Optimization Strategy to Inhibit Droplets Rebound on Pathogen-Modified Hydrophobic Surfaces

Mechanism and strategy of self-assembly of quaternary ammonium surfactant molecules to regulate pesticide droplet impact and wetting of hydrophobic surfaces

BACKGROUND

Surfactants regulate the interaction between pesticide droplets and the surfaces of plants on which they are sprayed. The influence of the key structural functional groups of surfactants on the interaction between pesticide droplets and hydrophobic pear leaves has not been explored. The behavior of Imidacloprid (Imid) droplets regulated by cationic quaternary ammonium surfactants with different structures on hydrophobic pear leaves and their bouncing dynamics were studied.

RESULTS

The properties of pesticide droplets regulated by rosin-based bicationic quaternary ammonium salt and ethylene (dodecyl polyoxyethylene/tetradecyl polyoxyethylene) chloride/ammonium bromide were well matched with those of pear leaves with a waxy layer. This structure was closely related to the double-chain structure corresponding to that of double N-head groups in quaternary ammonium surfactants. Quaternary ammonium surfactants regulate the wetting of droplets by forming semi-micellar structures near the three-phase contact line, which drives the droplets to wet and spread on the leaf. The quaternary ammonium surfactant containing the double N-head structure enabled strong wetting and adhesion of pesticide droplets on the hydrophobic surface. The key structural functional groups of different quaternary ammonium surfactants directionally modified the impact kinetics of Imid droplets on the leaf surfaces and their changing trend.

CONCLUSION

The double N-head structure played a key role in the molecular structure of quaternary ammonium surfactants, and the hyperbranched ethylene oxide (EO) chain played a small role in the molecular structure. These results clearly indicate how the structure of key functional groups of quaternary ammonium surfactants regulated the interface adhesion of pesticide droplets on the leaf surfaces and explain the microscopic mechanism of their interaction. © 2024 Society of Chemical Industry.

Bio-based two-dimensional amphiphile with hierarchical self-assembly for enhancing pesticide utilization and reducing environmental risks

BACKGROUND

Biotic and abiotic stresses threaten crop growth and yield. Agrochemicals are an important way to mitigate biotic stress, while frequent low utilization and potential environmental risk affect their sustainable use. In order to improve pesticide utilization, it is common practice to add tank-mix adjuvants by reducing surface tension or forming spherical self-assembly. However, there is a lack of quantitative indicators to screen suitable molecules for sustainable application. In this work, critical factors based on physicochemical properties, and kinetic and thermodynamic parameters are applied to analyze regulatory mechanisms in dynamic processes, and ultimately to establish an integrated strategy for the management of stresses.

RESULTS

Compared with traditional one-dimensional linear amphiphilic molecules, two-dimensional bio-based amphiphilic molecules, especially sodium deoxycholate (NaDC), form self-assembly and could significantly promote the deposition of agrochemical droplets due to maximum energy dissipation. Meanwhile, NaDC increased the inhibition rate of pyraclostrobin against Rhizoctonia solani from 24.4% to about 100.0%, which was beneficial for pesticide resistance to biotic stress. In addition, NaDC could significantly mitigate the harmful effects of salt stress on Oryza sativa by increasing the germination rate of salt-stressed seeds by about 30%, and reducing the environmental risk of pesticides to soil microbial communities for eco-friendly crop protection.

CONCLUSION

Herein, this work demonstrates a sustainable strategy for crop management that enhances the effects of agrochemicals on biotic stresses, mitigates abiotic stresses, and significantly reduces environmental risks. © 2025 Society of Chemical Industry.

Advancement in surfactant-enhanced droplet deposition on the hydrophobic surfaces

Droplets impacting solid surfaces are encountered in nature and industry, from rain to agricultural spraying and inkjet printing. Surfactants are an important factor that affects the impact behavior of droplets. An in-depth knowledge of the influence and mechanisms of surfactants on the dynamics of droplet impact can enhance the precise control of droplets in industrial processes. Herein, recent insights into surfactant-enhanced droplet deposition on hydrophobic surfaces are reviewed. First, the mechanisms of surfactant-enhanced droplet deposition are summarized. Second, the factors that influence droplet deposition, such as molecular diffusion, convective diffusion of surfactants, characteristics of hydrophobic surfaces, and interaction between the surfactant-laden droplets and the hydrophobic surfaces, are explored. Additionally, the influences of surfactants on the spreading and retraction processes of impacting droplets, maximum spreading factor, and oscillation dynamics are reviewed. Finally, typical applications of surfactants in different fields, such as inkjet printing, supercooled surface, and agricultural spray, are summarized, along with challenges and prospects in future research, to provide suggestions for subsequent studies.

Unraveling How Membrane Nanostructure Changes Impact the Eye Irritation of Nonionic Alkyl Ethoxylate Surfactants

Nonionic surfactants used in agri-spraying processes may cause varying degrees of corneal irritation when they come in direct contact with farmers' eyes, and the exact irritations are thought to be determined by how surfactants interact with corneal cell membranes. However, how nonionic surfactants interact with cell membranes at the molecular and nano levels remains largely unexplored. In this study, the interactions between nonionic surfactants (alkyl ethoxylate, C12Em) and lipid membranes were examined by membrane permeability measurement, quartz crystal microbalance with dissipation, dual polarization interferometry, confocal laser scanning microscopy, and neutron reflection, aiming to reveal complementary structural features at the molecular and nano levels. Apart from the extremely hydrophobic surfactant C12E2, all nonionic surfactants studied could penetrate the model cell membrane composed of a phosphocholine lipid bilayer. Nonionic surfactants with intermediate amphiphilicity (C12E6) rapidly fused into the lipid membrane and stimulated the formation of pores across the lipid bilayer, consistent with the cytoplasm leakage and fast cell necrosis observed from the cytotoxicity study of corneal cells. In comparison, while hydrophobic and hydrophilic surfactants [those with long and short ethoxylates (C12E4,12,23)] could cause mild structural alteration to the outer lipid layer of the membrane, these structural changes were insufficient to elicit large cytoplasmic leakage rapidly and instead cell death occurred over longer periods of time due to changes in the membrane permeability. These results reveal the strong link of surfactant-lipid membrane interactions to surfactant cytotoxicity and the association with amphiphilicity of nonionic surfactants.

Self-assembly of eugenol-loaded particles to regulate the adhesion of carriers on leaves for efficient foliar applications and ecotoxicological safety

Currently, there is a pressing need to develop an agrochemical-loaded system that is both uncomplicated and efficient, thereby enhancing the adhesion of agrochemical to leaf surfaces and optimizing their insecticidal efficacy, while concurrently mitigating environmental risks. The flexible eugenol-loaded particles were synthesized via a one-step polyurethane self-assembly reaction, utilizing polyethylene glycol (PEG) as the soft segment and 4,4-diphenylmethane diisocyanate (MDI) as the hard segment. The increase in the length of the soft segment enhances the flexibility of the particles, thereby improving the contact area and adhesion with the foliar surface. When flexible particles are applied on the foliar surface, they can achieve satisfactory resistance to rainfall erosion. When the PEG molecular weight is 800, the residual concentration of eugenol can still reach 42.11% after 6 washes. The carrier protects the active ingredients and improves the resistance to ultraviolet irradiation. After 5 h of ultraviolet irradiation, the concentration of eugenol remained at 59.03% when PEG with a molecular weight of 200 was employed. Greenhouse experiments showed that the flexible transformation of particles greatly enhanced the application effect of spray on the foliar surface of particles. After undergoing three washes, the mortality of the particles can be enhanced by 5.4-8.4 times compared to that of emulsion concentrate (EC) sample. The enhancement of leaf retention performance reduces environmental risks caused by pesticide loss. Meanwhile, the controlled release of particles also reduces the acute toxicity to zebrafish. The toxicity selection pressure of the EUG@P800-Ps sample is 10.6 times that of the EC sample. In conclusion, the preparation process of the system is simple, and the flexible transformation is an effective strategy to improve the foliar application effect of spray and improve the environmental safety.

Hydrophilic and Hydrophobic Surfaces: Features of Interaction with Liquid Drops

The processes of interaction of liquid droplets with solid surfaces have become of interest to many researchers. The achievements of world science should be used for the development of technologies for spray cooling, metal hardening, inkjet printing, anti-icing surfaces, fire extinguishing, fuel spraying, etc. Collisions of drops with surfaces significantly affect the conditions and characteristics of heat transfer. One of the main areas of research into the interaction of drops with solid surfaces is the modification of the latter. Changes in the hydrophilic and hydrophobic properties of surfaces give the materials various functional properties-increased heat transfer, resistance to corrosion and biofouling, anti-icing, etc. This review paper describes methods for obtaining hydrophilic and hydrophobic surfaces. The features of the interaction of liquid droplets with such surfaces are considered. The existing and possible applications of modified surfaces are discussed, as well as topical areas of research.

Coacervate-Enhanced Deposition of Sprayed Pesticide on Hydrophobic/Superhydrophobic Abaxial Leaf Surfaces

Deposition of high-speed droplets on inverted surfaces is important to many fundamental scientific principles and technological applications. For example, in pesticide spraying to target pests and diseases emerging on abaxial side of leaves, the downward rebound and gravity of the droplets make the deposition exceedingly difficult on hydrophobic/superhydrophobic leaf underside, causing serious pesticide waste and environmental pollution. Here, a series of bile salt/cationic surfactant coacervates are developed to attain efficient deposition on the inverted surfaces of diverse hydrophobic/superhydrophobic characteristics. The coacervates have abundant nanoscale hydrophilic/hydrophobic domains and intrinsic network-like microstructures, which endow them with efficient encapsulation of various solutes and strong adhesion to surface micro/nanostructures. Thus, the coacervates with low viscosity achieve high-efficient deposition on superhydrophobic abaxial-side of tomato leaves and inverted artificial surfaces with a water contact angle from 170° to 124°, much better than that of commercial agricultural adjuvants. Intriguingly, the compactness of network-like structures dominantly controls adhesion force and deposition efficiency, and the most crowded one leads to the most efficient deposition. The tunable coacervates can help comprehensively understand the complex dynamic deposition, and provide innovative carriers for depositing sprayed pesticides on abaxial and adaxial sides of leaves, thereby potentially reducing pesticide use and promoting sustainable agriculture.

The simple strategy to improve pesticide bioavailability and minimize environmental risk by effective and ecofriendly surfactants

Low pesticide efficiency has caused serious environmental pollution and economic loss, which are closely related to each link in the targeted delivery of pesticides. However, the existing strategies for improving pesticide utilization rate are not comprehensive, and the regulation of foliar absorption and biological activity has been neglected. As surfactants are the most important agricultural synergists, the impact, wetting, adhesion, and leaf retention behaviors of pyraclostrobin (PYR) droplets containing the surfactant Triton X (TX) series on hydrophobic scallion leaf surfaces were studied. The results showed that TX-102 can sufficiently reduce the splash and roll of droplets when they impact inclined leaves, owing to its low dynamic surface tension. Moderate wetting ability and high adhesion also maximizes leaf retention of the TX-102-added PYR solution sprayed on scallion leaves. Furthermore, TX-102 improved the permeation and absorption of PYR in scallion leaves through the synergistic effects of opening the stomata and dissolving the waxy layer. The synergistic bioactivity of TX-102 against pathogenic fungi Alternaria porri and its safety to non-target organism zebrafish have also been demonstrated. Our study provides a more comprehensive theoretical rationale for screening adjuvants to improve the effectiveness and bioavailability of pesticides and reduce the risk of pesticides entering the environment.

Study on Droplet Impact and Spreading and Deposition Behavior of Harvest Aids on Cotton Leaves

The deposition and spreading of pesticide droplets on the surface of plants is a severe challenge to precise pesticide application, which directly affects the pesticide utilization rate and efficacy. Cotton harvest aids are widely used in machine-picked cotton but the effect of formulation and concentration on the droplet behavior and defoliation effect of cotton defoliants is not clear. To clarify the influence of formulation and concentration on the droplet behavior of cotton defoliants, four formulations (suspension concentrate (SC), water dispersible granule (WG), oil dispersion (OD), and wettable powder (WP)) of cotton defoliants were used to prepare different concentrations of harvest aid solutions, according to the spraying volume. The physicochemical properties, droplet impact, and spreading and deposition behavior were studied. The results indicated that the four kinds of harvest aids have good physicochemical properties and can be wet and spread on cotton leaves. The surface tension of the high-concentration harvest aid solution (the spraying volume was less than 1.2 L/667 m²) was increased, which increased the contact angle and reduced the adhesion tension, adhesion work, and the spreading area. Once the harvest aid solution systems impacted the cotton leaves, it could spread to the maximum in a short time (10 ms). The field experiment showed that the droplet spectrum of harvest aids changed slightly, the coefficient of variation (CV) did not exceed 50%, and the defoliation rate was better when the spraying volume was 1.5 L/667 m². The correlation and principal component analysis showed that the spraying volume (concentration) and coverage were negatively correlated with the defoliation rate, while the viscosity, diffusion factor, and spreading rate were positively correlated with the defoliation rate. Overall, the use of appropriate spraying volume application in cotton fields can improve the performance of spray, increase the effective deposition and wetting spread of defoliants on cotton leaves, further reduce the dosage of defoliants, and improve pesticide utilization. These results can provide a theoretical basis for the scientific preparation and spraying of cotton harvest aid solutions.

Regulating the Entire Journey of Pesticide Application on Surfaces of Hydrophobic Leaves Modified by Pathogens at Different Growth Stages

Under the background of the strategy of reducing pesticide application and increasing efficiency, the mechanism and common technology of efficient and accurate target deposition of chemical pesticides are the key development direction. The interaction between pesticide droplets and a leaf surface affects the deposition behavior of pesticides. However, cucumber leaf surface modified by powdery mildew pathogens at different growth stages is more hydrophobic than a normal leaf surface, which hinders the accurate deposition of pesticides on cucumber powdery mildew leaves. Here, an effective strategy for controlling pesticide efficiency for the entire journey of pesticide application is proposed. Based on the impact dynamics of droplets, the dynamic direction of droplet bounce is determined, the trajectory of droplet rebound is preliminarily determined, and the pinning sites formed by droplets on the surface of cucumber leaves with powdery mildew are confirmed. By analyzing the dynamics in the retraction stage and the energy dissipation rate for droplets after impact, the basic parameters that can be used to simply characterize droplet rebound are screened out, and the effect of addition of an effective surfactant is determined by characterizing the basic parameters (energy dissipation rate, retraction rate, recovery coefficient). The molecular structure formed by the addition of nonionic surfactant in pesticide solution is more appropriate to the interaction between the powdery mildew layer and the pesticide solution, which ensured that the droplets are well wet and deposited on cucumber powdery mildew leaves. Meanwhile, a force balance model for the pesticide droplet wetting state is established to calculate the pinning force for the droplet and predict the transition direction for the droplet wetting state. Impact dynamics combined with force balance model analysis provides a constructive method to improve pesticide utilization during the entire journey for pesticide application on hydrophobic plant surfaces.