Explicit calculation of nuclear-magnetic-resonance relaxation rates in small pores to elucidate molecular-scale fluid dynamics
Explicit calculation of nuclear-magnetic-resonance relaxation rates in small pores to elucidate molecular-scale fluid dynamics
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DOI：
10.1103/physreve.95.033117
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发表时间：
2017-03-28
影响因子：
2.4
通讯作者：
McDonald, P. J.
中科院分区：
文献类型：
--
作者：
Faux, D. A.;McDonald, P. J.
核磁共振（NMR）自旋-晶格（T-1(-1)）和自旋-自旋（T-2(-1)）弛豫速率测量可以作为多孔介质中H-1自旋纳米尺度动力学的有效无损探针。特别是，快速场循环的T-1（-1）色散测量包含了在跨越许多数量级的时间尺度上扩散自旋的动力学信息。先前发表的实验T-1（-1）分散体来自石膏膏、合成皂石、砂浆和含油页岩，使用模型和相关理论重新分析，该模型和相关理论描述了准二维孔隙中自旋系综之间相互作用导致的弛豫速率贡献。该模型的应用为所有系统产生了物理上有意义的扩散相关时间。特别是，每个体系的表面扩散相关时间和表面脱附时间的值相似，表明表面迁移率和脱附是相互联系的过程。发现每个系统的体积流体扩散相关时间是室温下纯液体值的2到5倍。对含油页岩的重新分析得到了油和水组分的扩散时间常数。页岩具有油润湿性，水的T-1（-1）分散性与水体中Mn2+顺磁杂质有关。这些结果提升了核磁共振T-1（-1）分散测量技术作为多孔介质中分子尺度动力学的主要探针，产生了扩散参数和丰富的孔隙形态信息。
Nuclear-magnetic-resonance (NMR) spin-lattice (T-1(-1)) and spin-spin (T-2(-1)) relaxation rate measurements can act as effective nondestructive probes of the nanoscale dynamics of H-1 spins in porous media. In particular, fast-field-cycling T-1(-1) dispersion measurements contain information on the dynamics of diffusing spins over time scales spanning many orders of magnitude. Previously published experimental T-1(-1) dispersions from a plaster paste, synthetic saponite, mortar, and oil-bearing shale are reanalyzed using a model and associated theory which describe the relaxation rate contributions due to the interaction between spin ensembles in quasi-two-dimensional pores. Application of the model yields physically meaningful diffusion correlation times for all systems. In particular, the surface diffusion correlation time and the surface desorption time take similar values for each system, suggesting that surface mobility and desorption are linked processes. The bulk fluid diffusion correlation time is found to be two to five times the value for the pure liquid at room temperature for each system. Reanalysis of the oil-bearing shale yields diffusion time constants for both the oil and water constituents. The shale is found to be oil wetting and the water T-1(-1) dispersion is found to be associated with aqueous Mn2+ paramagnetic impurities in the bulk water. These results escalate the NMR T-1(-1) dispersion measurement technique as the primary probe of molecular-scale dynamics in porous media yielding diffusion parameters and a wealth of information on pore morphology.