Effect of emulsifying process on stability of pesticide nanoemulsions

Abstract

Abstract The effect of addition sequence of organic/aqueous phases and initial location of emulsifiers on the stability of pesticide nanoemulsions was systematically investigated by monitoring the appearance of nanoemulsions and analyzing the optical micrograph of droplets, variation in droplet size, Turbiscan Lab scanning spectrum, and crystallization temperature. Pesticide nanoemulsions prepared with similar formulation (beta-cypermethrin as oil-soluble technical pesticide, methyl oleate as organic solvent, polyoxyethylene castor oil ether as emulsifiers, and deionized water) but through different emulsifying processes showed evidently different levels of stability. Nanoemulsion A, which was prepared by adding aqueous phase into organic phase with emulsifiers, displayed the highest stability, uniform appearance, smallest and scattered droplets that do not change with time, lowest crystallization temperature, and a slight change in delta backscattering. The stability of nanoemulsion C (prepared by adding organic phase with emulsifiers into the aqueous phase) comes second. By contrast, nanoemulsions B (prepared by adding organic phase into the aqueous phase with emulsifiers) and D (prepared by adding aqueous phase with emulsifiers into the organic phase), exhibited creaming, larger and serried droplets that increased with time, higher crystallization temperature, an obvious change in delta backscattering, and worse stability.