Stability of electrostatically stabilized Pickering emulsion of silica particles and soy hull polysaccharides: Mechanism of pH and ionic strength

To enhance the surface hydrophobicity and emulsification capacity of silica colloidal particles, a natural surface modification of soy hull polysaccharides (SHP) was conducted. Here, the effects of pH and ionic strength on the stability, microstructure and rheological properties of concentrated Pickering emulsions were investigated. Experimental results show emulsions gelled at pH 2, with increasing pH (2-10), SiO₂-SHP absolute zeta potential (from -19.6 to -44.7 mV) and interfacial tension (from 15.2 to 25.09 mN/m) increased, and viscosity, viscoelasticity and storage stability decreased. Additionally, at low NaCl concentrations (<150 mM), SiO₂-SHP interfacial tension remained low (21.3 mN/m), promoting stable emulsions (TSI < 1.5). In this case, the electrostatic interaction was slightly affected by ions, facilitating the occurrence of composite coagulation. However, as ionic concentration increased (150-300 mM), interfacial tension increased (from 20.5 to 27.6 mN/m). Thus, our study presents important insights into the pH and salt ions dependent mechanism of emulsion stabilization by SiO₂-SHP.