We report a method to produce processable Pickering emulsions in which electrostatic heteroaggregation of oppositely charged fumed silica and alumina particles is exploited. The ability of weakly charged heteroaggregates to adsorb to the oil–water interface favors the formation of highly stable emulsions. A control over the microstructure and rheology of the Pickering emulsion is demonstrated by tuning parameters such as composition, pH, and total concentration of particles. The Pickering emulsions formed under optimal conditions are found to be gel-like and are excellent templates for the fabrication of porous ceramics. Furthermore, the porous mullite ceramic structure which has exceptional thermal and chemical resistance under harsh environments is obtained by drying and sintering of the emulsion template. The phase evolution, microstructure, and porosity of the resulting ceramic are characterized.

In this work, we present a simple and scalable approach for fabricating porous ceramic from emulsions stabilized by a binary mixture of oppositely charged nanoparticles and a polyelectrolyte. The electrostatic heteroaggregation is exploited to form weakly charged particle−polyelectrolyte complexes (PPCs) that readily stabilize oil-in-water emulsions. The concentration of surface-active PPCs is varied to obtain Pickering emulsion gels that can be processed and converted into the macroporous ceramic structure. The polyelectrolyte in the binary mixture not only enables the adsorption of particles to the oil−water interface and renders processability of the emulsions but also acts as a binder. Nearly one-to-one correspondence between the microstructure of the green ceramic obtained after the evaporation of solvents from the gel-like emulsions and the parent emulsions is observed. The green ceramic is further sintered under controlled conditions to obtain a porous ceramic monolith. We demonstrate that the microstructure and the pore size distribution in the final ceramic can be altered by tuning the composition of the individual species used in the emulsion formulation, i.e., by optimization of the particle−polyelectrolyte ratio used in the processing route.

The aggregation of oppositely charged soft materials (particles, surfactants, polyelectrolytes, etc.) that differ in one or more physical or chemical attributes, broadly referred to as electrostatic heteroaggregation, has been an active area of research for several decades now. While electrostatic heteroaggregation (EHA) is relevant to diverse fields such as environmental engineering, food technology, and pharmaceutical formulations, more recently there has been a resurgence to explore various aspects of this phenomenon in the context of interface stabilization and the development of functional materials. In this Feature Article, we provide an overview of the recent contributions of our group to this exciting field with particular emphasis on fundamental studies of electrostatic heteroaggregation between oppositely charged systems in the bulk, at interfaces, and across the bulk/interface. The influence of the size and shape of particles and the surface charge of heteroaggregates on the formation of Pickering emulsions and their utilization in the development of porous ceramics is discussed.

We propose a versatile strategy for the production of highly stable water in oil Pickering emulsion by direct contact condensation of steam. In contrast to conventional methods that use of...

No abstract