Suk Yung Oh

Phase equilibrium calculations of ternary liquid mixtures with binary interaction parameters and molecular size parameters determined from molecular dynamics.

The method presented in this paper was developed to predict liquid-liquid equilibria in ternary liquid mixtures by using a combination of a thermodynamic model and molecular dynamics simulations. In general, common classical thermodynamic models have many parameters which are determined by fitting a model with experimental data. This proposed method, however, provides a simple procedure for calculating liquid-liquid equilibria utilizing binary interaction parameters and molecular size parameters determined from molecular dynamics simulations. This method was applied to mixtures containing water, hydrocarbons, alcohols, chlorides, ketones, acids, and other organic liquids over various temperature ranges. The predicted results agree well with the experimental data without the use of adjustable parameters.

Understanding liquid mixture phase miscibility via pair energy parameter behaviors with respect to temperatures determined from molecular simulations.

The miscibility behaviors of binary liquid mixtures were studied by a combination of molecular simulations and thermodynamic theories. Pairwise interaction parameters were obtained from molecular simulations that accounted for the effect of temperature. From a thermodynamic perspective, different types of liquid-liquid equilibrium (LLE) and different degrees of miscibility can be expressed in terms of energy behaviors with respect to temperature. Our simulation results proved this viewpoint by showing a correspondence between the simulation results and experimental observations. To describe phase diagrams, thermodynamic modeling is presented using the energy parameters obtained from the simulations. Correlations are needed to correct size mismatches between the simulations and the thermodynamic model. Using this method, not only the upper critical solution temperature (UCST) but also the closed-loop miscibility phase diagrams could be calculated without requiring additional parameters for specific interactions. The utility of this method is demonstrated for mixtures containing water, hydrocarbon, alcohols, aldehydes, ketones, chlorides, amines, nitriles, sulfides, and other organic liquids in various temperature ranges. The method presented in this paper can facilitate the understanding of the miscibilities in binary liquid mixtures from the viewpoint of thermal energy behaviors.

Molecular simulations and thermodynamic modeling for closed-loop phase miscibility of aqueous PEO solutions

AbstractClosed-loop (CL) phase miscibility behavior of aqueous poly(ethylene oxide) (PEO) solutions was studied by means of molecular simulations and thermodynamic modeling. We first have performed a molecular dynamics (MD) simulation of PEO-water solutions. A careful MD procedure is established based on the corresponding experiments so that the correct surrounding conditions of the simulated cells are constructed. We computed radial distribution functions, number of hydrogen bonds, energy of mixing, mean-squared displacements, and radius of gyration with respect to the temperature. We found that hydrogen bonds between PEO and water decrease more rapidly than those of water and water with increasing temperature, indicating lower critical solution temperature (LCST) behavior. In the heterogeneous phase temperature range, both mixing energy and radius of gyration showed lower values than those of the homogenous phase, which correspond well with the CL type miscibility behavior. Secondly, a thermodynamic modeling technique is presented to quantitatively describe phase equilibrium, using the energy parameters obtained from molecular simulations. We calculated the CL temperature-composition phase diagram of PEO-water solutions using this modeling method and compared it with the experimental data. The calculated results are also consistent with the experimental data using only one scaling parameter. CL phase miscibility of PEO-water solutions is understood successfully by these two types of studies.

Group contribution method for group contribution method for estimation of vapor liquid equilibria in polymer solutions

This study introduces a specified group-contribution method for predicting the phase equilibria in polymer solutions. The method is based on a modified double lattice model developed previously. The proposed model includes a combinatorial energy contribution that is responsible for the revised Flory-Huggins entropy of mixing, the van der Waals energy contribution from dispersion, a polar force and specific energy contribution. Using the group-interaction parameters obtained from data reduction, the solvent activities for a large variety of mixtures of polymers and solvents over a wide range of temperatures can be predicted with good accuracy. This method is simple but provides improved predictions compared to those of the other group contribution methods.