γ and dγ/dT measurements on aqueous solutions of 1,1-electrolytes

Measurements of the surface tension, γ, and its temperature derivative, dγ/dT, have been made by means of Wilhelmy slide techniques for dilute (≤ 1.5 m) aqueous solutions of NaCl, KCl, NaI, and KI. Using the data obtained, the thermodynamic surface zone properties have been evaluated for a surface phase containing only the water component. The results show that the distance of approach to the Gibbs dividing surface Σ(H2O) is approximately independent of the salt concentration and that it is smaller for the iodide ions than for the chloride ions due to differing modes of interaction with the surface zone water molecules. The possibilities of ion interaction with the uppermost layer of water molecules appear to be of particular importance and are strongly dependent on the polarization properties of the ions. Qualitative agreement is found with results of NMR quadrupole relaxation studies of anion interactions with the cage water layers formed at the hydrophobic cations in aqueous solutions of alkylammoniumhalides.