Journal
MATERIALS
Volume 15, Issue 7, Pages -Publisher
MDPI
DOI: 10.3390/ma15072350
Keywords
porous solids; phase equilibria; nitrogen sorption; NMR cryoporometry; thermoporometry; mercury porosimetry
Categories
Funding
- German Science Foundation (DFG) [411771259]
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This study compares phase transitions in mesoporous silica solids with different pore sizes, and finds that thermodynamic fluctuations become more important and have different effects on different equilibria as the pore size decreases.
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.
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