Pyrrolidinium ionic liquid and Polysorbate 20 based nanoemulsions of lambda-cyhalothrin: formulation, physicochemical...

Hydrophobic pesticides often exhibit poor aqueous dispersibility and limited wettability, which can adversely affect their application efficiency. To address these limitations, ionic liquid (IL)-based nanoemulsions (NEs) incorporating the hydrophobic insecticide lambda-cyhalothrin (LCT) were developed using Polysorbate 20 and two pyrrolidinium ILs, 1-octyl-1-methylpyrrolidinium bromide ( $\mathrm{Pyr}{C}_8{\mathrm{Br}}^{-}$ ) and 1-dodecyl-1-methylpyrrolidinium bromide ( $\mathrm{Pyr}{C}_{12}{\mathrm{Br}}^{-}$ ), in an aqueous medium.

Stable LCT-loaded NEs with nanosized droplets were successfully prepared via ultrasonication. The concentration for the ILs required for the NE formation was found to be 2.39 mm for $\mathrm{Pyr}{C}_8{\mathrm{Br}}^{-}$ and 0.70 mm for $\mathrm{Pyr}{C}_{12}{\mathrm{Br}}^{-}$ . Scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging confirmed the formation of the NEs, revealing uniformly dispersed, nanosized droplets without noticeable coalescence following pesticide loading. The alkyl chain length of the IL strongly influenced the physicochemical properties of the formulations, with the $\mathrm{Pyr}{C}_{12}{\mathrm{Br}}^{-}$ based NE showing greater LCT incorporation than the $\mathrm{Pyr}{C}_8{\mathrm{Br}}^{-}$ system. Spectroscopic analysis further supported the interaction between the IL, LCT, and the surfactant within the NE matrix. Contact angle measurements on chili and lemon leaves showed markedly lower values for LCT-loaded NEs compared to LCT alone, indicating improved surface wetting. Density functional theory (DFT) calculations corroborated these findings, predicting stronger intermolecular interactions and greater stability for the $\mathrm{Pyr}{C}_{12}{\mathrm{Br}}^{-}$ -LCT system.

The developed pyrrolidinium IL-based NEs provide a stable and effective formulation for incorporating LCT while improving its wetting behavior. The experimental findings, supported by theoretical calculations, demonstrate that IL alkyl chain length plays a key role in governing NE stability and pesticide incorporation, highlighting the potential of these systems as carriers for hydrophobic pesticides. © 2026 Society of Chemical Industry.