Intermolecular network reorganization induced by hydroxyethyl cellulose enables structurally stable niacinamide-based soft matter systems.

In this study, a structurally stable skin-brightening moisturizing cream was developed through the incorporation of hydroxyethyl cellulose (HEC) as a functional polymer additive. Niacinamide was employed as the active ingredient, and the physicochemical properties and performance of the formulations were systematically evaluated using bioelectrical impedance analysis (BIA), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The incorporation of HEC significantly enhanced skin hydration performance and produced a moderate improvement in thermal stability compared with the HEC-free formulation. FT-IR analysis revealed a redistribution of intermolecular interactions, most notably in the ether (C-O-C), and OH stretching regions, indicating the formation of a reorganized polymer network within the cream matrix. Whereas the carbonyl (C=O) region showed only a minor and localized change. SEM observations confirmed improved morphological integrity under both thermal and sunlight-exposure conditions, while TGA demonstrated a slight increase in decomposition temperature, suggesting enhanced thermal resistance. HEC forms a physically entangled polymer network that establishes secondary intermolecular interactions with surrounding components, including fatty alcohols, glycerin, and niacinamide. This network enhances structural coherence, stabilizes the oil-water interface, and suppresses moisture loss.