pH-Sensitive W/O Pickering High Internal Phase Emulsions and W/O/W High Internal Water-Phase Double Emulsions with Tailored Microstructures Costabilized by Lecithin and Silica Inorganic Particles

Synergistic stabilization of Pickering emulsions by a mixture of surfactants and colloidal particles has received increasing interest in recent years but only a few of them can produce high internal phase double emulsions (HIPDEs) with good stability. In this study, we present a feasible and common method of preparing Pickering high internal phase emulsions (HIPEs) with tunable inner morphology costabilized by a biosurfactant lecithin and silica nanoparticles. We investigate the influence of the pH value on the interfacial behavior of lecithin and elucidate the synergistic mechanism between lecithin and silica nanoparticles in different conditions in the stability of as-prepared emulsions. Specifically, water-in-oil (W/O) Pickering HIPEs can be successfully stabilized by lecithin and hydrophobic silica nanoparticles in a wide pH range (pH 1-10), while catastrophic phase inversion occurred at high pH values (pH ≥ 11). Interestingly, stable water-in-oil-in-water (W/O/W) high internal phase double emulsions (HIPDEs) can also be prepared via a two-step method by the cooperation of lecithin and silica nanoparticles. Moreover, functional interconnected porous monoliths and microspheres are facilely fabricated by emulsion templates and their potential applications are explored.