Preparation and characterization of an oil-in-water microemulsion of thiamethoxam and acetamiprid without organic solvent for unmanned aerial vehicle spraying

Spraying pesticides is an essential measure for crop protection in agricultural production process. However, the large organic solvents and surfactants usage of common pesticide formulations have caused concern about environmental pollution. In recent years, unmanned aerial vehicle (UAV) spraying has gained more and more attention because of its ability to reduce the usage of pesticide and replace traditional human-powered spraying equipment. Nevertheless, the potential pollution hazard, spray drift and loss of current pesticide formulations in actual aerial spraying also remain challenging to date. Based on the requirement of appropriative pesticide formulation for UAV spraying, a novel oil-in-water microemulsion of thiamethoxam and acetamiprid without any organic solvents was investigated in this study. Complex emulsifiers were proposed to increase the solubility of pesticides in water, which could avoid the addition of unnecessary organic solvents in microemulsions. The physicochemical properties and application performance of the microemulsions were determined using visual observation, Turbiscan technique, laser particle size, indoor spraying experiments, high-performance liquid chromatography with ultraviolet detection and transmission electron microscopy. The optimal microemulsion with the formulation of 10 % sodium dodecyl sulfate and 10 % fatty alcohol polyoxyethylene ether sulfate consisted of small particles with a mean diameter of 1.9 nm, and exhibited good stability, improved wettability, anti evaporation, and spraying performance with deposition coverage rate of 16.2 %. This study expanded the possibility of the preparation and development of environmentally friendly pesticide formulations applicable for UAV agricultural spraying.