THE INFLUENCE OF OLEATE ADSORPTION AT THE FLUORITE WATER INTERFACE ONFLUORITE SURFACE FREE-ENERGY

Contact-angle measurements for water, glycerol, formamide, di-iodometh ane and bromoform on fluorite plates covered with a film of oleate are made. Using the contact-angle values, the Lifshitz-van der Waals comp onent and the electron-acceptor parameter of the surface free energy o f the fluorite/oleate film are calculated. On the basis of the contact -angle measurements and the calculations done, it is found that at low equilibrium oleate concentration the surface free energy of the fluor ite/oleate film comes close to the value for paraffin, however at high oleate concentration, the surface of the fluorite/oleate film can int eract with the adherent phase not only by Lifshitz-van der Waals force s but also by acid-base forces. It results from a hydration process wh ich takes place at the highest sodium oleate concentrations. It is sta ted that the considerable decrease of the fluorite/oleate-film-water i nterfacial free energy at oleate species concentration higher than 87. 1 mg/dm3 can also result from electrostatic interactions across the in terface.