Quantifying the effect of polar interactions on the behavior of binary mixtures: Phase, interfacial, and excess properties

Abstract

In this work, polar soft-Statistical Associating Fluid Theory (SAFT) was used in a systematic manner to quantify the influence of polar interactions on the phase equilibria, interfacial, and excess properties of binary mixtures. The theory was first validated with available molecular simulation data and then used to isolate the effect of polar interactions on the thermodynamic behavior of the mixtures by fixing the polar moment of one component while changing the polar moment of the second component from non-polar to either highly dipolar or quadrupolar, examining 15 different binary mixtures. It was determined that the type and magnitude of polar interactions have direct implications on the vapor–liquid equilibria (VLE), resulting in azeotropy for systems of either dipolar or quadrupolar fluids when mixed with non-polar or low polar strength fluids, while increasing the polar strength of one component shifts the VLE to be more ideal. Additionally, excess properties and interfacial properties such as interfacial tension, density profiles, and relative adsorption at the interface were also examined, establishing distinct enrichment in the case of mixtures with highly quadrupolar fluids. Finally, polar soft-SAFT was applied to describe the thermodynamic behavior of binary mixtures of experimental systems exhibiting various intermolecular interactions (non-polar and polar), not only demonstrating high accuracy and robustness through agreement with experimental data but also providing insights into the effect of polarity on the interfacial properties of the studied mixtures. This work proves the value of having an accurate theory for isolating the effect of polarity, especially for the design of ad hoc polar solvents.

Searching for Sustainable Refrigerants by Bridging Molecular Modeling with Machine Learning

“…To ensure a robust model and minimized fitting to data, the dipole moment was fixed to the experimental value in a vacuum, and the fraction of dipolar segments was determined a priori based on a physical argument highlighted in previous contributions. 63 , 68 − 70 With that, only the three remaining parameters ( i.e. , m , σ, ε) were simultaneously fitted to limited data sets including each refrigerant’s liquid density and vapor pressure.…”

Assessment of Low Global Warming Potential Refrigerants for Drop-In Replacement by Connecting their Molecular Features to Their Performance

“…The reader is referred to the original contributions for additional details on the expressions of soft-SAFT and its polar extension. 46 , 47 , 66 , 71 − 73 …”

“…Such explicit treatment is paramount as it ensures high predictive accuracy in modeling pure polar fluid properties and their multicomponent mixtures as demonstrated for other polar fluids in our earlier contributions. 46 , 47 , 66 , 73 It should be noted that the association term was not included, as the dipolar nature of these refrigerants is far more influential on their thermodynamic behavior.…”

“…Lastly, the polar term ( a polar ) explicitly accounts for the contribution from multipolar interactions such as a permanent dipole or quadrupole. The reader is referred to the original contributions for additional details on the expressions of soft-SAFT and its polar extension. ,,,− …”

“…These models have rigorous physical basis from statistical mechanics, enabling them to accurately capture the effect of intermolecular interactions (i.e., dispersive, associating, polar) on macrolevel phenomena. This is an added edge over conventional EoSs, that are incapable of explicitly modeling polar interactions governing the behavior of third and fourth generation refrigerants and other green substances of polar nature. − The adoption of SAFT-based models as a central pillar for screening tools has been steadily growing, − holding the promise of similar success when applied to screening alternative eco-friendly refrigerants as drop-in replacements under the same operating conditions and technical criteria. This is fueled by the demonstrated success of our group in accurately modeling the holistic thermodynamic behavior of third and fourth generation refrigerants. − On another front, the physical basis of SAFT-based models can enable the extraction of microlevel tendencies linked with observable physicochemical properties and technical performance.…”