Not Just Water: Ionic Influence on the Rheology of Natural O/W Emulsions

Abstract

BACKGROUND: The study investigates how different aqueous phases—purified water, two mineral waters, and one thermal mineral water—affect the physicochemical and mechanical properties of oil-in-water emulsions stabilized with two non-ionic alkyl polyglucoside (APG) emulsifiers—Montanov™68 (Cetearyl Alcohol and Cetearyl Glucoside) and Montanov™82 (Cetearyl Alcohol and Coco Glucoside). Comprehensive characterization included pH and conductivity measurements, microscopy, rheology, and texture analysis. Given the routine adjustment of topical emulsions to skin-relevant pH, rheological measurements were repeated after adjusting each formulation to pH 5.5. RESULTS: Unlike electrolyte effects typically described for ionic surfactant systems, this work demonstrates that ion identity and mineralization level of the aqueous phase significantly influence structure and mechanical properties of emulsions stabilized by non-ionic APG emulsifiers, which are generally assumed to be insensitive to electrolytes. Distinct mineral compositions produced measurable changes in viscosity, firmness, and viscoelastic behaviour, revealing that mineral waters actively modulate lamellar gel network organization. In contrast, adjusting the pH to 5.5 resulted in minor changes, confirming that aqueous ionic composition is the dominant factor shaping the final emulsion properties. CONCLUSION: These findings provide the first evidence that, in APG-stabilized emulsions, the water phase functions as an active structural component rather than an inert solvent. Different performances of structurally similar emulsifiers towards the same electrolytes profile indicate how small variations in lamellar architecture can lead to different outcomes. Consequently, the choice of mineral or thermal water can be strategically used as a formulation tool to deliberately tailor the texture, rheology, and structural organization of natural emulsions. © 2025 Society of Chemical Industry (SCI)