CEA, DEN, DTN Cadarache, F-13108 Saint Paul Les Durance, France.
Langmuir. 2010 Apr 6;26(7):5028-37. doi: 10.1021/la1002868.
The osmotic character of long-range interlamellar swelling in smectite clays is widely accepted and has been evidenced in the interlayer space by X-ray diffraction. Such a behavior in mesopores was not experimentally confirmed until the determination of the mesopore size distribution in Na-montmorillonite prepared from MX80 bentonite using thermoporometry experiments. This is confirmed here for other montmorillonite samples where the interlayer cations are alkaline and Ca(2+) cations. The nature of the interlayer cation is found as strongly influencing the behavior of the size and the swelling of mesopores. These results are supported by the BJH (Barrett, Joyner and Halenda) pore radius values issued from the nitrogen adsorption-desorption isotherms at the dry state. Thermoporometry results as a function of relative humidity ranging from 11% to 97% have shown an evolution of the mesopore sizes for a purified Na-montmorillonite. New thermoporometry data are presented in this article and confirm that the interparticle spaces in K-, Cs-, or Ca-montmorillonites are not strongly modified for all the range of relative humidity: the swelling is not observed or is strongly limited. It appears in contrast that only Li- and Na-montmorillonites undergo a mesopore swelling, distinct from the interlayer swelling. More generally, our results confirm the possibility to use thermoporometry or differential scanning calorimetry to study the structure and the evolution of swelling materials in wetting conditions such as natural clays or biological cells. In this paper, we describe the different key steps of the hydration of swelling clays such as montmorillonites saturated with alkaline cations. Using thermoporometry results combined with X-ray diffraction data, we distinguish the evolution of the porosity at the two different scales and propose a sequence of hydration dependent on the interlayer cation. From this study, it is shown that the interlayer spaces are not completely filled when the mesopores start to fill up. This implies that the swelling observed in the mesopores for Li and Na samples is due to an osmotic swelling. For the other samples, it is difficult to conclude definitively. Furthermore, we determine the different proportion of water (interlayer water and mesopore water) present in our samples by the original combination of (1) X-ray diffraction data, (2) the pore size distribution obtained by thermoporometry, and (3) recent adsorption isotherm results. It is found that the interlayer space is never completely filled by water at the studied relative humidity values for all samples except for the Cs sample.
蒙皂石粘土的长程层间膨胀的渗透特性已被广泛接受，并通过 X 射线衍射在层间空间得到证实。直到通过热导法实验确定从 MX80 膨润土制备的 Na-蒙脱石的中孔尺寸分布，这种行为才在中孔中得到实验证实。在这里，对于其他层间阳离子为碱性和 Ca(2+)阳离子的蒙脱石样品也得到了证实。层间阳离子的性质被发现强烈影响中孔的尺寸和膨胀行为。这些结果得到了在干燥状态下从氮气吸附-解吸等温线得出的 BJH（Barrett、Joyner 和 Halenda）孔径值的支持。相对湿度范围为 11%至 97%的热导法结果表明，纯化的 Na-蒙脱石的中孔尺寸发生了变化。本文提出了新的热导法数据，证实了 K-、Cs-或 Ca-蒙脱石中的颗粒间空间在整个相对湿度范围内不会发生强烈变化：不会观察到或强烈限制膨胀。相反，只有 Li-和 Na-蒙脱石经历了中孔膨胀，与层间膨胀不同。更一般地说，我们的结果证实了使用热导法或差示扫描量热法研究润湿条件下（如天然粘土或生物细胞）结构和膨胀材料演变的可能性。在本文中，我们描述了饱和有碱性阳离子的蒙脱石等膨胀粘土的水化的不同关键步骤。结合热导法结果和 X 射线衍射数据，我们区分了两个不同尺度上的孔隙率演变，并提出了一个依赖于层间阳离子的水化序列。从这项研究中可以看出，当中孔开始填充时，层间空间并未完全填满。这意味着 Li 和 Na 样品中观察到的中孔膨胀是由于渗透压膨胀。对于其他样品，很难得出明确的结论。此外，我们通过（1）X 射线衍射数据、（2）通过热导法获得的孔径分布以及（3）最近的吸附等温线结果的原始组合，确定了我们样品中存在的不同比例的水（层间水和中孔水）。结果发现，除了 Cs 样品外，在所研究的相对湿度值下，所有样品的层间空间都从未完全被水填满。
