Model for the interpretation of nuclear magnetic resonance relaxometry of hydrated porous silicate materials.
Model for the interpretation of nuclear magnetic resonance relaxometry of hydrated porous silicate materials.
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DOI：
10.1103/physreve.91.032311
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
D. Faux;S. Cachia;P. J. McDonald;J. Bhatt;N. C. Howlett;Sergey V. Churakov
中科院分区：
文献类型：
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作者：
D. Faux;S. Cachia;P. J. McDonald;J. Bhatt;N. C. Howlett;Sergey V. Churakov
核磁共振弛豫实验是探测多孔介质中质子自旋动力学的有效技术，但解释需要应用适当的自旋扩散模型。对含有准二维充水孔隙的多孔硅酸盐体系进行了分子动力学（MD）模拟。MD模拟表明，水在孔表面上的停留时间在0.03-12 ns的范围内，通常比使用科尔布及其同事[Phys.Rev.E56，1934（1997）]建立的表面层（SL）扩散模型拟合实验NMR测量值所确定的值小2-5个数量级。相反，MD确定了四个不同的水层中的雪硅钙石为基础的孔含有表面Ca 2+离子。三个高度结构化的水层存在于1 nm的表面和孔的中心区域包含一个均匀的区域的bulklike水。这些区域分别被称为层1和2（L1，L2）、过渡层（TL）和体（B）。在分子动力学模拟的指导下，提出了一个两层（2L）自旋扩散NMR弛豫模型，该模型包括两个二维层，分别与L2和TL+B层相关的慢速和快速移动的水。与SL模型相比，2L模型提供了对从胶凝材料获得的NMR弛豫时间的改进的拟合，产生与MD良好一致的在18-75 ns和28-40 ps范围内的扩散相关时间，并且解决了表面驻留时间差异。2L模型，再加上NMR弛豫实验，提供了一个简单而强大的方法来表征质子轴承多孔硅酸盐为基础的系统，如多孔玻璃，胶结材料，含油岩石的动力学性质。
Nuclear magnetic resonance (NMR) relaxation experimentation is an effective technique for probing the dynamics of proton spins in porous media, but interpretation requires the application of appropriate spin-diffusion models. Molecular dynamics (MD) simulations of porous silicate-based systems containing a quasi-two-dimensional water-filled pore are presented. The MD simulations suggest that the residency time of the water on the pore surface is in the range 0.03-12 ns, typically 2-5 orders of magnitude less than values determined from fits to experimental NMR measurements using the established surface-layer (SL) diffusion models of Korb and co-workers [Phys. Rev. E 56, 1934 (1997)]. Instead, MD identifies four distinct water layers in a tobermorite-based pore containing surface Ca2+ ions. Three highly structured water layers exist within 1 nm of the surface and the central region of the pore contains a homogeneous region of bulklike water. These regions are referred to as layer 1 and 2 (L1, L2), transition layer (TL), and bulk (B), respectively. Guided by the MD simulations, a two-layer (2L) spin-diffusion NMR relaxation model is proposed comprising two two-dimensional layers of slow- and fast-moving water associated with L2 and layers TL+B, respectively. The 2L model provides an improved fit to NMR relaxation times obtained from cementitious material compared to the SL model, yields diffusion correlation times in the range 18-75 ns and 28-40 ps in good agreement with MD, and resolves the surface residency time discrepancy. The 2L model, coupled with NMR relaxation experimentation, provides a simple yet powerful method of characterizing the dynamical properties of proton-bearing porous silicate-based systems such as porous glasses, cementitious materials, and oil-bearing rocks.