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Structural and Magnetic Properties of Biocompatible Iron Oxide Nanoparticles for Medical Applications
No full textThis thesis presents a comprehensive investigation of the structural and magnetic properties of biocompatible iron oxide nanoparticles coated with three different ligand materials: sodium citrate, (3-aminopropyl)triethoxysilane (APTES), and dextran. The influence of the coating agents on the agglomeration of iron oxide nanoparticles and their oxidation stability over time was studied. Various experimental techniques were used to characterize the structural and magnetic properties of the coated nanoparticles, including cryogenic transmission electron microscopy (cryo-TEM), magnetometry, and small-angle X-ray and neutron scattering. The results show that the coatings successfully stabilize the particles leading to various aggregate structures and sizes. These samples exhibit large saturation magnetization levels close to those of bulk iron oxide and a small coercivity as evidenced by the magnetization hysteresis loop at room temperature. We find that the zero-fieldcooled (ZFC) and field-cooled (FC) magnetization behaviour is influenced by magnetic interactions among the nanoparticles inside clusters. The interaction leads to a shift of the blocking temperature to higher values and a flattening of the FC curves at lower temperatures. Notably, the blocking temperature of the citrate-coated samples were lower than would have been expected for the large clustered structure. Furthermore, for this sample magnetic small-angle neutron scattering (SANS) reveals a multidomain structure, with the magnetic size corresponding to half of the cluster size as observed by SAXS. In the aging study, M¨ossbauer spectroscopy was used to follow the changes in Fe2+ and Fe3+ composition over time, while magnetometry allowed the determination of the net magnetization. In all systems, rapid oxidation was observed after less than 0.1 days (the time between the end of synthesis and the sealing of the samples under N2 atmosphere). This led to a complete oxidation of the magnetite nanoparticles to maghemite with the dextran coating, while the nanoparticles with citrate and APTES coating showed slower oxidation with 10% - 20% of the magnetite fraction after one month. The variation inoxidation behaviour is linked to the variations in particle size, which in turn are influenced by the coating agent and the synthesis method. Micromagnetic simulations were performed with the Object Oriented Micromagnetic Framework (OOMMF) software for ensembles of randomly arranged and randomly connected nanoparticles. The ”Theta Evolver” within OOMMF was used to include thermal fluctuations of the magnetic superspin moments of the nanoparticles to model the ZFC and FC curves, in addition to the magnetization hysteresis loops. The simulation results help us to understand the effect of exchange and dipolar inter-particle interactions on the energy barriers for magnetization reversal and, thus, on the magnetization hysteresis curves. This knowledge of the altered magnetic behaviour is required in tuning the synthesis route to obtain the desired magnetic properties for future medical applications. Part of the results presented in this thesis was published in Ref. [1], and a secondmanuscript on micromagnetic simulations is in preparation
Optical Determination of Hydrofluoric Acid Content in Lithium-Based Electrolytes
No full textLithium-ion batteries powering electric vehicles can contain up to ∼100 liters of electrolyte solution. This solution typically consists of LiPF6 salt dissolved in a mixture of organic carbonates such as ethylene carbonate and diethyl carbonate. LiPF6 decomposes upon exposure to water vapor or other protic impurities, leading to the formation of up to 3 equivalents of hydrofluoric acid (HF) per molecule of decomposed salt. HF is a deadly and volatile substance that is corrosive to cell and battery components. Here, we describe an all-optical method that can report on the concentration of HF in LiPF6-based electrolytes. The method is based on a specially designed fluorescent dye incorporated in the working electrolyte. The dye response to HF is quantified so that photographic imaging or even visual inspection can be used to indicate the HF concentration in the electrolyte. The method is, moreover, compatible, in principle, with in situ reporting of HF levels during cell assembly and operation
The AEgIS Experiment: Progress and Future Outlook
No full textThe AEgIS experiment at CERN is pioneering measurements of gravity, spectroscopy, and interferometry using pulsed antimatter atomic sources. This work provides an overview of the AEgIS experimental setup and highlights recent advancements in antihydrogen production, positronium laser cooling, and the creation of antiprotonic atoms. Key technological developments, including the overhaul of the control system and its impact on precision experiments, are reviewed. Future perspectives for AEgIS before CERN Long Shutdown 3 and beyond are summarized
