Salt-induced edible anisotropic Pickering emulsion droplets

Pickering emulsions, with anisotropic droplets, are often prepared via methods that involve long procedures or require elevated temperatures, exotic particles and equipment, thereby limiting their industrial applications. Herein, we report a facile method for preparing anisotropic Pickering emulsion droplets which does not require elevated temperatures, exotic particles and equipment. This method involves measuring 7 cm³ of different concentrations of aqueous NaCl solution (0 to 1000 mM) into separate screw cap glass vials, adding 4 wt.% rod- or cube-shaped CaCO₃ particles, followed by 7 cm³ of vegetable oil. The salt solution-particle-oil mixtures are then sheared at 13000 rpm for 3 min. It was found that mixtures containing the cube-shaped CaCO₃ particles formed oil-in-water emulsions with anisotropic droplets (length ≤ 2430 μm) while those containing the rod-shaped ones formed emulsions with isotropic droplets (diameter ≤ 800 μm). The results also revealed that the aspect ratio of the anisotropic droplets is between 2.7 to 3.3, depending on NaCl concentration. In addition, the fraction of aqueous and oil phases resolved for three years is within 0.2 to 0.6 and ≪ 0.1, respectively, depending on NaCl concentration. Zeta potential measurement shows a decrease in the magnitude of particle charge with increasing salt concentration: a strong decrease for mixtures with cube-shaped CaCO₃ particles and a weak decrease for mixtures with the rod-shaped ones.