Influence of Elastic Strains on the Adsorption Process in Porous Materials: An Experimental Approach

Abstract

The experimental results presented in this paper show the influence of the elastic deformation of porous solids on the adsorption process. With p + -type porous silicon formed on highly boron doped (100) Si single crystal, we can make identical porous layers, either supported by or detached from the substrate. The pores are perpendicular to the substrate. The adsorption isotherms corresponding to these two layers are distinct. In the region preceding capillary condensation, the adsorbed amount is lower for the membrane than for the supported layer and the hysteresis loop is observed at higher pressure. We attribute this phenomenon to different elastic strains undergone by the two layers during the adsorption process. For the supported layer, the planes perpendicular to the substrate are constrained to have the same interatomic spacing as that of the substrate so that the elastic deformation is unilateral, at an atomic scale, and along the pore axis. When the substrate is removed, tridimensional deformations occur and the porous system can find a new configuration for the solid atoms which decreases the free energy of the system adsorbate-solid. This results in a decrease of the adsorbed amount and in an increase of the condensation pressure. The isotherms for the supported porous layers shift toward that of the membrane when the layer thickness is increased from 30 to 100 µm. This is due to the relaxation of the stress exerted by the substrate as a result of the breaking of Si-Si bonds at the interface between the substrate and the porous layer. The membrane is the relaxed state of the supported layer.Author

Solid deformation induced by the adsorption of methane and methanol under sub- and supercritical conditions

“…We have found that methane and methanol adsorption can induce both pore shrinkage and expansion. The solvation pressure exerted by the adsorbate is a major reason for changes in pore dimension [12,13]. Solvation pressure itself can vary strongly with pore width, the nature of the adsorbate, and with adsorbate density and thus with temperature ( Fig.…”

“…More recent experimental work on the deformation of carbons during the adsorption of different gases has been reported by Fomkin and co-workers [6][7][8] and a dilatometric investigation of the deformation of carbon xerogels has been made by Balzer and co-workers [9] who concluded that micropores in the adsorbents made the most significant contribution to the expansion and contraction of these materials. Recognizing the significance of the effect of adsorption-induced deformation, more attention is paid on this phenomenon for various systems beside carbonaceous materials, such as porous glass [10], zeolites [11], silica gels [12], porous silicon [13,14] and metal-organic frameworks (MOFs) [15,16]. A review of the general area of adsorption deformation has been published by Tvardovski [17].…”

Modeling the Influence of Side Stream and Ink Bottle Structures on Adsorption/Desorption Dynamics of Fluids in Long Pores

“…2 This seems unlikely to us given that nitrogen is a wetting liquid for most surfaces due to the dominant contribution from dispersion forces and heterogeneity would typically enhance wetting in this case. It has also been suggested that the hysteresis in all these Psi systems can be explained by flexibility of the materials [8][9][10][11][12] but measurements of the effect of capillary condensation on the volume of Psi suggest a rather weak effect. 13 Understanding of this phenomenon may require comprehensive studies of not only thermodynamics, but also dynamics of fluids confined to disordered porous materials.…”

Hysteresis in modeling of poroelastic systems: Quasistatic equilibrium

“…It is traditional to get macroscopic hysteresis from the working of an assembly of microscopic hysteretic elements [18]. However, as is known in a different context [6], suspected in the current context [19], and as the models we have introduced show, there is another route to hysteresis. There are circumstances in which systems evolve among mesoscopic structures that are not easily reached from one another.…”