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Item Restricted Modelling Crystallisation in Polymers(University of Sheffield, 2024-06-03) Algethami, Rasha; Clarke, NigelIn this thesis, we introduce the development of a computational model, combining a coarse-grained phase field approach with hydrodynamics using the Stokes equation under low Reynold's number conditions. This innovative model successfully elucidates the growth patterns of rhombus-shaped single crystals in polymers driven by chemical potential gradients and fluid flow. Unlike traditional methods, this study treats the single crystal as a highly viscous fluid, employing fluid-particle dynamics, thereby eliminating the need for intricate boundary conditions at the crystal-fluid interface. The investigation commences with the development of a finite difference-based phase field model, enabling the simulation of polymer crystal growth from a simple melt. The model adapts two thermodynamic driving forces to account for the meta-stable phases in crystallisation. This model allows for the exploration of diverse crystal morphologies, including circular, rectangular, and rhombus shapes. In depth analysis of isotropic and anisotropic interfacial energies reveals their significant influence on crystal growth rates and shapes. Moreover, the study extends to the interaction between adjacent single crystals, uncovering merging processes and growth rates under constant and non-constant interface mobility. A key aspect of this research lies in the validation of the model, performed within a simple shear flow system. This validation not only ensures the model's accuracy but also offers insights into the complicated relationship between fluid flow and crystal rotation. Through simulations, the study showed how different flow conditions impact polymer crystal rotation rates and patterns. Furthermore, the study delves into the role of interface thickness and interfacial energy on crystal motion and growth dynamics. By altering the interface thickness over time and maintaining it constant in other instances, the study reveals noticeable effects on crystal rotation and growth. The results show that crystal rotation increases significantly with changing interface thickness compared to the case where the interface thickness remains constant. However, the crystal growth exhibits a considerable increase where the interface thickness remains fixed. Additionally, variations in interfacial energy along different directions are shown to influence crystal rotation and growth rates significantly. The research also introduces a theoretical framework explaining crystal rotation driven by induced asymmetrical flow in a polymer melt. The theoretical predictions, when compared with computational simulations, are considered satisfactory, despite slight disparities attributed to specific assumptions.11 0Item Restricted Synthesis and Optimisation of Diopside Glass-Ceramics for Dentistry and Biomedical Applications.(Saudi Digital Library, 2023-12-20) Almusali, Mustafa Hassan E; Faris, TamaraAim: To synthesise new high strength Diopside glass-ceramics based on diopside solid solution system, that would be thermally compatible with yttria-stabilised zirconia polycrystalline (YTZP) substrates. This may address YTZP clinical failure rates, due to failure of the veneering material. Methods: A series of experimental glasses were designed using an Appen model and synthesised using melt quench methods. Glasses were then ball milled to achieve different particle sizes (<125 and <45 microns). The glasses were characterised using X-ray diffraction (XRD), dilatometry and differential scanning calorimetry (DSC) to find optimised nucleation curves. Two-step heat treatments were carried out for the glasses to make Diopside glass- ceramics. Glasses and Diopside glass-ceramics were characterised using secondary electron imaging (SEI), magic angle spinning nuclear magnetic resonance (MAS-NMR) and XRD. Optimised Diopside glass-ceramic (group 1) and IPS e.max Ceram (group 2) were veneered onto YTZP substrates to form bilayered specimen groups (n=30 per test group). The biaxial flexural strength (BFS) of the experimental Diopside glass-ceramics, IPS e.max Ceram ceramic and the bilayer specimen groups were tested using the ball on ring test at a crosshead speed of 1mm per minute. Results: XRD revealed that all glasses synthesised were amorphous, while glass-ceramics showed a major Diopside crystal phase and some formulations albite and wollastonite as minor phases. Dilatometry showed thermal expansion coefficients (CTE) ranging from 8.40-10.99 3 x10-6/k which was within the range thermally compatible with YTZP (10.86x10-6). DSC showed sharp nucleation peaks with little shift in crystallisation peaks for glasses at different particle size, suggesting bulk crystallisation. SEM of the glasses showed homogenously distributed spherical domains, while the glass-ceramic indicated dendritic, elongated diopside crystals and an interconnected unique microstructure with no microcracking present in the glassy matrix. MAS-NMR of 27Al of the diopside glass-ceramics showed two broad peaks, the major corresponding to tetrahedral aluminium (Al) and the other peak corresponding to octahedral aluminium (Al), which suggested the presence of a solid solution. Diopside glass-ceramics resulted in a high BFS (152.8 -196.7 MPa) which was significantly (p<0.05) higher compared to commercially available material IPS e.max Ceram (103.2 MPa). The BFS of experimental diopside glass-ceramic veneered onto YTZP showed high BFS (510.1MPa) which had a significantly higher (p<0.05) BFS when compared with IPS e.max Ceram veneered onto YTZP (324.7 MPa). Conclusions: A range of high strength (152.8 -196.7 MPa) diopside glass-ceramics were synthesised which were thermally compatible (8.40-10.99-x10-6/k) with YTZP. When veneered onto YTZP they produced a high BFS (510.1 MPa) that might help to reduce or preventing chipping failure rates encountered in veneered YTZP restorations.28 0