• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Applied Magnetic Resonance >Time-dependent molecular diffusion in partially filled porous glasses with heterogeneous structure
【24h】

Time-dependent molecular diffusion in partially filled porous glasses with heterogeneous structure

机译：具有非均质结构的部分填充多孔玻璃中随时间变化的分子扩散

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Nuclear magnetic resonance (NMR) microscopy of silica glasses with micrometer pores (Vitrapor#5) partially filled with water or cyclohexane reveals a heterogeneous distribution of liquid on a length scale much longer than the pore dimension. This heterogeneity, which is not observed in MR imaging of saturated samples, is attributed to the spatial variation of the granular microstructure visible in scanning electron micrographs. As a consequence of an inhomogeneous filling degree, the effective transverse relaxation time varies, which in turn leads to NMR imaging contrasts. Since the spatial distribution of the transverse relaxation time prevents reliable measurements with a standard pulsed gradient stimulated echo technique, a combination of the fringe field stimulated echo method, on the one hand, and the magnetization grid rotating-frame imaging technique, on the other, was employed. Four decades of the diffusion time from 100 ms to 1 s can be covered on this basis. The data were compared with Monte Carlo simulations of a model structure showing a qualitatively equivalent behavior in the common time window. The self-diffusion in partially filled porous systems is known to be strongly affected by a vapor phase. Here we have shown that the vapor phase contribution to the effective diffusivity is particularly efficient on a diffusion time scale corresponding to mean-squares displacements of the order of the pore dimension.
机译：具有部分充满水或环己烷的微米孔（Vitrapor＃5）的石英玻璃的核磁共振（NMR）显微镜显示，液体的不均匀分布的长度比孔的尺寸长得多。这种异质性在饱和样品的MR成像中未观察到，这归因于在扫描电子显微照片中可见的颗粒微观结构的空间变化。由于填充程度不均匀，有效的横向弛豫时间会发生变化，进而导致NMR成像对比。由于横向弛豫时间的空间分布会妨碍使用标准脉冲梯度激励回波技术进行可靠的测量，因此一方面将边缘场激励回波方法与磁化栅格旋转框架成像技术相结合，被雇佣。在此基础上可以涵盖从100 ms到1 s的四十年的扩散时间。将数据与模型结构的蒙特卡洛模拟进行了比较，该模型显示了在公共时间窗口内的定性等效行为。已知部分填充的多孔系统中的自扩散会受到气相的强烈影响。在这里，我们已经表明，气相对有效扩散率的贡献在对应于孔径大小均方位移的扩散时间尺度上特别有效。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号