High-internal phase emulsions stabilized by colloidal Zr-based solid clusters

Emulsions stabilization via in situ colloidal sol-gel process based on a quaternary system [zirconyl nitrate + acetylacetone + ammonia + water] has been investigated. By adding dodecane into this quaternary system, we showed how nanoparticle Zr-based clusters were adequate surface active to stabilize oil in water emulsions. In most cases, these clusters are so effective that stabilization of oil-in-water high-internal phase emulsions (HIPE) containing a majority of dodecane is achieved. We have studied the effects of Zr-precursor concentration, complexing agent amount (acetylacetone) and pH on the nanoparticles activity at dodecane/water interface. In particular, acetylacetone acted like a steric barrier promoting the nanoparticle dispersion. This barrier led to the formation of more Zr-based nanoparticles exhibiting a more efficient stabilization of the emulsion. It is noteworthy that no significant evolution of the emulsion morphology was observed by decreasing the Zr-precursor concentration. Basically, the drop size polydispersity was still high contrary to the case of the well-known limited coalescence phenomenon that generally occurs for Pickering emulsions dilution. Here, the effectiveness of these nanoparticle Zr-based clusters to prevent coalescence was mainly due to droplets gelation thanks to inter-nanoparticle irreversible bridging effect. These emulsions are devoted to be used as precursor for porous zirconia synthesis with oil droplets as soft template to promote macroporosity. Therefore, the understanding of the behavior of these emulsions is crucial to precisely control the morphology of these specific materials. (C) 2014 Elsevier B.V. All rights reserved.