Behaviour of hybrid inside/out Janus nanotubes at an oil/water interface. A route to self-assembled nanofluidics?

Imogolites are natural aluminosilicate nanotubes that have a diameter of a few nanometers and can be several microns long. These nanotubes have different chemical groups on their internal (Si-OH) and external (Al-OH-Al) surfaces, that can be easily functionalised independently on both surfaces. Here we show that taking advantage of the particular shape and chemistry of imogolite, it is possible to prepare inside/out Janus nanotubes. Two kinds of symmetric Janus nanotubes are prepared: one with an external hydrophilic surface and an internal hydrophobic cavity (imo-CH3 ) and one with an external hydrophobic surface and a hydrophilic internal cavity (OPA-imo). The behaviour of such inside/out Janus nanotubes at oil/water interfaces is studied. The OPA-imo adsorbs strongly at the oil/water interface and is very efficient in stabilising water-in-oil emulsions through an arrested coalescence mechanism. Imo-CH3 also adsorbs at the oil/water interface. It stabilises oil-in-water emulsions by inducing slow oil-triggered modifications of the viscosity of the continuous phase. The possible transport of small molecules inside the imo-CH3 nanotubes is evidenced, opening up routes towards self-assembled nanofluidics.