(746g) Modeling Compressibility of Confined Fluids Via Molecular Simulation and Equation of State

Many properties of fluids are affected by nanoconfinement, and compressibility is not an exception. The knowledge of elastic properties of fluids confined in nanopores is important for correct predictions of fluid flow and wave propagation in nanoporous media. The compressibility of a confined fluid depends on the solvation pressure in the pore and the degree of confinement or poresize. [1-3] For fluids in macroporous media, many bulk equations of state (EOSs) can provide reliable predictions of all thermodynamic properties, including compressibility. However, fluids in nanopores have altered thermodynamic properties which do not follow bulk EOSs. In recent years, a number of attempts of generalization of conventional EOSs for confined fluid have been made [4-6]. For example, Travalloni and coauthors have shown that modified cubic equations of state can be used to predict adsorption of pure fluids and mixtures in nanopores [4]. Their work, however, did not discuss the predictions for compressibility.

Here we conduct grand canonical Monte Carlo and molecular dynamics simulations to calculate the elastic properties of the confined fluids. We compare predictions of various properties including the elastic moduli of the confined fluids obtained from our molecular simulations to the calculations from the EOSs from reference [4]. We found reasonable agreement between the modified Peng-Robinson EOS and molecular simulation predictions. These results enable improved models and interpreting ultrasonic experiments by shedding light on how fluids behave in nanoconfinement.

[1] G. Y. Gor, Langmuir, 30(45), 13564 (2014)

[2] G. Y. Gor, D. W. Siderius, V. K. Shen, N. Bernstein, J. Chem. Phys. 145(16), 164505 (2016)

[3] C. D. Dobrzanski, M. A. Maximov, G. Y. Gor, J. Chem. Phys. 148, 054503 (2018)

[4] G. D. Barbosa, M. L. D’Lima, S. M. H. Daghash, M. Castier, F. W. Tavares, L. Travalloni, Chem. Eng. Sci., 184, 52 (2018)

[5] G. J. Zarragoicoechea, V. A. Kuz, Phys. Rev. E., 65, 021110 (2002)

[6] A. W. Islam, T. W. Patzek, A. Y. Sun, J. Nat. Gas. Sci. Eng., 25, 134 (2015)