Porous Ceramics via Processable Pickering Emulsion Stabilized by Oppositely Charged Colloids

Abstract

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.

Macroporous Ceramic Monolith from Nanoparticle–Polyelectrolyte-Stabilized Pickering Emulsions

“…Controlled drying of the oil-in-water emulsion gels, which upon evaporation of both water and oil results in a ceramic green body, constitutes an important step in the fabrication of porous ceramic. , The conditions used for drying must be such that the pore former, i.e., which in this case predominantly is oil, evaporates without any damage to the shape and structural integrity of the final ceramic green body. The gelled emulsions were dried under a controlled environment in a humidity chamber maintained at 35 °C and 55% RH.…”

“…The emulsion stabilized by heteroaggregates of oppositely charged particle−polyelectrolyte mixture was dried in a humidity chamber under controlled conditions (at 35 °C and 55% RH) to obtain a green emulsion body. 32 Thermogravimetric analysis (TGA) was performed for the ceramic green body using a thermogravimetric analyzer (TA Instruments). The sample was subjected to a temperature ramp at 10 °C/min under air atmosphere.…”

“…Although these emulsions with controlled drop size distribution are expected to serve as excellent templates for the fabrication of porous materials, the low particle concentration used in these studies poses problems during their processability. Moreover, the colloidal processing route for the fabrication of porous materials, especially emulsion templating routes, requires high particle loading. , In the present study, particle–polyelectrolyte complex-stabilized emulsions are used as templates for the production of a porous ceramic monolith. To this end, gel-like Pickering emulsions that can be easily processed are prepared and converted into porous ceramic by drying and sintering.…”

“…Moreover, the colloidal processing route for the fabrication of porous materials, especially emulsion templating routes, requires high particle loading. 32,33 In the present study, particle−polyelectrolyte complex-stabilized emulsions are used as templates for the production of a porous ceramic monolith. To this end, gellike Pickering emulsions that can be easily processed are prepared and converted into porous ceramic by drying and sintering.…”

Pickering Emulsions Simultaneously Stabilized by Starch Nanocrystals and Zein Nanoparticles: Fabrication, Characterization, and Application

“…Alternatively, using two types of particles has been shown to synergistically stabilize Pickering emulsions, especially when the use of either type of particle alone does not stabilize the emulsion. , Different stabilization mechanisms have been proposed to account for the emulsion stabilized by dual particles. − Binks et al, for example, described how hetero-aggregations formed through the electrostatic attraction of silica particles with opposite charges before emulsification has suitable wettability for stabilizing the Pickering emulsion . Similarly, Nallamilli et al found that hetero-aggregations of oppositely charged polystyrene (PS) particles assemble easily at the o/w interface and further rearrange for forming a monolayer of closely packed particles at the interface .…”