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Probing the Interfacial Behavior of Type IIIa Binary Mixtures Along the Three-Phase Line Employing Molecular Thermodynamics

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Departament de Ciència de Materials i Química Física & Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, 08028 Barcelona, Spain
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Departamento de Ingeniería Química, Universidad de Concepción POB 160–C, Concepción, Chile
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Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
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Author to whom correspondence should be addressed.
Molecules 2020, 25(7), 1499; https://doi.org/10.3390/molecules25071499
Received: 16 February 2020 / Revised: 18 March 2020 / Accepted: 20 March 2020 / Published: 25 March 2020
Interfacial properties such as interfacial profiles, surface activity, wetting transitions, and interfacial tensions along the three-phase line are described for a Type IIIa binary mixture. The methodological approach combines the square gradient theory coupled to the statistical associating fluid theory for Mie potentials of variable range, and coarse-grained molecular dynamics simulations using the same underlying potential. The water + n-hexane mixture at three-phase equilibrium is chosen as a benchmark test case. The results show that the use of the same molecular representation for both the theory and the simulations provides a complementary picture of the aforementioned mixture, with an excellent agreement between the molecular models and the available experimental data. Interfacial tension calculations are extended to temperatures where experimental data are not available. From these extrapolations, it is possible to infer a first order wetting transition at 347.2 K, where hexane starts to completely wet the water/vapor interface. Similarly, the upper critical end point is estimated at 486.3 K. Both results show a very good agreement to the available experimental information. The concentration profiles confirm the wetting behavior of n-hexane along with a strong positive surface activity that increases with temperature, contrasting the weak positive surface activity of water that decreases with temperature. View Full-Text
Keywords: square gradient theory; molecular dynamics; aqueous-hydrocarbon mixture; three-phase line interfacial properties; SAFT-VR Mie square gradient theory; molecular dynamics; aqueous-hydrocarbon mixture; three-phase line interfacial properties; SAFT-VR Mie
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Alonso, G.; Chaparro, G.; Cartes, M.; Müller, E.A.; Mejía, A. Probing the Interfacial Behavior of Type IIIa Binary Mixtures Along the Three-Phase Line Employing Molecular Thermodynamics. Molecules 2020, 25, 1499.

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