(185c) Effect of Nano-Confinement on NMR Relaxation Using Atomistic Simulations
AIChE Annual Meeting
Monday, November 16, 2020 - 8:30am to 8:45am
Over the past several years, we have developed an approach to understand and elucidate the experimentally observed 1H NMR relaxation information using molecular simulations. A crucial outcome of these studies has been to expose the qualitative and quantitative limitations of traditional models of NMR relaxation that continue to be used in applications that span well-logging to interpreting MRI in biological systems.
Our initial studies had explored the role of intrinsic properties of the molecules, including its shape and internal motions. Building on that foundation, we have started probing the effect of the environment on the molecule's NMR relaxation behavior. In this talk, I will present our results on NMR relaxation behavior of alkanes confined in polymer matrix. We find that confinement increases 1H-1H dipole-dipole correlation times, which in-turn decreases the relaxation times. This is consistent with what is observed experimentally for polydisperse polymers and bitumen. The observations such as large T1/T2 ratios, and frequency dependence of T1, were previously attributed to paramagnetism; instead, our studies show this is due to enhanced dipole-dipole interactions in small organic nanopore confinement. We have further explored the confinement effect by studying heptane in a rigid mesoporous carbon matrix. Calculations show a striking similarity to the results for alkanes confined in the polymer matrix. Our studies suggest the possibility of building a general theory, to replace or augment the traditional theories, to describe NMR relaxation in complex systems.