Preferential adsorption in a near-critical binary fluid mixture as analyzed in the framework of the non-random two-liquid model.

We consider a binary fluid mixture, which lies in the one-phase region near the demixing critical point. Short-range interactions between the mixture components and a solid surface in contact with the mixture can make the mixture composition inhomogeneous significantly near the surface. This inhomogeneity has been shown to cause various phenomena by using the renormalized local functional theory. In its free-energy density, the order-parameter field is coarse-grained without rescaled and only the most singular part is specified. In the present study, on the basis of the crossover theory, we introduce a square-gradient term to the free-energy density of the extended non-random two-liquid model, which includes more than the most singular part. Thanks to similarity between the renormalized local functional theory and the crossover theory, the relationship between the two free-energy densities can be clarified. Supposing a mixture of nitroethane and 3-methylpentane and a mixture of 2,6-lutidine and water, we use the proposed free-energy density to calculate the inhomogeneous composition profile numerically. The free-energy density also enables us to calculate excess densities of entropy and enthalpy, unlike that of the renormalized local functional theory. We also find that the magnitude of the thermal force density, which is induced by a temperature gradient to cause flow in thermoosmosis, can depend on the calculation procedures significantly. [ABSTRACT FROM AUTHOR]

Copyright of Fluid Phase Equilibria is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)