Elastocapillarity in nanopores: Sorption strain from the actions of surface tension and surface stress

Document Type

Article

Publication Date

8-31-2018

Abstract

Adsorption-induced deformation of porous materials is the generation of strains in a solid due to its interaction with adsorbing fluids. The theoretical description of adsorption-induced deformation often relies on the so-called solvation pressure, the normal component of a pressure tensor in the liquid adsorbed in the pore. Recent measurements of adsorption-induced strains in two dimensions require a description that allows for the deformation to be anisotropic. Here, we present such a description. We refrain from using the solvation pressure concept and instead base the discussion on a phenomenological description of coupled mechanics and adsorption that has well-established links to continuum mechanics. We find that our approach captures all relevant features of anisotropic sorption strain; the approach thus provides a useful alternative to the solvation pressure concept. We derive analytical expressions for the stress-strain relations in a model porous material with an array of parallel channel-like pores of high aspect ratio (length/width). These relations include separate terms from the liquid pressure, from the surface stress at the liquid-solid interface, and from a spreading tension at the solid-liquid-vapor triple line. Surface stress and liquid pressure contribute to the strains along and normal to the pore axis in a qualitatively different manner. The underlying discussion of capillary forces sheds light on the variation of the surface stress during adsorption and capillary condensation.

Identifier

85051696920 (Scopus)

Publication Title

Physical Review Materials

External Full Text Location

https://doi.org/10.1103/PhysRevMaterials.2.086002

e-ISSN

24759953

Issue

8

Volume

2

Grant

SFB 986

Fund Ref

Deutsche Forschungsgemeinschaft

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