A novel approach for advanced thermoporometry characterization of mesoporous solids: Transition kernels and the serially connected pore model

Thermoporometry, namely revealing pore sizes based on the shifts of the freezing and melting transitions of liquid in the pores, has proven a powerful approach for mesostructure characterization of porous solids. Complementary to gas adsorption, it has several advantages, such as applicability to wet samples. At the same time, while gas sorption characterization has largely profited from the recent advances in the understanding of the gas-liquid phase equilibria in confined spaces, the solid-liquid transitions have remained poorly covered. In this work, in an analogy to the advanced gas sorption analysis, we implement a novel approach in thermoporometry by introducing the transition kernels, i.e. the families of solid-liquid transition curves describing different transition scenarios in single pores. In this way, a variation of the non-frozen layer thickness with temperature and the effects of thermodynamic fluctuations on phase transitions become automatically encoded in the transition kernels. As a next step, we incorporate these kernels into a recently developed theoretical framework, the serially-connected pore model, allowing for the analysis of pore networks beyond collections of independent pores conventionally assumed in the literature. This combination yields a substantial improvement of the accuracy of the thermoporometry method which is further demonstrated by applying NMR cryoporometry to MCM-41 and SBA-15 materials.