Salt-induced edible anisotropic Pickering emulsion droplets

Abstract

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.

GRAPHICAL ABSTRACT

Keywords:

• Pickering emulsions
• non-spherical droplets
• particle jamming
• microcapsules
• microencapsulation

Acknowledgements

The Tertiary Education Trust Fund (TetFund) of Nigeria is thanked for sponsorship and Maruo Calcium Company, Japan, is thanked for supplying the calcium carbonate particles. We also thank the editor and the two anonymous reviewers for the useful comments which have helped us improve the paper.

Disclosure statement

The authors declare that they have no conflict of interest.

Author contributions

Conceptualization, Investigation, Methodology, Resources, Visualization, Validation, Writing-Original Draft: A.T.T; Writing-Review and Editing: M.T. and E.E.U.

Additional information

Funding

This work was funded by the Tertiary Education Trust Fund (TetFund) of Nigeria.