On the Comparative Analysis of Different Phase Coexistences in Mesoporous Materials

Area of Science:

• Materials Science
• Physical Chemistry
• Nanotechnology

Background:

• Characterizing mesoporous solids conventionally relies on fluid phase transitions.
• The Kelvin and Gibbs-Thomson equations approximate pore size distributions from gas-liquid and solid-liquid equilibria, respectively.

Purpose of the Study:

• To comparatively analyze phase transitions in mesoporous silica with varying pore sizes and morphologies.
• To evaluate the direct comparison of phase transitions using a unified thermodynamic coordinate, rather than relying solely on pore size distributions.

Main Methods:

• Experimental measurement of phase transitions (adsorption/desorption, freezing/melting) in mesoporous silica.
• Analysis of phase transition data using a common thermodynamic coordinate derived from the Kelvin and Gibbs-Thomson equations.
• Comparison of mercury intrusion with desorption and freezing transitions.

Main Results:

• Phase transitions yield comparable results for larger mesopores when analyzed in the unified coordinate.
• Significant differences emerge for smaller mesopores, highlighting the increasing importance of thermodynamic fluctuations.
• The chosen coordinate system demonstrates a perfect match between mercury intrusion, desorption, and freezing transitions.

Conclusions:

• Thermodynamic fluctuations play a critical role in phase transitions within confined nanoporous materials, especially as pore sizes decrease.
• The direct comparison of phase transitions in a unified thermodynamic coordinate offers a robust method for characterizing mesoporous materials.
• The validated coordinate system provides a consistent framework for understanding different phase equilibria in porous materials.