Henry's law, surface tension, and surface adsorption in dilutebinary mixtures

摘要

Equilibrium properties of dilute binary fluid mixtures are studied in two-phase states on the basis ofa Helmholtz free energy including the gradient free energy. The solute partitioning between gas andliquid (Henry's law) and the surface tension change A y are discussed. A derivation of the Gibbs lawΔγ=-–TT is given with Γ being the surface adsorption. Calculated quantities include the derivativesdT_c/ dXanddp_c/ dXof the critical temperature and pressure with respect to the solute molar fractionX and the temperature-derivative (γ/T)_(cx,p)of the surface tension at fixed pressurepon thecoexistence surface. Here (γ/ T)_(cx,p)can be both positive and negative, depending on the solutemolecular size and the solute-solvent interaction, and diverges on the azeptropic line. Explicitexpressions are given for all these quantities in the van der Waals model.