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Abstract: Ligand oximation "converts' an hexametallic MnIII wheel into a dodecametallic MnIII wheel, while the magnetic exchange switches from ferro- to antiferromagnetic.

Open Access

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Abstract: We outline techniques for the control and measurement of the nucleation of crystalline material. SAXS/WAXS XRD measurements are presented that demonstrate the impact of low power, continuous, non-cavitational ultrasound on the nucleation and crystallisation of a wax; n-eicosane dissolved in heptane/toluene solvent. A mathematical-physical approach based on rectification of heat and mass transport by such a low power oscillating pressure field is outlined and it is suggested that this approach be combined with dissipative particle dynamics (DPD) computational modelling to develop a predictive method capable of modelling the impact of low power oscillating pressure fields (acoustics and ultrasonics) on a wide range of nucleating systems. Combining ultrasound pitch and catch speed of sound measurements with low power harmonically oscillating pressure fields to monitor and control nucleation presents the prospect of entirely new industrially significant methods of process control in crystallisation. It also offers new insights into nucleation processes in general. However, for the acoustic control technique to be applied widely, further theoretical and modelling work will be necessary since at present, we are unable to predict the precise effect of low power ultrasound in any given situation.

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Abstract: The combination of X-ray imaging and diffraction techniques provides a unique tool for structural and mechanical analysis of engineering components. A variety of modes can be employed in terms of the spatial resolution (length-scale), time resolution (frequency), and the nature of the physical quantity being interrogated. This thesis describes my contributions towards the development of novel X-ray “rich” imaging experimental techniques and data interpretation. The experimental findings have been validated via comparison with other experimental methods and numerical modelling. The combination of fast acquisition rate and high penetration properties of X-ray beams allows the collection of high-resolution 3-D tomographic data sets at submicron resolution during in situ deformation experiments. Digital Volume Correlation analysis tools developed in this study help understand crack propagation mechanisms in quasi-brittle materials and elasto-plastic deformation in co-sprayed composites. For the cases of crystalline specimens where the knowledge of “live” or residual elastic strain distributions is required, diffraction techniques have been advanced. Diffraction Strain Tomography (DST) allows non-destructive reconstruction of the 2-D (in-plane) variation of the out-of-plane strain component. Another diffraction modality dubbed Laue Orientation Tomography (LOT), a grain mapping approach has been proposed and developed based on the translate-rotate tomographic acquisition strategy. It allows the reconstruction of grain shape and orientation within polycrystalline samples, and provides information about intragranular lattice strain and distortion. The implications of this method have been thoroughly investigated. State-of-the-art engineering characterisation techniques evolve towards scrutinising submicron scale structural features and strain variation using the complementarity of X-ray imaging and diffraction. The first successful feasibility study is reported of in operando stress analysis in an internal combustion engine. Finally, further advancement of ‘rich’ imaging techniques is illustrated via the first successful application of Time-of-Flight Neutron Diffraction Strain (TOF-NDST) tomography for non-destructive reconstruction of the complete strain tensor using an inverse eigenstrain formulation.

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Abstract: In situ proteolysis is one of the most effective rescue strategies for protein crystallization, and optimization of the ratio between the protein and the protease is one of the key steps in the process. Seeding is a very powerful tool to optimize crystallization conditions and can be performed by most crystallization robots. Addition of protease instead of seed stock using a robot can be used to optimize the concentration of protease in in situ proteolysis experiments and has been successfully tested using two proteins.

Open Access

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Abstract: Hybrid halide perovskites have recently emerged as a highly efficient class of light absorbers; however, there are increasing concerns over their long-term stability. Recently, incorporation of SCN– has been suggested as a novel route to improving stability without negatively impacting performance. Intriguingly, despite crystallizing in a 2D layered structure, (CH3NH3)2Pb(SCN)2I2 (MAPSI) possesses an ideal band gap of 1.53 eV, close to that of the 3D connected champion hybrid perovskite absorber, CH3NH3PbI3 (MAPI). Here, we identify, using hybrid density functional theory, the origin of the smaller than expected band gap of MAPSI through a detailed comparison with the electronic structure of MAPI. Furthermore, assessment of the MAPSI structure reveals that it is thermodynamically stable with respect to phase separation, a likely source of the increased stability reported in experiment.