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O: Fachverband Oberflächenphysik

O 18: Solid-liquid Interfaces II

O 18.6: Vortrag

Montag, 31. März 2014, 17:15–17:30, WIL A317

Wetting Transition in a solid/water/oil system mediated by ion and surfactant -adsorption induced interface interactions — •Bijoyendra Bera, Igor Sîretanu, Michèl H.G. Duits, Martien A. Cohen-Stuart, Dirk van den Ende, and Frieder Mugele — Physics of Complex Fluids (PCF) Group, TNW, University of Twente, Enschede, The Netherlands

Enhanced oil recovery (EOR) processes rely upon wettability alteration in sandstone rock (silica and clay materials). In this study, by changing the salt (NaCl or CaCl₂), concentration (1 mM to 1000 mM) and pH, we observe wetting transition on mica in an oil (n-Decane) phase. At all pH and concentration of NaCl, contact angles below macroscopic detection limit (around 1.5⁰) are observed, implying complete wetting. For CaCl₂, we observe finite contact angles (up to 10⁰) above a critical concentration of 50 mM. When we add polar amphiphilic molecules (stearic acid) in n-Decane, this wetting transition is more pronounced since for CaCl₂ solution, contact angles are as high as 70⁰. In presence of stearic acid, dynamic effects such as autophobing and self-propelling of drops on mica are also observed.

We explain such wetting transition with an ion-adsorption model, causing surface charge reversal at mica/water interface for divalent cations. This proposition is supported with experimental calculations of zeta potential. Based on these values, we calculate surface charge and subsequently, the interaction potential between mica/water and oil/water interfaces. The minimum of this potential corresponds to the film thickness of aqueous phase, which we confirm with ellipsometry.