Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The validity of the Fowkes theory for the interaction of dispersion forces at interfaces was inspected for the system water-aliphatic hydrocarbons with 5 to 16 C atoms. The obtained results lead to the conclusion that the hydrocarbon molecules cannot lie in a parallel position or be randomly arranged on the surface but that orientation of molecules increases there the ration of CH₃ to CH₂ groups with respect to that in the bulk. This ratio is changed at the interface with water so that the surface free energy of the hydrocarbon, γ_H, rises to a higher value, γ’_H, which is effective in the interaction with water molecules. Not only the orientation of molecules depends on the adjoining phase and on the temperature but also the density of hydrocarbons on the surface of the liquid phase changes. It is lower than in the bulk and at the interface with water. Moreover, the volume occupied by the CH₃ group increases on the surface more than that of the CH₂ group. The dispersion component of the surface free energy of water, γ^d_W = 19.09 mJ/m², the non-dispersion component, γⁿ_W = 53.66 mJ/m², and the surface free energies of the CH₂ and CH₃ groups, γ(CH₂) = 32.94 mJ/m² and γ(CH₃) = 15.87 mJ/m², were determined at 20 °C. The dependence of these values on the temperature in the range 15-40 °C was also evaluated.