Pickering emulsions stabilized by inside/out Janus nanotubes: Oil triggers an evolving solid interfacial layer

[Display omitted] In the field of Pickering emulsion, original inside/ouside Janus clays nanoparticles are investigated for their emulsification properties. Imogolite is a tubular nanomineral of the clay family having both inner and outer hydrophilic surfaces. A Janus version of this nanomineral with an inner surface fully covered by methyl groups can be obtained directly by synthesis (Imo-CH3, hybrid imogolite). The hydrophilic/hydrophobic duality of the Janus Imo-CH3 allows the nanotubes to be dispersed in an aqueous suspension and enables emulsification of non-polar compounds due to the hydrophobic inner cavity of the nanotube. Through the combination of Small Angle X-ray Scattering (SAXS), interfacial observations and rheology, the stabilization mechanism of imo-CH3 in oil-water emulsions has been investigated. Here, we show that interfacial stabilization of an oil-in-water emulsion is rapidly obtained at a critical Imo-CH3 concentration as low as 0.6 wt%. Below this concentration threshold, no arrested coalescence is observed, and excess oil is expelled from the emulsion through a cascading coalescence mechanism. The stability of the emulsion above the concentration threshold is reinforced by an evolving interfacial solid layer resulting from the aggregation of Imo-CH3 nanotubes that is triggered by the penetration of confined oil front into the continuous phase.