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. 2017 Sep 7;121(35):8367-8376.
doi: 10.1021/acs.jpcb.7b06547. Epub 2017 Aug 25.

Thermodynamic and Transport Properties of Crown-Ethers: Force Field Development and Molecular Simulations

Seyed Hossein Jamali  1 , Mahinder Ramdin  1 , Tim M Becker  1 , Shwet Kumar Rinwa  1 , Wim Buijs  1 , Thijs J H Vlugt  1
Affiliations

Thermodynamic and Transport Properties of Crown-Ethers: Force Field Development and Molecular Simulations

Seyed Hossein Jamali et al. J Phys Chem B. .

Abstract

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.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Schematic representation of the studied crown-ethers.
Figure 2
Figure 2
Fitted torsional potential (Table 1) compared to the torsional potential of the linear ether TraPPE torsional force field (red dashed lines).
Figure 3
Figure 3
Comparison between torsional potentials computed for all dihedral angles of the first 10 conformers of 12-crown-4 (red squares), 15-crown-5 (blue circles), and 18-crown-6 (green diamonds) optimized using the DFT calculations and the newly fitted torsional potential.
Figure 4
Figure 4
Relative error in calculated densities of 12-crown-4 (red), 15-crown-5 (blue), and 18-crown-6 (green) at different temperatures based on the linear ether TraPPE (open symbols) and the refined TraPPE (closed symbols) force fields. The simulation results are available in the Supporting Information.
Figure 5
Figure 5
Self-diffusion coefficient of 12-crown-4 at 363 K for different system sizes. Blue circles represent self-diffusion coefficients directly computed from MD results and red squares are the corrected self-diffusion coefficients with the Yeh and Hummer correction (eq 3). The blue dashed line is fitted to the MD simulations and the green line is the extrapolated self-diffusion coefficient in the thermodynamic limit.
Figure 6
Figure 6
Viscosity of the 12-crown-4, 15-crown-5, and 18-crown-6 as functions of temperature based on the linear ether TraPPE (open symbols) and the refined TraPPE (closed symbols) force fields. Green lines represent experimental data. The simulation results are available in the Supporting Information.
Figure 7
Figure 7
Self-diffusion of the 12-crown-4, 15-crown-5, and 18-crown-6 at different temperatures, computed from the linear ether TraPPE (open symbols) and the refined TraPPE (closed symbols) force fields. Experimental data are shown with green lines. The linear ether TraPPE force field predicts a solid system for 12-crown-4 for the shown temperatures. The self-diffusion coefficients without and with the inclusion of the YH correction are shown with blue circles/dashed lines and the red squares/dashed lines, respectively. The simulation results are available in the Supporting Information.
Figure 8
Figure 8
Solubility of CO2 (red squares/lines), CH4 (blue circles/lines), and N2 (green diamonds/lines) in 12-crown-4 (closed symbols/solid lines) and 15-crown-5 (open symbols/dashed lines) at 333 K. The results are fitted to eq 4, whose parameters are provided in Table 2. The simulation results are available in the Supporting Information.
Figure 9
Figure 9
Henry coefficients of CO2 (red squares/lines), CH4 (blue circles/lines), and N2 (green diamonds/lines) in 12-crown-4 (closed symbols/solid lines) and 15-crown-5 (open symbols/dashed lines) at different temperatures. The lines are fitted to eq 10 and the fitted parameters are listed in Table 4.
Figure 10
Figure 10
Viscosity and self-diffusion coefficient of CO2 in the mixtures of 9%-mole CO2 and 12-crown-4 (red squares/line), 15-crown-5 (blue circles/line), and 18-crown-6 (green diamonds/line) at different temperatures. The lines are fitted to eq 4 and the parameters are available in Table 5. The simulation results are available in the Supporting Information.
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