Hemmen H, Alme L R, Fossum J O, Meheust Y
Department of Physics, Norwegian University of Science and Technology, Hoegskoleringen 5, N-7491 Trondheim, Norway.
Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Sep;82(3 Pt 2):036315. doi: 10.1103/PhysRevE.82.036315. Epub 2010 Sep 20.
The swelling of layered smectite clay particles consists of a change in the interlayer repetition distance ( d -spacing) as a function of temperature and humidity. For the synthetic clay sodium fluorohectorite, hydrodynamically stable hydration states with zero, one and two intercalated monolayers of water have previously been reported, with discrete jumps in d -spacing at the transitions between the hydration states. Keeping the temperature fixed and varying the ambient relative humidity, we find small reproducible d -spacing changes also within the hydration states. These changes are monotonous as a function of relative humidity, and one order of magnitude smaller than the shift in d -spacing that is typical of the transition between two hydration states. The reproducibility and reliability of this relative humidity controlled d -shift enables us to use the interlayer repetition distance d as a measure of the local humidity surrounding the clay particles. We provide an example of application of this observation: imposing a humidity gradient over a quasi-one-dimensional temperature-controlled sample, and using x-ray diffraction to record the d -spacing, we are able to extract profiles of the relative humidity along the sample length. Their time evolution describes the transport of water through the mesoporous space inside the clay. An analysis of the measured humidity profiles based on the Boltzmann transformation, under certain simplifying assumptions, yields a diffusive behavior that is either normal or possibly weakly anomalous.
层状蒙脱石粘土颗粒的膨胀表现为层间重复距离（d间距）随温度和湿度的变化。对于合成粘土氟代锂蒙脱石，此前已报道了具有零、一和两个插层水单层的流体动力学稳定水合状态，在水合状态转变时d间距会有离散跳跃。保持温度不变，改变环境相对湿度，我们发现在水合状态内d间距也有小的可重复变化。这些变化随相对湿度单调变化，比两个水合状态之间典型转变时d间距的变化小一个数量级。这种相对湿度控制的d位移的可重复性和可靠性使我们能够将层间重复距离d用作粘土颗粒周围局部湿度的度量。我们给出了这一观察结果的应用示例：在准一维温度控制的样品上施加湿度梯度，并使用x射线衍射记录d间距，我们能够提取沿样品长度的相对湿度分布。它们随时间的演变描述了水在粘土内部介孔空间中的传输。在某些简化假设下，基于玻尔兹曼变换对测量的湿度分布进行分析，得出的扩散行为要么是正常的，要么可能是弱反常的。
