Pickering emulsions stabilized by stacked catanionic micro-crystals controlled by charge regulation

Abstract

In this paper the mechanism behind the stabilization of Pickering emulsions by stacked catanionic micro-crystals is described. A temperature-quench of mixtures of oppositely charged surfactants (catanionics) and tetradecane from above the chain melting temperature to room temperature produces stable oil-in-water (o/w) Pickering emulsions in the absence of Ostwald ripening. The oil droplets are decorated by stacks of crystalline discs. The stacking of these discs is controlled by charge regulation as derived from conductivity, scattering and zeta potential measurements. Catanionic nanodiscs are ideal solid particles to stabilize Pickering emulsions since they present no density difference and a structural surface charge which is controlled by the molar ratio between anionic and cationic components. The contact angle of catanionic nanodiscs at a water/oil interface is also controlled by the non-stoichiometry of the components. The resulting energy of adhesion and the repulsion between droplets is much larger than kT. As a consequence of these unique properties of nanodiscs, this type of emulsions presents an extremely high resistance towards coalescence and creaming, even in the presence of salt.