Understanding the Effect of the Oil-to-Surfactant Ratio on Eugenol Oil-in-Water Nanoemulsions Using Experimental and Molecular Dynamics Investigations

Nanoemulsions (O/W) are finding their way to achieve a higher encapsulation of bioactive molecules for a better shelf life. In the present study, the effect of the oil to surfactant ratio on the eugenol-water emulsion stabilized with Tween 80/Span 80 is investigated experimentally and theoretically using molecular dynamics simulation (MDS). In the experiment, the emulsions were prepared at oil to surfactant ratios of 1:1, 2:1, and 3:1. The droplet size obtained at various ratios was found to be in the range of 164-210 nm with uniform distribution and was monodisperse in nature. Optical microscopic analysis clearly showed that the droplets formed were spherical and possessed good stability against phase aggregation. Besides that, the MDS of the system was performed to study the interaction between eugenol and emulsifiers, the behavior of surfactants at the interface, and the dynamic change in the droplet size. The MDS confirmed the formation of a cluster of eugenol and surfactants in the spherical droplet form at various oil-surfactant ratios. To probe the stabilization of the eugenol droplet, the properties such as diffusion coefficient, radius of gyration, end-to-end distance, and radii were evaluated and critically compared at all of the considered ratios. The obtained results highlighted the importance of the oil-surfactant composition and provided atomistic insights into the formation of a stable eugenol emulsion. Based on the findings, the prepared concentrated emulsions were stable and could be used to achieve a higher loading capacity of hydrophobic molecules.