In this research the wetting behavior of agro-surfactant solutions (Triton X-100, SDS, DTAB) on wheat leaf surfaces have been investigated based on the surface free energy, surface tension, and the contact angle. The results show that the contact angle of those surfactant solutions keeps constant with low adsorption at interfaces below 1 × 10 mol L. With the increase in concentration, the contact angles of Triton X-100 decrease sharply because the adsorption of molecules at solid-liquid interfaces (Γ') is several times greater than that at liquid-air interfaces (Γ). With regards to SDS and DTAB, the contact angle also decreases but is even larger than 90° above the CMC, while the ratio of Γ' to Γ is about 1.20, demonstrating that the Gibbs surface excess is related to the structure of surfactant molecules. Obviously, besides the properties of wheat leaf surfaces and surfactant solutions, the wetting behavior mainly depends on their noncovalent interactions. Among these, the hydrophobic interaction is the main force promoting molecules to adsorb on the surface, with the assistance of the Lifshitz-van der Waals interactions and the electrostatic interactions. According to the mechanism of their wetting behavior on plant surfaces, the recipe of pesticide formulation can be adjusted with better wettability to reduce its loss, consequently improving pesticide utilization and decreasing environmental contamination.

The changes in value of CA and surface free energy (SFE) both reflect the changes of the leaf surface wettability, while the SFE value shows better in wettability characterizing. Obvious rice leaf wettability changes were found on different development stages, which may be beneficial for researches in agrochemical sprays wetting and spreading behavior. Factors influencing these alterations were discussed.

Retention, a crucial process in pesticide application, is heavily affected by the extremely low surface energy and micro/nanostructure of plant leaves. The inadequate retention like bouncing, splashing, and drifting often give rise to severe soil and groundwater pollution. In this article, we present an unprecedented topology-regulation approach that significantly contributes to this issue. A series of pesticide-loaded “hat”-shaped Janus carriers (HJCs) are synthesized via emulsion interfacial polymerization and characterized by scanning electron microscope, thermogravimetric analyzer, energy-dispersive spectrometer, and Fourier transform infrared spectroscopy. Upon spraying on plant leaves, the pesticide-loaded HJCs can embed with the micropapillae and nanosplinters on leaves driven by the “hanger-hat” topology effect, consequently leading to the enhanced retention evaluated by the deposition and flush resistance experiments. Moreover, the release behavior of pesticide-loaded HJCs is found to match the Ritger-Peppas model and finally achieves sustained release. Additionally, the generality of the HJCs synthetic strategy is also studied and applicable to multiple pesticides. This study not only provides a new strategy for increasing pesticide retention on plant leaves but also opens a promising aspect for the applications of Janus carriers in agriculture.

No abstract

The addition of a surfactant is a constructive strategy to enhance the deposition of pesticides on plant leaves in agriculture. However, currently used surfactants normally require to be used at high concentrations, and most of them are anionic or nonionic. In this work, we found that didecyldimethylammonium bromide (DDAB), a double-chain cationic surfactant, can not only inhibit droplets from receding and rebounding but also promote sufficient spreading on paraffin and Chenopodium album L. leaf surfaces at an ultralow concentration (0.05%), in comparison with widely reported sodium dodecyl sulfate (SDS) and bis(2ethylhexyl)sulfosuccinate (AOT). This phenomenon is attributed to the fast adsorption kinetics of DDAB from the bulk to the newly created interface (mere 100 ms), decreasing the surface tension significantly. Field experiments further prove that the addition of DDAB can significantly improve the control efficiency of herbicides. Our findings provide a simple and effective way for improving the droplet deposition on hydrophobic plant surfaces, which may lead to economic and environmental benefits in the future.