Early Detection of Lamellar Gel Network Instability in Cosmetic Emulsions Using Rheology, Laser Diffraction, and AI-Assisted Microscopy

Standard ISO testing of cosmetic emulsions offers limited insight into the microstructural mechanisms governing long-term stability. We hypothesize that a single weight-percent increase in emulsifier concentration is sufficient to determine, through its effect on inter-bilayer junction connectivity, whether the lamellar gel network consolidates or fails. To test this, we apply a two-tier strategy combining ISO/TR 18811 testing and Turbiscan turbidimetry with rheology, laser diffraction, and AI-assisted polarized light microscopy, on two oil-in-water emulsions structured by a lamellar gel network and stabilized by Cetearyl Alcohol/Cetearyl Glucoside at 2 wt% (Emulsion A) and 3 wt% (Emulsion B) over 30 days of storage. First-tier testing distinguished formulations only at Day 30; Turbiscan index values (2.64, 1.78) stayed below threshold throughout. The second-tier protocol resolved structural divergence from Day 8 to 15, two to three weeks earlier. In Emulsion A, a transient birefringent fraction (51.5% at Day 8) preceded network disruption, droplet coalescence, and a drift of the loss tangent toward more liquid-like values. In Emulsion B, birefringence expanded to 98.4% by Day 30 and the loss tangent declined to 0.325. These results indicate that a 1 wt% difference in emulsifier concentration, within a range of industrial use, is sufficient to determine whether the lamellar gel network consolidates or fails, and that combining rheology, laser diffraction and AI-assisted microscopy resolves this divergence two to three weeks before conventional ISO criteria are met.