(510b) Elasticity of Simple Fluids Confined in Nanopores

Predicting the behavior of fluids in porous media is crucial for hydrocarbons recovery and carbon sequestration in geological formations. Fluid transport in porous medium depends on the fluid elasticity (bulk modulus). Substantial growth of interest in shale gas recovery drew attention to fluids transport in geological media with pores in the nanometer range. Since nanoconfinement is known to significantly affect thermodynamic properties of fluids, one can expect its influence on fluid elasticity as well. Indeed, recently Schappert and Pelster proposed a method to determine the elasticity of the fluid confined in nanopores from ultrasonic experiments [1]. Their findings showed that the bulk modulus of liquid argon confined in Vycor glass is affected by high solvation pressure in the pores, which is also known to cause adsorption-induced deformation [2].

Here we use the Quenched Solid Density Functional Theory (QSDFT) method [3] to calculate the bulk modulus of nanoconfined fluid. QSDFT accurately predicts thermodynamic properties of confined fluids, and is widely used for characterization of porous materials [4]. However, QSDFT has not been employed to calculate the derivative properties, including compressibility which determines the bulk modulus.

Our calculations showed that QSDFT method is capable of predicting the bulk modulus of simple fluids confined in nanopores. Our results showed that the elasticity of confined fluid changes with the solvation pressure in the pore, which is in line with the experimental observations by Schappert and Pelster. Additionally we showed that the bulk modulus of the confined fluid increases with the degree of confinement – fluids adsorbed in smaller pores are noticeably stiffer than those adsorbed in the large ones. These effects need to be taken into account in large scale models for predicting the fluid flow in nanoporous geological formations such as shale.

References

[1] K. Schappert, R. Pelster, Influence of the laplace pressure on the elasticity of argon in nanopores, EPL (Europhysics Letters) 105 (5) (2014) 56001.
[2] G. Y. Gor, A. V. Neimark, Adsorption-induced deformation of mesoporous solids, Langmuir 26 (16) (2010) 13021–13027.
[3] P. I. Ravikovitch, A. V. Neimark, Density functional theory model of adsorption on amorphous and microporous silica materials, Langmuir 22 (26) (2006) 11171–11179.
[4] J. Landers, G. Y. Gor, A. V. Neimark, Density functional theory methods for characterization of porous materials, Colloids and Surfaces A: Physicochemical and Engineering Aspects 437 (2013) 3–32.