Charge generation at mineral-electrolyte interfaces: from microscopic ion adsorption to local viscosity enhancement and macroscopic wettability alteration

Mugele, F. G. (Invited speaker)

Activity: Talk or presentationInvited talk

Description

The generation of charge at the interface between oxides surfaces and aqueous electrolytes is a complex process that involves protonation/deprotonation reactions, adsorption and desorption of ions as well as hydration and dehydration processes. In this lecture, I will discuss insights from Atomic Force Microscopy experiments on the surface charge of various mineral surface (silica, gibbsite, mica) upon immersion into aqueous electrolytes of variable composition. I will show in particular how the majority of the intrinsic charge density of such surfaces is typically screened within the Stern layer, leaving only a fraction of the available surface sites effectively charged if probed at colloidal scale distances of a few nanometers. This charge compensation process involves both strongly adsorbed counterions as well as hydroxyl and hydronium ions. For the specific case of silica-electrolyte interfaces, the resulting double layer structure gives rise to an enhanced effective viscosity within a few nanometers from the surface at elevated pH. For mica-electrolyte interfaces, the adsorption of divalent cations leads to charge reversal and the adsorption of heavy alkali cations (Rb^+,Ca^+) disrupts the intrinsic layers hydration structure of the solid. Both processes have important consequences for the macroscopic wettability of the interfaces: in contrast to pure water, which completely wets mica in ambient oil, solutions of strongly adsorbing cations display a transition from complete to partial wetting with macroscopic contact angles exceeding 〖10〗^°beyond a certain threshold concentration. The altered chemical composition of the surface also promotes the secondary adsorption of polar components if dissolved in the oil. This leads to autophobing with contact angles up to 〖70〗^° and self-propelled motion of electrolyte droplets. The latter process is driven by the deposition of a self-assembled monolayer of surfactant at the solid surface and is believed to play an important role in technological processes such as the recovery of oil from fossil reservoirs.
Period22 Oct 2018 - 25 Oct 2018
Held atLiquids@Interfaces 2018
Event typeConference
LocationBordeaux, France
Degree of RecognitionInternational