The thermodynamics of multilayer adsorption at S/L interfaces in binary mixtures was investigated, applying the lattice model (Bragg-Williams and the "nearest neighbour" approximations). We suggest a method to partition the thermodynamic potential functions according to monomolecular sublayers. The calculations verified our earlier hypothesis that the main part of the free energy of adsorption, Δ21F, belongs to the first sublayer. In the case of thick adsorption layers it was observed that the internal energy and the entropy terms of the 2nd and higher sublayers compensate each other. The equivalent layer thickness depends first of all on the demixing tendency of the given liquid mixture and the role of the surface polarity seems to be less important. Inflexion points of the Δ21F vs. x1 and Δ21U vs. x1 functions were observed at the maximum value of the layer thickness. This result of the theoretical analysis allows us to emphasize the importance of the calorimetric measurements in the course of the experimental investigation of multilayer adsorption.
|Journal||Magyar Kemiai Folyoirat, Kemiai Kozlemenyek|
|Publication status||Published - Nov 1 2001|
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