Note: Status July 2022 - Topics may change at short notice. All topics are in principle suitable as a master's thesis, as well as a bachelor's thesis, if indicated. For further inquiries please contact by email or phone:
Siegfried Stapf, Tel. 3671 - Carlos Mattea, Tel. 3787
- 1. NMR study on the solid fraction in solutions with microplastics (Bachelor) How can the solid content of polymers be quantified in a simple and fast way using NMR pulse sequences? Which magnetic field strength is optimal?Current and planned EU guidelines for minimizing microplastics in the environment include definitions of size and strength; however, the latter in particular is not practical for aqueous solutions and multicomponent systems. New and efficient methods to determine the solid fraction are sought, and NMR relaxation is an obvious choice: viscous and solid materials are characterized by shorter T2 times as well as specific magnetic field dependencies ofT1 times. Using model polymers (e.g. PVP), measurement methods and correlations will be established; the project is carried out in close cooperation with the global research of BASF SE/Ludwigshafen. Focus: experiment, data analysis
- 2. relaxation and diffusion of liquids in mesoporous silica (Bachelor) How do molecular dynamics change within regular pores of a few nm diameter? Does diffusion depend on molecule size or polarity?NMR relaxation of adsorbed liquids in mesoporous glass (i.e., pore sizes below 50 nm) depends strongly on the polarity of the molecules and the nature of the interaction with the surface. Previous studies dealt with materials in the disordered pore structure of glasses. This work deals with man-made cylindrical silica structures (SBA-15) with hexagonal cross section from 4 to 12 nm in diameter and aims to measureT1 and T2 relaxation times of polar and nonpolar adsorbates and determine their diffusion coefficients using a desktop NMR spectrometer. They will be complemented, where appropriate, by 2H experiments in a field of 7 T. Focus: preparation, experiment
- 3. aging of engine and lubricating oil (Bachelor/Master) How can the aging and degradation of engine oil be characterized using ESR and NMR?When engine oil is used in automobiles and other vehicles, as well as lubricating oil in industrial equipment, thermal stress, as well as other external influences such as combustion, contamination, light, etc., cause decomposition processes that require the renewal of the oil after a certain period of time. The lifetime of the oil is estimated empirically, but depends on the exact working conditions; detailed analysis on viscosity, chemical composition, mechanical properties, transparency, etc. has proven to be laborious and not universally applicable. Since the degradation of the oil is usually accompanied by the formation of stable radicals, ESR spectroscopy is a simple and fast (less than 1 min) method for quality control. Different precursor oils (without additives) and commercial products (with antioxidants and further additives) will be investigated for their stability, passing through different cycles of heating, UV treatment and oxidation; the correlation of the radical concentration with these parameters will be checked. If necessary, complementary NMR relaxation measurements will be performed, since the presence of radicals can also manifest itself in the relaxation times.The project is carried out in cooperation with the Universidad Nacional de Cordoba, Argentina.Focus: sample handling, experiment, documentation
- 4. NMR multipulse method for polymers and ordered systems (Bachelor/Master) How can the mean displacement square of molecules be determined using novel echo techniques? What are the possible applications for biological samples and porous media?A robust multiecho method has been developed for dynamics in polymer melts, which determines the mean displacement square for anomalous diffusion (subdiffusive processes) in a time domain that is not accessible by other methods. The method will now be applied to new polymers, biomacromolecules, and liquids in porous media. The device allows for temperature control down to about 470 K.Emphasis: Experiment, data analysis, theory
- 5. deuterated polymer blends in confinement (Bachelor/Master) How does confinement in narrow pores affect the dynamics of polymer melts?In the department we are working on a long-standing project to analyze polymer melts using different isotope diluted mixtures of polyethylene oxide (both 1Hand 2H resonance). One aspect of the DFG project investigates the question of what differences in dynamics arise during confinement in rigid porous media (e.g., Vycor glass, 4 nm, as an established standard). In the literature, only measurements of undereuterated PEO have been successful so far.Emphasis: Sample preparation, experiment
- 6. multifunctional hydrogels in natural soils (Bachelor/Master) How does the storage capacity for water in soils change with the addition of hydrogels?Globally, water availability for agriculture is important in addition to precipitation distribution - in 2019/20 soils in Germany are massively undersaturated, water cannot be adequately retained without active plant components. Hydrogels can store large amounts of water and also release it in interaction with plant roots, their use on a large scale is being prepared. NMR can be used to measure the amount as well as the binding state and the mobility of water, MRI can additionally be used to visualize the gel distribution (the latter only in the context of a master thesis). Cooperation with FZ Jülich.Main focus: Experiment, literature study, data analysis.
- 7. rheology on polymer melts in a magnetic field (Master) Can mechanical stress measurably influence molecular dynamics?Use of an existing apparatus for systematic analysis of the change in NMR relaxation properties of sheared polymer melts and possibly other complex fluids with spectral resolution. Measurements in either high field or variable field (field-cycling relaxometer). Emphasis: Sample preparation, measurement; documentation and optimization of measurement parameters; data analysis and literature.
- 8. construction of a unit with field modulation tracks (Master) How to size field modulation coils to perform Integrated Solid Effects?Dynamic Nuclear Polarization (DNP) is one of the techniques currently used for signal enhancement in NMR; it relies on microwave irradiation. However, for many substances with broad absorption lines, excitation by MIcrowaves is much too weak; here, the magnetic field must be modulated at high frequency to cover the entire width of the (electron) spectrum. For this purpose, additional coils have to be constructed that are close to the sample to minimize the necessary current and heating effects. The design is based on commercial solutions for field gradient coils.Emphasis: Design, construction - electronics skills.