Sprecher
Beschreibung
Water dewetting generates static electricity. We studied the charging of polymer slides and metal electrode supported polymer films withdrawn vertically from a pool of aqueous solutions. For pure water, charging was negative and surface charge densities increased with the speed of dewetting, which we explain by the entrainment of nanometer-sized water droplets charged by unbalanced adsorbed electric double-layer ions. At low salinity c ≲ 10 μM, charging was proportional to electrokinetic interfacial charge densities: Charge polarity was inversed to positive for a cationic surfactant, a salt with a highly positively charged cation, and for a strong acid at approximately pH 4. We furthermore show that the surface charge distribution, imaged by charged toner powders and measured microscopically by Kelvin probe force microscopy, is a record of the dewetting process that provides spatial and kinetic information about the three-phase contact line motion.