Cationic\nAmphiphilic Comb-Shaped Polymer Emulsifier\nfor Fabricating Avermectin Nanoemulsion with Exceptional Leaf Behaviors\nand Multidimensional Controlled Release

The\ndevelopment of intelligent multifunctional nanopesticides featuring\nenhanced foliage affinity and hierarchical target release is increasingly\npivotal in modern agriculture. In this study, a novel cationic amphiphilic\ncomb-shaped polymer, termed PEI-TA, was prepared via a one-step Michael\naddition between low-molecular-weight biodegradable polyethylenimine\n(PEI) and tetradecyl acrylate (TA), followed by neutralization with\nacetic acid. Using the emulsifier PEI-TA, a positively charged avermectin\n(AVM) nanoemulsion was prepared via a phase inversion emulsification\nprocess. Under optimal formulation, the obtained AVM nanoemulsion\n(defined as AVM@PEI-TA) demonstrated exceptional properties, including\nsmall size (as low as 67.6 nm), high encapsulation efficiency (up\nto 87.96%), and high stability toward shearing, storage, dilution,\nand UV irradiation. The emulsifier endowed AVM@PEI-TA with a pronounced\nthixotropy, so that the droplets exhibited no splash and bounce when\nthey were sprayed on the cabbage leaf. Owing to the electrostatic\nattraction between the emulsifier and the leaf, AVM@PEI-TA showed\nimproved leaf adhesion, better deposition, and higher washing resistance\nin contrast to both its negatively charged counterpart and AVM emulsifiable\nconcentrate (AVM-EC). Compared to the large-sized particles, the small-sized\nparticles of the AVM nanoemulsion more effectively traveled long distances\nthrough the vascular system of veins after entering the leaf apoplast.\nMoreover, the nanoparticles lost stability when exposed to multidimensional\nstimuli, including pH, temperature, esterase, and ursolic acid individually\nor simultaneously, thereby promoting the release of AVM. The release\nmechanisms were discussed for understanding the important role of\nthe emulsifier in nanopesticides.