The influences of Na⁺, Ca²⁺ on the water-in-oil Pickering emulsion stabilized by stearic acid modified hydrophobic calcium carbonate particles

The properties of Pickering emulsions is affected by many factors, one of the most typical of which is the ionic environment. Existing studies have mainly focused on the effect of ions in the continuous phase on oil-in-water Pickering emulsions, and usually only single species of ions are studied. The water-in-oil Pickering emulsions are commonly used to encapsulate a variety of water-soluble functional substances, which often contain various of ions. Therefore, it is necessary to study the effect of ions in the internal phase on the properties of inverse Pickering emulsions. The inverse Pickering emulsions with an average droplet size of 100 mu m were prepared using hydrophobized calcium carbonate particles. Subsequently, Na+ and Ca2+ were introduced into the internal phase to investigate their effects on the emulsion. The results show that the presence of Na+ can aggravate droplet coalescence, and Ca2+ can cause severe damage to the emulsions and even lead to phase inversion. It was speculated that Na+ can weaken the surface charge of particles by compressing the electric double layer, resulting in lower electrostatic repulsion between particles, thus changing the dispersion state of the particles and ultimately affecting the properties of the emulsion. And Ca2+ can combine with and release stearate from the particle surface through chemical reactions, thus changing the wettability of the particles and resulting in breaking and phase inversion of the emulsions. The present work is informative for the setting of the phase composition and the prediction of stability during the application of inverse Pickering emulsions.