Effect of Amphiphile Hydrophobicity on Wetting Behaviors of Ternary Water + Oil + Amphiphile Mixtures: A Density Functional Theory Approach

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In this study, the statistical associating fluid theory (SAFT) combined with the density functional theory (DFT) was applied to explore the phase and wetting behavior of ternary water + oil + amphiphile mixtures. It is well understood that this type of mixture exhibits a three-liquid-phase coexisting under the condition of certain temperature, pressure and concentration ranges. The Helmholtz free energy model of SAFT successfully delineates the phase behavior of the water + oil + amphiphile ternary mixture. The DFT was further applied to calculate the interfacial tensions of the coexisting phases. The wetting behavior of the amphiphile-rich phase at the interface separating the oil-rich and aqueous phases was then determined according to whether the interfacial tensions obey either Antonow's rule or Neumann inequality. The occurrence of wetting transitions was systematically explored while the system is brought to its critical end point. A parameter R was proposed to emulate the amphiphile hydrophobicity....