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BP: Fachverband Biologische Physik

BP 38: Electrolytes at Interfaces - Stern Layer (focus session, joint CPP/BP/O)

BP 38.4: Vortrag

Mittwoch, 18. März 2015, 16:00–16:15, C 130

Ion adsorption-induced wetting transition in oil-water-mineral systems — •Frieder Mugele, Bijoy Bera, Andrea Cavalli, Igor Siretanu, Armando Maestro, Dirk van den Ende, Michel Duits, and Martien Cohen-Stuart — University of Twente, MESA+ Institute for Nanotechnology, Physics of Complex Fluids, Enschede, The Netherlands

The relative wettability of oil and water on solid surfaces is crucial to many environmental and technological processes including soil contamination/remediation, oil-water separation, and oil recovery. Good wettability of one fluid generally implies strong retention of that fluid in a porous solid matrix and simultaneously easy displacement of the other one. Here, we demonstrate that the contact angle of aqueous solutions of common chloride salts on mica in ambient oil displays a transition from near zero to finite contact angles up to 10° upon replacing monovalent Na+ and K+ cations in the aqueous phase by divalent Ca2+ and Mg2+ at neutral to elevated pH. This wetting transition is driven by electrostatic forces and originates from charge reversal of the mica-water interface upon adsorption of divalent cations. The ion-induced wettability alteration is synergistically enhanced by small amounts of polar molecules, stearic acid, added to the ambient oil, leading to water contact angles up to 70°.