Low frequency NMR relaxometry for the study of polymer dynamics

• Applicants: Professor Dr. Franz Fujara; Professor Dr. Ernst Rößler
• Subject Area: Experimental and Theoretical Physics of Polymers ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Polymer Materials
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 255348432

We plan to combine field-cycling (FC)- and field-gradient (FG)-NMR for studying the collective dynamics of linear polymer melts. The instrumental achievements of the first funding period will be used in a systematic way. For instance, the frequency dependent relaxation rate now covers a range from 40 MHz down to about 300Hz. Hints for deficiencies of the tube-reptation model shall be further examined for other polymer systems, and alternative models for the polymer dynamics will be considered. Further, discrepancies between our FC data, double quantum NMR data (K. Saalwächter, Halle) and generic simulations will be analyzed. The overall goal is to find out to which extent the tube-reptation model keeps its validity at a microscopic level. We plan to start measurements of the pure reorientation dynamics by looking for the first systematically at the 2H relaxation dispersion. These experiments will complement the determination of the intrachain 1H relaxation rate dispersion and the interchain rate dispersion, extracted from 1H/2H dilution experiments. The relative contribution of both provides valuable information on the microscopic dynamics and allows discriminating different polymer models. From the inter rate we will deduce the mean squared displacement (MSD) and combine these results with directly measured FG data. In this way we are able, for the first time, to cover the whole sub-diffusive regime in terms of the MSD. For the theory part we have gained Prof. N. Fatkullin (Kazan) as a coworker. Also, the instrumental development will be further pushed forward. We will try to reach down to 1H frequencies well below 100 Hz routinely, which is more than two orders of magnitude below those of commercial machines. With such a wide frequency span we can truly consider FC relaxometry as a powerful molecular rheology method for studying diverse soft matter systems.

• DFG Programme: Research Grants