Recent advances in classical density functional theory for associating and polyatomic molecules

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Aqueous solutions of alcohols are interesting because of their anomalous behavior that is believed to be due to the molecular structuring of water and alcohol around each other in solution. The interfacial structuring and properties are significant for application in alcohol purification processes and biomolecular structure. Here we study aqueous mixtures of short alcohols (methanol, ethanol, 1-propanol, and 2-propanol) at a hydrophobic surface using interfacial statistical associating fluid theory which is a perturbation density functional theory. The addition of a small amount of alcohol decreases the interfacial tension of water drastically. This trend in interfacial tension can be explained by the structure of water and alcohol next to the surface. The hydrophobic group of an added alcohol preferentially goes to the surface preserving the structure of water in the bulk. For a given bulk alcohol concentration, water mixed with the different alcohols has different interfacial tensions with propanol having a lower interfacial tension than methanol and ethanol. 2-propanol is not as effective in decreasing the interfacial tension as 1-propanol because it partitions poorly to the surface due to its larger excluded volume. But for a given surface alcohol mole fraction, all the alcohol mixtures give similar values for interfacial tension. For separation of alcohol from water, methods that take advantage of the high surface mole fraction of alcohol have advantages compared to separation using the vapor in equilibrium with a water-alcohol liquid. © 2013 AIP Publishing LLC.

Section: Introductionmentioning

confidence: 99%

Hydrophobic and hydrophilic interactions in aqueous mixtures of alcohols at a hydrophobic surface

Ballal

Chapman

2013

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“…A significant progress was the development of DFT models for representing the properties of polyatomic fluid on the basis of Wertheim's first order thermodynamic perturbation theory. [7][8][9][10][11] Compared to molecular simulation, most such DFT models accurately predict the microstructure of inhomogeneous fluid, but it is infeasible to use such models to represent properties of real substances due to the fact that most of these models were applied for model molecules with integer segment numbers. On the other hand, the bulk properties of fluids have been extensively studied in a) Electronic mail: xhlu@njut.edu.cn.…”

Section: Introductionmentioning

confidence: 99%

A hybrid perturbed-chain SAFT density functional theory for representing fluid behavior in nanopores

Shen

Lü

2013

A hybrid perturbed-chain SAFT density functional theory for representing fluid behavior in nanopores: Mixtures J. Chem. Phys. 139, 194705 (2013) A hybrid statistical mechanical model, which is fully consistent with the bulk perturbed-chain statistical associating fluid theory (PC-SAFT) in describing properties of fluids, was developed by coupling density functional theory with PC-SAFT for the description of the inhomogeneous behavior of real chain molecules in nanopores. In the developed model, the modified fundamental measure theory was used for the hard sphere contribution; the dispersion free energy functional was represented with weighted density approximation by averaging the density in the range of interaction, and the chain free energy functional from interfacial statistical associating fluid theory was used to account for the chain connectivity. Molecular simulation results of the density profile were compared with model prediction, and the considerable agreement reveals the reliability of the proposed model in representing the confined behaviors of chain molecules in an attractive slit. The developed model was further used to represent the adsorptions of methane and carbon dioxide on activated carbons, in which methane and carbon dioxide were modeled as chain molecules with the parameters taken from the bulk PC-SAFT, while the parameters of solid surface were obtained from the fitting of gas adsorption isotherms measured experimentally. The results show that the model can reliably reproduce the confined behaviors of physically existing substances in nanopores.

“…[1][2][3] A lot of methods have been used to represent the inhomogeneous behavior of confined fluids from experimental measurements, molecule simulations to theoretical models, and the classical density functional theory (DFT) in general provides reasonable description of inhomogeneous fluids with moderate computational cost. 4 A variety of DFT models have been developed to predict the properties of inhomogeneous simple atomic and complex fluids, and those based on Wertheim's first order thermodynamic perturbation theory (TPT1) are promising. [4][5][6][7] For example, Yu et al 8 developed a DFT based on Wertheim's TPT1 for chain conformation and bond orientation correlation function of hard-core multi-Yukawa chain fluids.…”

Section: Introductionmentioning

confidence: 99%

A hybrid perturbed-chain SAFT density functional theory for representing fluid behavior in nanopores: Mixtures

Shen

Öberg

et al. 2013

Nonequilibrium molecular dynamics simulation of transport and separation of gases in carbon nanopores. II. Binary and ternary mixtures and comparison with the experimental data J. Chem. Phys. 112, 910 (2000) The perturbed-chain statistical associating fluid theory (PC-SAFT) density functional theory developed in our previous work was extended to the description of inhomogeneous confined behavior in nanopores for mixtures. In the developed model, the modified fundamental measure theory and the weighted density approximation were used to represent the hard-sphere and dispersion free energy functionals, respectively, and the chain free energy functional from interfacial statistical associating fluid theory was used to account for the chain connectivity. The developed model was verified by comparing the model prediction with molecular simulation results, and the agreement reveals the reliability of the proposed model in representing the confined behaviors of chain mixtures in nanopores. The developed model was further used to predict the adsorption of methane-carbon dioxide mixtures on activated carbons, in which the parameters of methane and carbon dioxide were taken from the bulk PC-SAFT and those for solid surface were determined from the fitting to the pure-gas adsorption isotherms measured experimentally. The comparison of the model prediction with the available experimental data of mixed-gas adsorption isotherms shows that the model can reliably reproduce the confined behaviors of physically existing mixtures in nanopores. © 2013 AIP Publishing LLC.