ORGANIC DROPLETS AT AN ELECTRIFIED INTERFACE - CRITICAL POTENTIALS OF WETTING MEASURED BY POLAROGRAPHY

Critical wetting potentials of a dropping mercury electrode immersed in aqueous dispersions of organic liquids represent well-defined and characteristic values, that might offer predictions of interpolative nature for interactions of organic particles in the aquatic environment and a framework for investigation of fast wetting transients. The polarographic method is based on measurement of charging current caused by displacement of surface charge due to attachment and spreading of organic droplets (micrometer size range) at the aqueous-mercury interface. Dispersion of hexadecane in 0.1 M NaF aqueous solution was used as a model system. Excellent agreement was obtained between critical interfacial tension of wetting (418.2 mJ m-2 at negatively and 418.9 mJ m-2 at positively charged electrodes) determined from critical potentials and prediction based on the Good-Girifalco-Fowkes equation for the mercury-water-hexadecane system (418.26 mJ m-2). Experimental values for unsaturated hydrocarbons were significantly lower: 414 mJ m-2 for 1-octadecene and 400 mJ m-2 for squalene.