Physics Department, Sapienza University of Rome, P.le A.Moro, 5 00185 Rome, Italy.
J Chem Phys. 2011 Jul 21;135(3):034504. doi: 10.1063/1.3610367.
In this paper, we describe nuclear magnetic resonance measurements of water diffusion in highly confined and heterogeneous colloidal systems using an anomalous diffusion model. For the first time, temporal and spatial fractional exponents, α and μ, introduced within the framework of continuous time random walk, are simultaneously measured by pulsed gradient spin-echo NMR technique in samples of micro-beads dispersed in aqueous solution. In order to mimic media with low and high level of disorder, mono-dispersed and poly-dispersed samples are used. We find that the exponent α depends on the disorder degree of the system. Conversely, the exponent μ depends on both bead sizes and magnetic susceptibility differences within samples. The new procedure proposed here may be a useful tool to probe porous materials and microstructural features of biological tissue.
本文采用异常扩散模型，通过核磁共振测量方法，对高度受限且不均匀胶体系统中的水扩散进行了研究。本文首次在连续时间无规行走的框架内，通过脉冲梯度自旋回波 NMR 技术，同时测量了微珠在水相溶液中分散样品的时间和空间分数阶指数α和μ。为了模拟低无序度和高无序度的介质，本文使用了单分散和多分散的样品。结果发现，指数α取决于系统的无序程度。相反，指数μ既取决于珠粒大小，又取决于样品内的磁导率差异。本文提出的新方法可能是探测多孔材料和生物组织微观结构特征的有用工具。
