Dispersion kinetics and release behavior of eugenol from ternary water/eugenol/Poloxamer 407 systems: Toward ecofriendly larvicide formulations

Abstract

Essential oil–based insecticides are limited by poor water solubility and uncontrolled dispersion in aquatic environments. This study investigates ecofriendly delivery systems based on ternary water/eugenol/Poloxamer 407 (P407) formulations for potential application in Aedes aegypti breeding sites. Emulsions, gel-like emulsions, and gels were prepared and diluted in water to a final eugenol concentration of 90 ppm. Dispersion kinetics, spatial distribution, mechanical energy requirements, and larvicidal efficacy were evaluated by UV–Vis measurements, fluorescence spectroscopy, and controlled agitation experiments. Fluorescence analysis demonstrated that dilution reduced the P407 concentration below its critical micelle concentration, inducing micellar disassembly and release of eugenol into the aqueous phase. Under quiescent conditions, emulsions exhibited faster but spatially heterogeneous dispersion, reaching ∼40–60 % of the nominal concentration after 120 min, whereas gels displayed slower, diffusion-controlled release with uniform but limited dispersion (<15 %). Mild mechanical agitation (15–45 s) eliminated concentration gradients and enabled complete eugenol homogenization across all formulations. Larvicidal bioassays against Aedes aegypti revealed comparable efficacy among formulations, with LC₅₀ values ranging from 71 to 99 ppm, indicating that biological activity depends primarily on the final bioavailable eugenol concentration rather than on formulation architecture. These results demonstrate that polymer-based formulation structure governs dispersion and release kinetics without compromising larvicidal effectiveness, offering a versatile platform for sustainable vector control applications.