Exploring the link between interfacial and bulk viscoelasticity in reverse Pickering emulsions

Abstract

The relationship between interfacial and bulk emulsion viscoelasticity is investigated. Water-in-dodecane reverse Pickering emulsions, with a dispersed phase volume fraction of 0.66, stabilized with partially hydrophobic silica particles are addressed. Interfacial and bulk viscoelastic properties are probed via 2D and 3D oscillatory shear rheology. The silica particles concentration and NaCl content have been varied. In the whole range of concentrations studied the elastic modulus (G′) remains always greater than the viscous modulus for 2D and 3D rheology. The viscoelastic behavior can be related to the silica concentration both at the interface and in the emulsion. Power law dependences towards the silica content are recorded for the interfacial and the bulk emulsion elastic modulus. When increasing the NaCl concentration, the viscoelastic properties both at the interface and in the emulsion become stronger. The amount of silica and NaCl produces similar effects on both the interface and bulk viscoelastic properties. The increase of their concentration induces a rigidification of the dodecane/water interface since GP′(interface) increases. Such interfacial hardening produces a rigidification of the droplets (GP′(Emulsion) is enhanced). Correlations between the interfacial and bulk emulsion viscoelasticity are also extracted from the experimental data. This is the first time that these kinds of relationship are reported. These results highlight that everything that affects the interfacial viscoelasticity is reflected on the bulk scale of emulsions.