Publikationsserver der RWTH Aachen University
Investigation of material properties by NMR in low and high magnetic fields
Abstract
dc:descriptionNMR is a powerful method of investigation with a wide range of applications. Magnetic resonance is used in medicine, the oil industry, food industry, for chemical analysis, quality control in industry and construction, analysis of cultural heritage, and materials science, in particular polymer analysis. The unique feature of NMR is the non-destructive approach, making this method a suitable technique for measuring works of art or for complex in vivo experiments. The investigation of material properties is one of the most important goals of NMR. The mobile sensors developed lately make measurements possible at remote locations for some historical buildings or measuring rocks at the drilling platform minutes after the extraction. In this work the experiments have been performed at both low and high field. The experiments cover various domains from simple relaxation experiments in low field to diffusion and spin-diffusion in high field. The measurements of porosity and pore size distribution are made with the help of a new mobile magnet, the Halbach magnet. The Halbach scanner has a higher sensitivity than the NMR MOUSE®. The Hahn and stimulated echoes have been implemented for diffusion measurements in a new single sided NMR sensor. The profile NMR MOUSE strong and uniform gradient make this magnet perfect for diffusion experiments, even for high viscosity liquids or restricted diffusion in porous media, like tendon or rubber. The applications of low-field investigations are: - quality control of chemical products.- water content determination inside of the walls of buildings.- determination of multilayer polymer coatings on a concrete.In high-field NMR several alkane molecules swollen at equilibrium in cross-linked natural rubber samples have been investigated and analyzed based on the assumptions of the Vrentras theory. A small diffusion anisotropy of the order of 10% has been discovered because of a deformation of free volume under compression. The anisotropy increases with the cross-link density and the compression ratio. The results presented in this study show that the solvent size influences the anisotropy of the diffusion process through the size parameter. Hence, information on the effect of solvent size, shape, and flexibility on the diffusion process can be refined by measuring the size parameter anisotropy for a variety of solvents diffusing in different polymers.The spin-diffusion measurements have been performed on Stanyl samples with different aged samples, at controlled temperature conditions. The amount of rigid phase increases at the end of the aging process and the segmental mobility is reduced due to the ordering of polymer chains from the interface and due to polymer chain packing. A process of disordering in the crystalline structure followed by reorganization takes place in the range of 60-200 hours of aging time. An opposite process is present for the interphase. The most probable morphology is one-dimensional for the PA46 samples in the full range of aging times. The correlation of macroscopic, mesoscopic, and microscopic material properties can be used to reach a deeper understanding of heterogeneous polymers. To summarize, in this work we have approached various types of NMR investigations. The common goal of these experiments is to reach a deeper understanding of the material microstructure, using various techniques and combining the information obtained. Methods like restricted diffusion can give information about structures with several orders of magnitude smaller then other conventional techniques and spin-diffusion is the only investigation capably to give information about the interface and the amorphous regions. In conclusion, NMR is a important investigation technique, with many applications discovered in its 60 years of existence, and has many more fields of research waiting to be explored.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2006
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Rata, Doru Gabriel
- Contributors dc:contributor
-
- Blümich, Bernhard
Subjects
dc:subject × 8Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng
Identifiers
dc:identifier.*- OAI identifier oai:identifier
- oai:publications.rwth-aachen.de:61299