Rheological Insights: The Role of Divalent Ions on the Stability and Phase Behavior of Oil–Water Emulsions

Furthermore, we identified phase inversion in CaCl₂ systems and evidence of multiple emulsions (O/W/O) in MgCl₂ systems, both at 8000 ppm and 5.0% v/v surfactant. To complement the experimental analysis, we developed a custom Python-based tool, ROJA, for automated image analysis and statistical characterization of emulsion droplets. We suggest that intermolecular forces and increased friction due to electrostatic interactions between Ca²⁺ and the anionic surfactant led to higher viscosities and smaller, more concentrated droplets (as low as 54.27 μm at 25,000 ppm) at higher salinities.

In contrast, Mg²⁺ emulsions showed lower viscosities due to larger droplets (up to 127.87 μm at 25,000 ppm), resulting in fewer droplet–droplet interactions. The presence and concentration of divalent ions are therefore critical for the performance of O/W emulsions in petroleum industry applications.