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

这个早期概念探索性研究（EAGER）项目的目的是阐明微孔中受阻吸附层的吸附滞后的原因，这一问题60多年来一直没有得到根本解释。研究了两种机制。一种是在非均匀孔隙填充或排空过程中，由于失配分离压力的非唯一性，当孔隙厚度通过单层厚度的整数倍时，由一系列的断裂不稳定性组成。第二种是在部分填充层内的分子聚结或分离，通过spinodal分解（均匀填充的线性不稳定性）或缺陷或孔洞处的成核。在宏观尺度上，这两种机制都导致了许多平行孔隙的非均质填充或排空，以及热力学计算的分离压力的巨大变化。这些变化是干燥蠕变和收缩的任何物理理论的重要组成部分。另一个目标是通过吸附测试确定孔径分布和内表面积，第三个目标是预测流体通过微孔固体的输送。微孔固体的吸附滞后控制着微尺度应力，这些应力控制着微孔内和微孔周围的蠕变和非弹性变形以及吸附过程中的能量耗散。吸附循环所耗散的能量会造成材料的损坏。这些现象对于预测各种混凝土结构的破坏和蠕变、煤层的甲烷释放、岩石的固气能力、页岩的气体释放等具有重要意义。将编写一门包含提案主题的课程。这项工作将有助于本科生和研究生的教育。本科生将参与一个特殊目的的勤工俭学计划。

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.