A Poromechanical Model for Sorption Hysteresis in Nanoporous Polymers

Abstract

Sorption hysteresis in nanoporous polymer is an intriguing phenomenon that involves coupling between sorption and deformation. Based on the mechanism revealed at the microscopic level using molecular simulation, a poromechanical model is developed capturing all relevant physics and yielding a quantitative description. In this model, the coupling between sorption and deformation is described by a poromechanics framework. More in detail, an upscaling process from the molecular mechanism is implemented to model the hysteresis through the state change of each element upon deformation. We provide two solutions of the model, a numerical one based on the finite element method and an analytical one based on uniform strain assumption. The results from both solutions agree well with the molecular simulation and experimental results, therefore capturing and describing adequately sorption hysteresis. The developed model illustrates that water forms different structural distributions upon adsorption and desorption. A parametric study shows that sorption hysteresis is influenced by material properties. We find that a softer material with stronger adsorbent-adsorbate interaction tends to exhibit more profound sorption hysteresis. The developed model, which relies on the concepts of sorption-deformation coupling and multi-scale modeling from atomistic simulations to domain dependent theory, paves the way for a new direction of modeling sorption hysteresis.

Models of adsorption-induced deformation: ordered materials and beyond

“…Namely, it smooths the abrupt condensation/evaporation transitions similarly to adsorption isotherms (see figure 11(b)), which allows one to describe experimental data [36,85] better. A similar idea of strain pore size coupling was recently applied in the study of sorption hysteresis in nanoporous polymers [86]. The authors used the idea that pores exposed to AID affect their neighbors.…”

Kerogen Differential Swelling during CO2-CH4 Adsorption: Mechanism and Significance

“…Sui and Yao quantified kerogen swelling using the extended poromechanical model and condensed-phase optimized molecular potential for atomistic simulation studies (COMPASS) force field. Then, Chen et al advanced the poromechanical model and found that swelling of the coal matrix is more significant at high pressures than at low pressures. Wang et al quantified the volumetric strain of kerogen at different pressures (1–30 MPa) at temperatures of 298–388 K and demonstrated the opposite effect of adsorption and mechanical compression on the volumetric strain behaviors.…”

Deformation of Nanoporous Materials in the Process of Binary Adsorption: Methane Displacement by Carbon Dioxide from Coal

“…Although the effects of adsorption-induced deformation and their practical importance are well documented for geosorbents and other nanoporous solids, most theoretical and experimental efforts are limited to single component adsorption. There are various approaches for modeling multicomponent adsorption on carbons, zeolites, and MOFs that do not take into account the adsorbent deformation. − The density functional theory (DFT) and Monte Carlo (MC) molecular simulation models were suggested to study adsorption-induced deformation processes on the atomistic level. , Adsorption-induced transformations in MOFs have received special attention. − ,− Several theoretical approaches have been suggested to extend the macroscopic poromechanics to nanoporous adsorbents and account for the adsorption effects. − It is worth noting the works − aimed at modeling secondary methane recovery and CO 2 sequestration on coal. The progress in theoretical modeling is hindered by a lack of systematic experimental studies of adsorbent deformation during multicomponent adsorption.…”