Advances in the interpretation of frequency-dependent nuclear magnetic resonance measurements from porous material

Fast-field-cycling nuclear magnetic resonance (FFC-NMR) is a powerful technique for non-destructively probing the properties of fluids contained within the pores of porous materials. FFC-NMR measures the spin-lattice relaxation rate R1( f ) as a function of NMR frequency f over the kHz to MHz range. The shape and magnitude of the R1( f ) dispersion curve is exquisitely sensitive to the relative motion of pairs of spins over time scales of picoseconds to microseconds. To extract information on the nano-scale dynamics of spins, it is necessary to identify a model that describes the relative motion of pairs of spins, to translate the model dynamics to a prediction of R1( f ) and then to fit to the experimental dispersion. The principles underpinning one such model, the 3t model, are described here. We present a new fitting package using the 3t model, called 3TM, that allows users to achieve excellent fits to experimental relaxation rates over the full frequency range to yield five material properties and much additional derived information. 3TM is demonstrated on historic data for mortar and plaster paste samples.