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Abstract
Hydrophilic and hydrophobic behaviors exhibited by microporous materials are critical to a wide range of mature and emerging technologies. However, robust explanations of the foundational underpinnings of this behavior remain elusive. An impediment to the advancement of fundamental understanding is the lack of analysis framework that is simultaneously capable of elucidating water interaction mechanisms and characterizing equilibrium isotherm types while providing a quantitative definition of hydrophobicity. To this end, the study herein develops such a framework that is demonstrably capable of dictating multiple isotherm types, ranging from hydrophilic to hydrophobic. A novel hydrophobicity map is utilized to indicate relationships between isotherm types and explicit forms of hydrophobicity. Applied to the assessment of 15 non-functionalized carbons, the nature of water in extreme confinement offered by angstrom sized pores is characterized by both bulk fluidic and molecular behavior. Accounting for fluid-solid and fluid-fluid-solid interaction, the angstrofluidic nature of water in microporous carbon appears to be remarkably similar to equivalent non-functionalized Metal-Organic Framework (MOF) materials and ensembles of graphene layers. Coupling molecular level with bulk fluid behavior, Ising Model- Modified Kelvin Analysis (IMMKA) provides a characterization methodology which identifies nanocapillarity and nanowetting components, partitions various forms of hydrophobicity and is presented in a simple, rigorous, analytic form. The analysis produces results that are consistent with independent data assessment, macroscopic observations of contact angle and the 10-4-3 potential model. Functionalized materials are also considered and novel relationships with surface functionality and fundamental angstrofluidic features of water are delivered herein. Critical to elucidation of hydrophobic phenomena and to novel technologies designed at the molecular level, this study provides validated means for further enhancing angstrofluidic descriptions of water in extreme confinement.
