behavior in addition to their favorable optical properties

Nanoassembly of Polydisperse Photonic Crystals Based on Binary and Ternary Polymer Opal Alloys

Ordered binary and ternary photonic crystals, composed of different sized polymer-composite spheres with diameter ratios up to 120%, are generated using bending induced oscillatory shearing (BIOS). This viscoelastic system creates polydisperse equilibrium structures, producing mixed opaline colored films with greatly reduced requirements for particle monodispersity, and very different sphere size ratios, compared to other methods of nano-assembly

Anarchy in the UK('s most famous fortress): comradeship and cupidity in Gibraltar and neighbouring Spain, 1890-1902

This article is the first to investigate the growth of anarchist ideology and tactics in Gibraltar and the surrounding Spanish region, the Campo de Gibraltar, in the period 1890-1902. We draw upon hitherto unused material from both The National Archives in London and the Gibraltar Government Archives. By doing so, we demonstrate that during this period Gibraltarian and Spanish workers came together, not only to defend and advance their interests by direct action, such as strikes and attacks on employers, but also to advance educational and social causes too. Indeed, by 1898-9 the appeal of this movement was so strong that an attempt by the British Social Democratic Federation to establish a more constitutionalist approach to industrial relations failed. By 1902, the power of anarchist movements and tactics concerned employers in Gibraltar so greatly that they engineered a lock-out – styled a general strike by local workers – and successfully smashed the organising power of the local movement. Meanwhile, on the Spanish side of the frontier a massacre engineered by the local Spanish authorities resulted in the deaths of a number of activists and a hiatus in the movement that would last until the Great War of 1914-18

Large-scale ordering of nanoparticles using viscoelastic shear processing

This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Nature Publishing Group.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 (BIOS) technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong structural colour. With oscillatory strain amplitudes of 300%, crystallisation initiates at the wall and develops quickly across the bulk within only 5 oscillations yielding sharp intense reflectance peaks of tunable colour. The resulting structure of randomly stacked hexagonal close-packed layers parallel to the shear plane, 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 photonics materials, and forms a generic tool for ordering nanoparticles.We acknowledge EPSRC grants EP/G060649/1, EP/H027130/1, EP/E040241, EP/L027151/1 and EU ERC grants LINASS 320503 and FP7 291522-3DIMAGE