MICROELECTROPHORESIS OF SILICA IN MIXED-SOLVENTS OF LOW DIELECTRIC-CONSTANT

Electrophoretic mobilities of monodisperse, spherical silica particles (300 and 700 nm in diameter) in dioxane/water mixtures have been studied at 1:1 electrolyte concentrations over the range 10(-6)-10(-4) mol dm-3. At dioxane contents of 80-95% (w/w), the potentials are negative in KOH solutions and positive at sufficiently high HCl concentrations. The addition of KCl in increasing amounts leads to a decrease in the mobility of silica in 80% dioxane/water, while at 90 and 95% dioxane, the charge reversal from negative to positive takes place. An analogous effect is observed with RbCl and CsCl, but not with LiCl and NaCl. At still higher dioxane concentrations (> 97.5%), the mobilities approach zero within the experimental error at the studied range of electrolyte concentrations.