Effects of Micropores on the Vapor Sorption Isotherm and Structural Parameters Characterization of Kaolinite

The vapor sorption isotherm (VSI) of soil serves as a basic tool in geotechnical engineering, widely employed for characterizing the structural parameters of soil. Micropores are commonly found in soil, significantly altering the VSI and impacting the characterization of structural parameters. Nonetheless, these micropores are often overlooked in relevant analyses. Moreover, the characterization process relies on the utilization of theoretical models to fit the VSI. However, the commonly used models are not designed for VSI, raising concerns about their reliability. To investigate the influence of micropores on VSI and assess the reliability of various characterization models, this study used molecular simulation techniques to generate VSIs for kaolinite samples with different pore sizes. The simulation results reveal the effects of pore size on VSI shape, shed light on the influence of soil surfaces on pore water density and orientation, and highlight the important role of hydrogen bonds in water retention within the kaolinite pores. Furthermore, the reliability of three structural parameter characterization models, namely BET, DR, and a_s plot, was evaluated with the aid of the explicit geometric dimensions in molecular models, and the mechanisms responsible for their reliability were elucidated. This study deepens the understanding of VSI and provides crucial references for the characterization of soil structural parameters.