Abstract
Water-in-oil-in-water (W/O/W) multiple emulsions are thermodynamically unstable systems characterized by high interfacial free energy and complex thermodynamic driving force promoting internal droplet coalescence or Laplace pressure-driven water migration. In color cosmetics such as liquid foundations, this intrinsic instability is further exacerbated by the incorporation of inorganic pigments (e.g., titanium dioxide (TiO(2)) and iron oxides), which perturb the delicate interfacial equilibrium and trigger premature phase separation. Utilizing polyglyceryl-10 stearate (PG10S) as a fixed oil-in-water (O/W) emulsifier, this study systematically investigated the stability of these challenging systems by assessing four polyglycerol-based water-in-oil (W/O) emulsifiers with distinct molecular architectures: polyglyceryl-3 polydimethylsiloxyethyl dimethicone (KF-6106), polyglyceryl-6 polyricinoleate (PR-15), polyglyceryl-3 polyricinoleate (PG3PR), and polyglyceryl-2 dipolyhydroxystearate (PGPH). Through a combination of confocal laser scanning microscopy (CLSM), rheometry, differential scanning calorimetry (DSC), surface/interfacial tension analysis, and accelerated stability testing, the structure-property relationships governing the integrity of the multiple-layered structure under both intrinsic and pigment-induced stresses were elucidated. The results demonstrate that the silicone-modified emulsifier (KF-6106) exhibited superior stabilizing efficacy, achieving a high thixotropic recovery of 91.16%. This performance is attributed to its ability to form a resilient, "self-healing" interfacial film with high segmental mobility, which effectively suppresses the spontaneous merging of internal droplets and maintains a robust barrier against the destabilizing effects of pigment particles. These findings establish a mechanistic framework for optimizing emulsifier selection and provide theoretical guidance for the rational design of stable, high-performance W/O/W multiple emulsions in complex, particle-filled systems.