A facile route for the preparation of water-in-oil-in-water (w/o/w) double emulsions is described for three model oils, namely n-dodecane, isopropyl myristate and isononyl isononanoate, using fumed silica particles coated with poly(ethylene imine) (PEI). The surface wettability of such hybrid PEI/silica particles can be systematically adjusted by (i) increasing the adsorbed amount of PEI and (ii) addition of 1-undecanal to the oil phase prior to homogenization. In the absence of this long-chain aldehyde, PEI/silica hybrid particles (1.0 wt % fumed silica, PEI/silica mass ratio = 0.50) produce o/w Pickering emulsions in all cases. On addition of sufficient 1-undecanal, this reagent reacts with the primary amine groups on the PEI chains, which renders the PEI/silica hybrid particles sufficiently hydrophobic to stabilize w/o Pickering emulsions at 20oC. 1H NMR, gas chromatography and x-ray photoelectron spectroscopy provide compelling experimental evidence for this in situ Schiff base surface chemistry, while a significant increase in water contact angle indicates markedly greater surface hydrophobic character for the PEI/silica hybrid particles. However, when PEI/silica hybrid particles are prepared using a relatively low adsorbed amount of PEI (1.0 % w/w fumed silica, PEI/silica mass ratio = 0.075), the extent of surface modification achieved using this Schiff base chemistry is insufficient, and only o/w Pickering emulsions can be obtained. Fluorescence microscopy and laser diffraction studies confirm that highly stable w/o/w double emulsions can be achieved for all three model oils. Dye release studies from the internal aqueous cores into the aqueous continuous phase indicate some immediate loss of dye (12-18 %) during the high speed homogenization required for double emulsion formation, but no further dye release is observed at 20 �C for at least 15 days thereafter.

Preparation of double emulsions using hybrid polymer/silica particles: New Pickering emulsifiers with adjustable surface wettability

248th National Meeting (2014)

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