Distributions of transverse relaxation times for soft-solids measured in strongly inhomogeneous magnetic fields

Abstract

The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG 1H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/ T 2,short and 1/ T 2,long were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium to large values of cross-link density. As an alternative to multi-exponential fits the possibility to analyze the dynamics of soft polymer network in terms of multi-exponential decays via the inverse Laplace transformation was studied. The transient regime and the effect of the T 1/ T 2 ratio in inhomogeneous static and radiofrequency magnetic fields on the CPMG decays were studied numerically using a dedicated C++ program to simulate the temporal and spatial dependence of the CPMG response. A correction factor T 2/ T 2,eff is derived as a function of the T 1/ T 2 ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T 1– T 2 correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T 1– T 2 experimental correlations maps were corrected for the T 1/ T 2 effect using the derived T 2/ T 2,eff correction factor.