Saudi Cultural Missions Theses & Dissertations
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Item Restricted PROCESSING AND CHARACTERIZATION OF NYLON-12 PRODUCED BY SELECTIVE LASER SINTERING (SLS 3D PRINTING)(Lehigh University, 2022-05-06) Alghamdi, Naif Ahmed; Pearson, RaymondOver the last decade, nanocomposite materials have been widely used in the scientific literature to provide significant properties and improvements. Polyamide 12 is a familiar material for additive applications because of its manufacturability, such as in 3D printing. PA12 is known for its significant properties, such as extreme toughness, impact strength, abrasion resistance, good chemical resistance, good electrical insulation, and lightweight; as well as lower moisture absorption, lower melting point, and lower density compared to standard Nylons. This work will introduce and investigates three different commercial PA12 powders (Sintertac, Formlabs, and Sinterit) for Selective Laser Sintering. All three PA12 powders were examined by characterizing their chemical, mechanical, physical, and processing behavior. Several instruments, experiments, and studies were conducted to characterize the PA12 powders using several techniques such as Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Tapped density, and Hybrid Rheometer (DHR2, TA Instruments). However, PA12 powders were processed through a Selective Laser Sintering SLS 3D printer to print out ASTM D638-14 Type V specimens. Moreover, a Universal Testing Machine (UTS Instron 5567) to examine the 3D printed specimens19 0Item Restricted Polymeric Ionic Liquid Supported Catalysts Incorporating Polyoxometalate and/or Metal Nanoparticles(Newcastle University, 2024-04-18) Alrubayyi, Aeshah; Errington, JohnMetal nanoparticles have a significant interest because of their applications in catalysis and nanoscience, and their synthesis requires stabilisers to prevent nanoparticle aggregation. Metal nanoparticles can be stabilised by ionic liquids. Polymer ionic liquids have recently attracted attention. Doherty and Knight group has developed and utilized them as support to immobilize polyoxometalates, which were Keggin-type polyoxometalates [XM12O40]n- and Lindqvist type- polyoxometalates [M6O19]n- that Errington group designed and developed, and nanoparticles, and explored their applications. The stabilisation of metal nanoparticles such as Pd, Pt, Ag, Au, Ir, Rh, and Ru by polyoxometalates has been investigated by Weinstock and Papaconstintinou. This represents that polyoxometalate provides redox and Brønsted acid functionally that stabilised Metal nanoparticles, which are applied in chemical synthesis electrochemistry and photocatalysis. This project aimed to investigate the interface between the metal nanoparticles and polyoxometalates. A convenient reduction method by hydrazine was used to synthesize polyoxometalate-stabilised Auᵒ nanoparticles by forming electron-rich polyoxometalates by adding multiple electrons to the fully oxidized polyoxometalates, which increases the electron density. Reduced polyoxometalates can act as stabilisers and reducing agents to synthesize polyoxometalates-stabilised Au° nanoparticles. Chapter 1 briefly discusses the history of the development of polyoxometalates, the structure of polyoxometalates, and their application. Developing ionic liquids and utilizing polymer ionic liquids as support are introduced based on previous research and discussed. The second chapter describes the synthesis and characterization of polyionic liquid immobilised Au° nanoparticles and a hybrid catalyst incorporating Au° nanoparticles and polyoxometalates. The polystyrene-based immobilised ionic liquid was prepared via free radical polymerization and used to support Au° nanoparticles (PIIL@AuNP) and incorporate phosphotungstates H3PW12O40 (PIIL@AuNP-PW12). Various techniques, including thermogravimetric analysis (TGA), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM), have used to characterize all the prepared catalysts. The third chapter presents the results of the systematic evaluation of the efficacy of the newly prepared PIIL@AuNP and PIIL@AuNP-PW12 systems as catalysts for the selective reduction of nitrobenzene. PIIL@AuNP efficient catalysts in a 1:1 mixture of water and ethanol as the solvent for reduction of nitrobenzene to N-arylhydroxylamine, azoxybenzene, or aniline and incorporation of H3PW12O40 into PIIL@AuNP-PW12 switches the selectivity from N-arylhydroxylamine to aniline. This might be ascribed to the synergic creation of Brønsted acid sites in the presence of polyoxometalates. Chapter 4 describes the multi-electron reduction of phosphomolybdate (H3PMo12O40 and (TBA)3[PMo12O40]) and phosphotungstates (H3PW12O40 and (TBA)3[PW12O40]) and the interactions between the reduced anions and metal nanoparticles in an aqueous, non-aqueous and solid state. Transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), and 31P NMR spectroscopy were used to investigate the initial reduction of polyoxometalates with hydrazine and the synthesis of polyoxometalates-stabilised Au° nanoparticles (POM@AuNP) from reduced polyoxometalates/oxidized polyoxometalates, and metal precursors. In a solid-state system, polyoxometalates-stabilised metal nanoparticles (POM@MNP) (M=Au, Ag) are also prepared by using polyoxometalates as stabilisers in the presence of sodium borohydride using a ball mill. Chapter 5 describes the synthesis and characterization of a range of polyionic liquid immobilized Lindqvist-type polyoxometalates ([MW5]@PIIL), where [MW5]= (TBA)3[(MeO)4TiW5O18], (TBA)6[{MnW5O18H}2], (TBA)6[{FeW5O18H}2], and (TBA)6[{CoW5O18H}2]. [(MeO)TiW5O18]3-@PIIL (TiW5@PIIL), [{MnW5O18}2]3-@PIIL (MnW5@PIIL), [{FeW5O18}2]3-@PIIL (FeW5@PIIL), [{CoW5O18}2]3-@PIIL (CoW5@PIIL) were prepared in methanol and acetonitrile solvent at room temperature. Various techniques, including solid-state NMR spectroscopy, thermogravimetric analysis (TGA), energy dispersive X-ray (EDX), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) have used to characterize all the prepared compounds.15 0Item Restricted Polymer based inhibition of Quroum sensing in Gram negative bacteria(2023-07-02) Alshalan, Rawan; Shepherd, JoeyBackground: Bacterial quorum sensing (QS) is involved in several pathogenic bacterial processes, such as production of tissue-destroying enzymes, pyocyanin, and rhamnolipids, and biofilm formation. QS -mediated infectious diseases caused by bacteria make QS an important target for the development of materials with a novel antibacterial mode of action. Aim: To evaluate the anti- QS ability of the polymer HB-PINPAM-HL, a hyperbranched poly(NIPAM) polymer with chain ends uniquely functionalised with homoserine lactone (HL), on two Gram-negative bacteria Chromobacterium violaceum CV026 and Pseudomonas aeruginosa PAO1. Method: The polymer HB-PNIPAM-HL was first assessed for inhibition of QS in the model organism Chromobacterium violaceum CV026, and then in the pathogen Pseudomonas aeruginosa PAO1 indirectly by measuring different virulence factors (VFs). Then, the differential gene expression of bacterial genes involved in QS and VFs pathways regulated by QS systems was directly assessed following treatment with HB-PNIPAM-HL and HBPNIPAM-succ, an intermediate polymer formed during the process of HB-PNIPAM-HL production . Further analyses of the effects of the polymers on human cells were performed, which included a cytotoxicity assay and a wound healing assay (migration assay). Subsequently, the anti-QS actions of the two polymers were tested in early (2h) and late (24h) P.aeruginosa infections in a tissue-based wound infection model. Results: HB-PNIPAM-HL at 128 μg/ml can significantly reduce production of the violacein pigment in C.violaceum CV026 and down-regulate the gene cviR, encoding the QS receptor, in addition to three genes directly encoding the violacein genes. HB-PNIPAM-HL incubated with P.aeruginosa at 256 μg/ml can significantly reduce the production of several VFs such as protease, elastase, pyocyanin, rhamnolipids and biofilm, anti-QS. There was no cytotoxic effect on either of the cell lines tested at up to 512 μg/ml. In the wound healing assay, there was no significant delay in cell migration and wound healing at up to 512 μg/ml of HBPNIPAM-HL, and 256 μg/ml of HB-PNIPAM -succ. In a three-dimensional tissue engineered human skin wound infection model infected with P.aeruginosa, application of HB-PNIPAM-HL at up to 512 μg/ml resulted in less tissue destruction when applied 2 hours after infection, but not when applied late, 24 hours after infection. Conclusion: HB- PNIPAM-HL and HB-PNIPAM -succ show promising anti- QS properties by reducing the virulence and pathogenicity of P.aeruginosa. These polymers could be an alternative to conventional antibiotics and a promising non-antibiotic therapy for wound infections.20 0