Effects of the zeolite concentration on the microstructure of high internal phase emulsions stabilized by surfactant-coated zeolite particles

The shaping of powdery zeolites into hierarchical materials is an objective for numerous applications. Emulsions can be used as a soft template to create porous and monolithic materials, but a fine understanding and control of the microstructure of the emulsions is crucial. By relating rheological, microscopic observations and microstructural properties, this study highlights the influence of the zeolite content (1-8 wt%) on the microstructure of high internal phase emulsions (HIPEs) stabilized by tetradecyltrimethylammonium bromide (TTAB)-covered zeolite particles. Pickering oil-in-water (O/W) emulsions are obtained at low surfactant/zeolite weight ratios (< 0.2 wt/wt), while surfactant-stabilized emulsions form at high surfactant/zeolite weight ratios (2-7 wt/wt). The properties of the surfactant stabilized emulsions depend little on the concentration of zeolite particles. The droplets are only a few microns in diameter and because the bilayer surfactant-coated zeolite particles repulse each other, the emulsions have a creamy aspect and flow smoothly. In the Pickering emulsions however, droplet size and network strength depend strongly on the concentration of zeolite particles, which agglomerate when in excess and create a secondary network of agglomerated flocs in the continuous phase. At sufficient zeolite concentrations the unusual flow behavior of the emulsions suggests that the secondary network interconnects with the particles adsorbed at the oil-water interface.