Fast Field Cycling 19F NMR Relaxometry of Polytetrafluoroethylene.

Polytetrafluoroethylene (PTFE) has been widely used in various forms, and its properties are affected by its fabrication processes. We applied fast field cycling (FFC) NMR relaxometry to commercially available PTFE and related compounds to investigate their chain dynamics in the solid state. Four different types of commercially available PTFE samples (powder, tape, and films) were subjected to XRD, Raman, and DSC measurements, and the crystallinity of the two film samples was found to be lower than that of the powder and the tape. Spin-lattice relaxation rates decreased with increasing relaxation magnetic field strength, following a power law, as explained by the defect diffusion model. In some cases, deviations from the power law dependence at the upper limit of the relaxation magnetic field indicated the contribution of Rouse dynamics. Based on DFT calculations on model compounds with different defect types, kinks were considered to be diffusing defects.