Tuning Micellar Hydrophobicity for Enhanced Deposition, Spreading, and Solubilization of Hydrophobic Pesticides on Plant Wax Surfaces

Surfactants are essential components of pesticide adjuvants, facilitating the solubilization of active ingredients, promoting droplet deposition on hydrophobic or superhydrophobic leaf surfaces, and enhancing uptake by plant tissues. However, the effect of deposited surfactant droplets on the interactions with plant waxes remains poorly understood. In this study, spherical micelles with tunable hydrophobicity were prepared by assembling fatty acids of varying alkyl chain lengths─decanoic (C10), lauric (C12), myristic (C14), and palmitic (C16) acids─with the branched organic base tetrabutylammonium hydroxide. Aqueous droplets containing more hydrophobic micelles exhibit slower retraction upon a high-speed impact on hydrophobic wax films, maintain larger contact areas during evaporation, and demonstrate a stronger solubilization of hydrophobic pesticides. Increasing the chain length of the fatty acid enhances both micellar self-assembly and surface activity in solution. To mimic plant leaf wax, 1-octacosanol films with a water contact angle of ∼120° were employed. Micelles with higher hydrophobicity display increased surface activity, faster molecular diffusion, and stronger interactions with wax molecules, resulting in larger retention areas after deposition and evaporation. These interactions also improve the fluidity of the wax layer, potentially facilitating pesticide penetration into the leaves. This work highlights the critical role of micelle–wax interactions in determining surfactant performance as pesticide adjuvants and provides insights into optimizing droplet behavior and pesticide efficacy.