Crown-ethers
have recently been used to assemble porous liquids
(PLs), which are liquids with permanent porosity formed by mixing
bulky solvent molecules (e.g., 15-crown-5 ether) with solvent-inaccessible
organic cages. PLs and crown-ethers belong to a novel class of materials,
which can potentially be used for gas separation and storage, but
their performance for this purpose needs to be assessed thoroughly.
Here, we use molecular simulations to study the gas separation performance
of crown-ethers as the solvent of porous liquids. The TraPPE force
field for linear ether molecules has been adjusted by fitting a new
set of torsional potentials to accurately describe cyclic crown-ether
molecules. Molecular dynamics (MD) simulations have been used to compute
densities, shear viscosities, and self-diffusion coefficients of 12-crown-4,
15-crown-5, and 18-crown-6 ethers. In addition, Monte Carlo (MC) simulations
have been used to compute the solubility of the gases CO2, CH4, and N2 in 12-crown-4 and 15-crown-5
ether. The computed properties are compared with available experimental
data of crown-ethers and their linear counterparts, i.e., polyethylene
glycol dimethyl ethers.