A perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state has been extended to include a crossover correction, based on White's work with renormalization-group (RG) theory, that accounts for the contributions of long-wavelength density fluctuations in the critical region. In the critical region, the improved crossover equation of state provides the correct nonclassical critical exponents. Away from the critical region, the crossover equation reduces to the original PC-SAFT equation, therefore maintaining the accuracy of PC-SAFT in this region. No modifications to the original PC-SAFT molecular parameters are necessary, therefore allowing for an accurate description of thermodynamic properties from the triple point to the critical point. Excellent agreement with vapor-liquid equilibrium experimental data for the n-alkane family is obtained inside and outside the critical region, and all critical constants T c , P c , and F c are calculated within their respective experimental errors. The extrapolative abilities of the RG parameters are demonstrated for higher molecular weight chains. Finally, the present results are contrasted with results from other groups using alternative interpretations of White's theory.

Second-order classical density functional theory is applied to assess the effect of surfactant properties on the interfacial structure and interfacial tension of a planar oil/water interface. Specifically the affect of the relative locations of the hydrophobic and hydrophilic portions, rigidity vs flexibility, and bond angle of the surfactant are investigated. It is found that bond angle and branching significantly affect the tendency of a surfactant to adsorb on the interface and the degree to which the interfacial tension is lowered.

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