Enninful Henry R N B, Enke Dirk, Valiullin Rustem
Felix Bloch Institute for Solid State Physics, Leipzig University, 04103 Leipzig, Germany.
Institute for Technical Chemistry, Leipzig University, 04103 Leipzig, Germany.
Materials (Basel). 2022 Mar 22;15(7):2350. doi: 10.3390/ma15072350.
Alterations of fluid phase transitions in porous materials are conventionally employed for the characterization of mesoporous solids. In the first approximation, this may be based on the application of the Kelvin equation for gas-liquid and the Gibbs-Thomson equation for solid-liquid phase equilibria for obtaining pore size distributions. Herein, we provide a comparative analysis of different phase coexistences measured in mesoporous silica solids with different pore sizes and morphology. Instead of comparing the resulting pore size distributions, we rather compare the transitions directly by using a common coordinate for varying the experiment's thermodynamic parameters based on the two equations mentioned. Both phase transitions in these coordinates produce comparable results for mesoporous solids of relatively large pore sizes. In contrast, marked differences are found for materials with smaller pore sizes. This illuminates the fact that, with reducing confinement sizes, thermodynamic fluctuations become increasingly important and different for different equilibria considered. In addition, we show that in the coordinate used for analysis, mercury intrusion matches perfectly with desorption and freezing transitions.
多孔材料中流体相转变的变化通常用于表征介孔固体。在一阶近似中，这可能基于应用开尔文方程描述气-液相平衡以及吉布斯-汤姆逊方程描述固-液相平衡来获得孔径分布。在此，我们对在具有不同孔径和形态的介孔二氧化硅固体中测量的不同相共存情况进行了比较分析。我们不是比较所得的孔径分布，而是基于上述两个方程，通过使用一个用于改变实验热力学参数的公共坐标来直接比较转变。在这些坐标中，对于孔径相对较大的介孔固体，两种相转变产生了可比的结果。相比之下，对于孔径较小的材料发现了明显差异。这说明了随着受限尺寸的减小，热力学涨落变得越来越重要，并且对于所考虑的不同平衡是不同 的。此外，我们表明，在用于分析的坐标中，压汞与脱附和冻结转变完美匹配。
