Effect of carbon chain length of cationic surfactants on regulating droplet behavior on peanut leaves.

Background: Droplet rebound on superhydrophobic leaves during pesticide application significantly increases pesticide waste and decreases application efficiency. An appropriate surfactant is crucial for suppressing droplet rebound and enhancing wetting and spreading on leaf surfaces.

Results: The rebound, wetting and spreading behaviors of cetyltrimethylammonium bromide (CTAB) series of surfactants with varying different carbon chain lengths (n = 6-16) were evaluated on peanut leaves. Aqueous solutions of CTAB-CTAB were prepared, their physicochemical properties were assessed. The surface properties of peanut leaves and droplet impact, wetting, and spreading behaviors were also tested.

Conclusion: At equivalent concentrations, shorter-chain surfactant molecules were less effective at forming likely micellar aggregates that suppress droplet rebound. However, as chain length increased, the wetting and spreading rate of surfactant molecules improved, resulting in reverse wetting and suppressing bouncing. Furthermore, the impact of leaf micro/nanostructures and charge properties on the wetting behavior of different surfactant droplets was elucidated, revealing factors underlying the enhanced retention quantity and poor wetting and spreading of the CTAB series. These findings may aid in reducing pesticide waste and provide multidimensional support for the precise control of droplet behavior in different scenarios and during CTAB application. These findings hold substantial value for future agricultural spraying applications, especially for unmanned aerial vehicle plant protection. © 2025 Society of Chemical Industry.