EAGER/Collaborative Research: New Concept of Sorption Hysteresis and Disjoining Pressure in Concrete and Other Adsorbent Microporous Solids

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The objective of this EArly-Concept Grant for Exploratory Research (EAGER) project is to elucidate the cause of sorption hysteresis in hindered adsorbed layers in micropores, which has remained fundamentally unexplained for over 60 years. Two mechanisms are investigated. One consists of a series of snap-through instabilities during the filling or emptying of non-uniform pores, due to the non-uniqueness of the misfit disjoining pressure where the pore thickness passes through integer multiples of the monolayer thickness. The second consists of molecular coalescence, or segregation, within a partially filled layer, either by spinodal decomposition (linear instability of homogeneous filling) or by nucleation at defects or pore openings. At the macroscale, both mechanisms lead to heterogeneous filling or emptying across many parallel pores and large changes in the disjoining pressures calculated from thermodynamics. These changes are an essential part of any physical theory of drying creep and shrinkage. Another goal is to identify from sorption tests the pore size distribution and the internal surface area, and the third goal is the prediction of fluid transport through microporous solids. Sorption hysteresis in microporous solids controls microscale stresses which govern creep and inelastic deformations in and around the micropores and the energy dissipation during sorption. The energy dissipated by sorption cycles contributes to material damage. These phenomena are of fundamental interest for predicting the damage and creep in all kinds of concrete structures, release of methane from coal deposits, gas sequestration capacity of rock, gas release from shale, etc. A course incorporating the subject of the proposal will be developed. The work will contribute to the education of both undergraduate and graduate students. Undergraduates will be involved on a special-purpose work-study program.