Nuclear Magnetic Resonance, Imaging of Polymers

Abstract

Nuclear magnetic resonance (NMR) imaging is a non‐invasive technique which is based on the phenomenon of NMR. The resonance frequencies of the nuclear spins can be made spatially dependent by introducing a magnetic field gradient into the NMR experiment. The acquired NMR signal is thus spatially encoded and a spin‐density image of the sample can be reconstructed. While originally developed for medical applications, NMR imaging is now increasingly applied for materials investigations. The main advantages of the technique are its nondestructivity, which allows processes to be investigated in situ, and the possibility of introducing NMR spectroscopic information and relaxation contrast into the NMR images. Limitations, on the other hand, are the relatively low sensitivity and the broad NMR lines of polymers, both of which limit the spatial resolution. Whereas the latter can be dealt with by suitable methods, the sensitivity ultimately restricts the achievable spatial resolution of conventional NMR imaging techniques to about 10µm 3 . NMR imaging therefore must not be considered as a competitor of other microscopic techniques such as electron microscopy but as a characterization technique that provides supplementary information. Examples illustrating all these aspects are given in this article.