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.

The addition of a starch or gum-based thickener to patient fluids with dysphagia is commonly carried out, but the mechanism behind the efficacy of this treatment is not fully understood. This paper describes the rheological behavior of two commercially available thickening powders and an additional xanthan gum solution with a view to explaining the efficacy of thickened fluids in terms of their rheology. Both linear viscoelastic and steady shear data were obtained for the fluids together with filament extensional stretch, decay, and breakup data. In order to follow the behavior of the fluids in a processing situation, a mechanical "Cambridge Throat" was designed and tested. The action of the tongue was modeled using a constant torque cam that forced fluid contained within a flexible membrane through a model throat. Movie photography captured images of the fluid behavior and showed that for a constant tongue torque, the transit time within the model throat increased with increasing fluid viscosity, with implications for the time available for the successful function of the larynx, throat muscles, and epiglottis. V

This paper describes rheological measurements and associated optical microstructural observations of multiwall carbon nanotubes ͑MWCNTs͒ suspended in an epoxy resin matrix. The base epoxy resin was found to be essentially Newtonian, and the progressive incorporation of nanotubes enhanced the low shear rate viscosity of the suspension by nearly two decades. At higher shear rates, the suspension viscosity asymptotically thinned to the viscosity of the matrix alone. The low shear rate viscosity enhancement was correlated with the optical observations of interconnected aggregates of carbon nanotubes, which themselves were induced by the low shear conditions. Intermediate shear rates resulted in a reduction in the size of the aggregates. High shear rates appeared to cause near-complete dispersal of the aggregates. From these results it is conjectured that for this suspension, shear thinning is connected with the breaking of the interconnected networks between nanotubes and or aggregates of nanotubes, and not by nanotube alignment.

The atomic displacements of many of the atoms in a macromolecular structure can be modelled in terms of group motions described in the harmonic approximation by T, L and S tensors. Relevant groups may be planar side groups of protein chains, units of secondary structure such as o~-helices or whole protein domains. For the TLS parameters to be interpreted, they must be related to the axes of inertia of the rigid groups and, in the case of the T and S tensors, must be calculated with respect to the centre of reaction of the rigid group. A program (TLSANL)is described that analyses these 21 TLS rigid-body displacement parameters and their relation with the principal axes of the rigid body, from the output of the segmented anisotropic refinement of a macromolecular structure, as produced by a program such as RESTRAIN

Preliminary results are presented in which the interdiffusion coefficient for hydrogenated and deuterated polystyrene has been measured at 115°C in situ and in real time using neutron reflectivity (NR). The interfacial width shows a t 1/4 time dependence in the initial stages of diffusion which changes to t 1/2 at longer annealing times, from which a diffusion coefficient D ) (1.7 ( 0.2) × 10 -17 cm 2 s -1 is obtained. Similar in situ real-time NR methods have been used to measure the ingress of oligomeric styrene into high-molecular-weight polystyrene at 65°C. A highly asymmetric interfacial profile is seen which is qualitatively in agreement with theory.The early stages of interdiffusion at polymer interfaces has been studied by a number of techniques. 1-6 Neutron reflectivity (NR) has been shown to be ideally suited to these problems, 7-10 allowing the accurate determination of not only the width of the interface but also the interfacial profile between the interdiffusing polymers. The normal way of studying the diffusion process is to use an "anneal-quench" procedure where the sample is heated for a given time above the glasstransition temperatures (T g 's) of the polymers and then rapidly quenched to room temperature, after which a full reflection profile is collected. This procedure is repeated for each successive annealing time. Classical Fickian diffusion 11 has been shown to apply only at annealing times greater than the reptation time, τ r . Detailed NR studies of interdiffusion between polymers with similar molecular weights have shown that for times below τ r different power law time dependencies exist for the interfacial width. 7 In these cases, the interfacial profile can be described by symmetric functions, either error or hyperbolic tangent functions. When the polymer molecular weights are dissimilar, the interfacial shape becomes highly asymmetric 8,12,13 with a discontinuous interfacial profile that has components relating to the different diffusion rates of the two species. Although the anneal-quench procedure has proved very successful for amorphous polymer systems where the T g of both polymers are well above room temperature, it is not applicable for the study of systems where the T g for one or both polymers is close to or less than room temperature or if small-molecule ingress into a polymer layer is to be studied. Since the interface remains mobile at room temperature, an extremely rapid quench to below room temperature must be made where the diffusing species are immobilized for the length scale of the NR measurement. Difficulties may arise if either the quench is not rapid enough or the interface is disturbed by the quench process, which it undoubtedly will be when heating the sample for the next annealing.Another approach, which has only recently become possible with the advent of higher flux NR instruments, is in situ real-time reflectivity measurements. Such measurements have been attempted in the past using point-by-point θ-2θ fixed-wavelength NR measurements by taking a partial ref...