Atomization Index to Bridge the Physicochemical Properties of Polymer–Surfactant Adjuvants and Multivariate Spray Metrics: Guiding Pesticide Formulation Efficient Design

Pesticide spraying is a primary approach for the chemical management of pests, diseases, and weeds. The efficient design of formulations and their accurate application constitute a systems engineering problem that combines formulation chemistry, application technology, and agronomic practice. The droplet size distribution (DSD), which is determined by the physicochemical properties of the formulation during atomization, has a direct influence on deposition efficiency, drift potential, and control performance. Conventional atomization indicators, such as volume median diameter (VMD), Sauter mean diameter ( D 32 ), and relative span (RS), do not adequately provide a quantitative connection between the physicochemical properties of formulations and the droplet size spectrum needed for effective biological control. A comprehensive atomization quality index that incorporates formulation properties and the optimal droplet size is therefore urgently required. To fill this gap, five atomization parameters, relative diffusion ratio (RD), RS, fractal dimension (FD), drift droplet proportion ( V 150 , ≤ 150 μm diameter), and D v0.5 (also referred to as the VMD), were chosen to construct the atomization bridging index (ABI). The ABI allows a comprehensive quantitative assessment of atomization quality and shows a strong correlation with the physicochemical microstructure of the formulation. The analysis indicates that micelle–polymer complexes generated through polymer–surfactant interactions markedly improve the ABI by jointly lowering dynamic surface tension (DST) and increasing viscosity. The evaluation findings show that the associative polyethylene oxide (PEO)/sodium dodecyl sulfate (SDS) system demonstrates outstanding performance over a broad pressure range. At 250 kPa, the PEO/SDS system at 1× the critical micelle concentration (CMC) reaches the highest ABI value, corresponding to the “Class I (Excellent)” category, and is therefore recommended as the optimal spraying system. Overall, ABI establishes a robust physicochemical-spray linkage framework and provides new guidance for identifying key formulation parameters in pesticide adjuvant design.