Abstract
Emulsions consist of two (or more) immiscible liquids wherein one of the liquids is dispersed in the other as droplets. Similar to surfactants, solid particles can also act as efficient emulsifiers and the emulsion so formed are popularly known as Pickering emulsions.The formation, microstructure, as well as processability of such emulsions can be tuned by controlling the physico-chemical properties of the particles. There is a growing interest in the development of processable Pickering emulsions and the current research mainly focus on the design of emulsion stabilisers, methods of emulsion fabrication, methods to tune the rheological properties of emulsion, and the development of functional materials derived from them.
In the present work, we propose a simple and modular approach to realize processable Pickering emulsions from mixtures of commercially available oppositely charged fumed oxide particles and a combination of fumed oxide particles and polyelectrolyte. The ability of weakly charged hetero-aggregates to adsorb at the oil-water interface favors the formation of highly stable emulsions. Control over the microstructure, rheology and processability of the Pickering emulsion is modulated by tuning emulsion formulation parameters. The processability of Pickering emulsion is demonstrated by 3D printing using a direct ink writer and theoptimum conditions for producing a printable emulsion ink are identified. Further, porous ceramics have been fabricated from the emulsion template by drying and sintering. Effects of various parameters such as the sintering procedure and the emulsion formulation parameters on the phase evolution, microstructure, and pore characteristics have been studied. Thereafter, a novel semi-batch and continuous process for formulating highly stable Pickering emulsions by condensing steam on subcooled oil containing hydrophobic nanoparticles is developed. The effect of process and formulation parameters on the mean diameter and the size distribution of the droplets are investigated. The process proposed allows the preparation of emulsions in a rapid, reproducible, scalable, and energy-efficient manner and can be used as an efficient template for the fabrication of functional materials. Finally, emulsion formulations are used for preparing functional materials for catalyst supports, thermal insulation, oil water separation, and encapsulation.
Keywords:Pickering Emulsion, hetero-aggregation, Rheology, 3D printing, Porous ceramics, Steam condensation