Interfacial behavior of neem oil (Azadirachta indica): Experimental and computational insights

Neem oil (NO) is a natural, bioactive extract derived primarily from neem seeds. Renowned for its antimicrobial, antifungal, antioxidant, pesticide, and insecticidal properties, NO is a highly effective and eco-friendly alternative to synthetic chemicals in agricultural, food, and medical applications. The interfacial properties of NO were assessed by measuring its effect as an additive on the formulation of microemulsions (MEs) and nano- emulsions (NEs). Formulation scans were employed to evaluate the effect of NO on surfactant-oil-water (SOW) systems under optimum formulation conditions. The results indicate that adding NO to the oil phase shifts the hydrophilic-lipophilic balance (HLB) value, at optimum formulation, from 9.5 to 11.5, suggesting that the additive contributes to the emulsification of the oil phase. Maltese cross patterns were observed on polarized light micrographs taken from the ME containing NO, indicating the presence of lamellar liquid crystals (LCs). NEs generated by a low-energy emulsification method displayed droplet size significantly lower droplet sizes (11-22 +/- 1) nm than those obtained by high-energy methods. Molecular dynamics (MD) simulations revealed the hydrophilic nature of azadirachtin, the key bioactive component of NO, at the water/n-decane interface, providing molecular evidence of its interfacial behavior. These findings pave the way for future research to enhance NO's interfacial properties, potentially leading to more eco-friendly products and applications.