Screening structure and predicting toxicity of pesticide adjuvants using molecular dynamics simulation and machine learning for minimizing environmental impacts.

Surfactants as synergistic agents are necessary to improve the stability and utilization of pesticides, while their use is often accompanied by unexpected release into the environment. However, there are no efficient strategies available for screening low-toxicity surfactants, and traditional toxicity studies rely on extensive experimentation which are not predictive. Herein, a commonly used agricultural adjuvant Triton X (TX) series was selected to study the function of amphipathic structure to their toxicity in zebrafish. Molecular dynamics (MD) simulations, transcriptomics, metabolomics and machine learning (ML) were used to study the toxic effects and predict the toxicity of various TX. The results showed that TX with a relatively short hydrophilic chain was highly toxic to zebrafish with LC50 of 1.526 mg/L. However, TX with a longer hydrophilic chain was more likely to damage the heart, liver and gonads of zebrafish through the arachidonic acid metabolic network, suggesting that the effect of surfactants on membrane permeability is the key to determine toxic results. Moreover, biomarkers were screened through machine learning, and other hydrophilic chain lengths were predicted to affect zebrafish heart health potentially. Our study provides an advanced adjuvants screening method to improve the bioavailability of pesticides while reducing environmental impacts.

Salinity-Driven Interface Self-Assembly of a Biological Amphiphilic Emulsifier to Form Stable Janus Core-Shell Emulsion for Enhancing Agrichemical Delivery.

Agrichemical losses are a severe threat to the ecological environment. Additionally, some agrichemical compounds contain abundant salt, which increases the instability of formulations, leading to a lower agrichemical utilization and soil hardening. Fortunately, the biological amphiphilic emulsifier sodium deoxycholate alleviates these problems by forming stable Janus core-shell emulsions through salinity-driven interfacial self-assembly. According to the interfacial behavior, dilational rheology, and molecular dynamics simulations, Janus-emulsion molecules are more closely arranged than traditional-emulsion molecules and generate an oil-water interfacial film that transforms into a gel film. In addition, at the same spray volume, the deposition area of the Janus emulsion increased by 37.70% compared with that of the traditional emulsion. Owing to the topology effect and deformation, the Janus emulsion adheres to rice micropapillae, achieving better flush resistance. Meanwhile, based on response of the Janus emulsion to stimulation by carbon dioxide (CO2), the emulsion lost to the soil can form a rigid shell for inhibiting the release of pesticides and metal ions from harming the soil. The pyraclostrobin release rate decreased by 50.89% at 4 h after the Janus emulsion was exposed to CO2. The Chao1 index of the Janus emulsion was increased by 12.49% as compared to coconut oil delivery in soil microbial community. The Janus emulsion ingested by harmful organisms can be effectively absorbed in the intestine to achieve better control effects. This study provides a simple and effective strategy, which turns waste into treasure, by combining metal ions in agrichemicals with natural amphiphilic molecules to prepare stable emulsions for enhancing agrichemical rainfastness and weakening environmental risk.

Using a Dynamic Hydrophilization Strategy to Achieve Nanodispersion, Full Wetting, and Precise Delivery of Hydrophobic Pesticide.

Various strategies have been developed to improve the applicability of hydrophobic pesticides for better effectiveness in agriculture. However, existing formulations of hydrophobic pesticides still suffer from complicated processing, abused organic solvents, indispensable surfactants, or inescapable ecotoxicity, which strictly limit their applications. Herein, a dynamic covalent bond tailored pesticide (fipronil) amphiphile is constructed to address the above issues, which accomplishes the nanodispersion, full wetting, and precise delivery without organic solvents, surfactants, and materials simultaneously. By introducing a hydrophilic ligand on the hydrophobic fipronil through an imine bond, the cleavable fipronil amphiphile (FPP) exhibits superior water solubility and can even self-assemble into micelles at higher concentrations, which can be directly applied in powder form without organic solvents. Attributed to the suitable hydrophilic/hydrophobic ratio, FPP achieves full wetting and effective deposition on superhydrophobic rice leaves without surfactants. Moreover, benefiting from the unique dynamic nature of the imine bond, FPP maintains good storage stability while sensitively releasing back to fipronil under the humidity and pH trigger, consequently implementing the precise delivery for nontarget Apis cerana and target Chilo suppressalis without materials. To our knowledge, this dynamic covalent bond tailored amphiphile strategy is the first idea that simultaneously takes the dispersibility, wettability, and responsiveness of hydrophobic pesticides into account, providing a possibility to control the entire journey of field application and even promising to be incorporated into the synthesis process, thus paving the way for modern sustainable agriculture.

A facile one-pot route to fabricate clothianidin-loaded ZIF-8 nanoparticles with biocompatibility and long-term efficacy.

BACKGROUND: Neonicotinoids are among the most essential chemical insecticides worldwide because of their high activity against many important pests and wide application. However, their application is limited by their toxicity to honeybees. Therefore, the development of a facile route to fabricate efficient and eco-friendly pesticide formulations is of great significance. RESULTS: In this study, clothianidin-loaded zeolitic imidazolate framework-8 (CLO@ZIF-8) nanoparticles were fabricated by a facile one-pot route using zinc nitrate as a Zn2+ source and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, energy-dispersive spectrometry and Fourier transform infrared spectroscopy. Based on the pH response of ZIF-8, a 'burst release effect' was observed for CLO@ZIF-8 at pH 3 and 5 within 12 h, in contrast to the slow and sustainable release at pH 8. CLO@ZIF-8 improved the retention ability of the pesticide liquid and remained 70% control efficacy on Nilaparvata lugens after water rinsed of sprayed CLO@ZIF-8. The pH response of CLO@ZIF-8 allowed it to maintain 43% control efficacy against N. lugens after 10 days of application, which was twice the efficacy of clothianidin solution (SCA). Moreover, CLO@ZIF-8 reduced the acute toxicity to honeybees (Apis mellifera) by ≥120-fold compared with SCA. CONCLUSION: This study provides new insights into the application of ZIF-8 to neonicotinoids and suggests the need for the development of a biocompatible and eco-friendly pesticide formulation. © 2023 Society of Chemical Industry.

Improved Method to Characterize Leaf Surfaces, Guide Adjuvant Selection, and Improve Glyphosate Efficacy.

Glyphosate, one of the most widely used herbicides, plays an important role in controlling weeds and ensuring crop production. While using glyphosate, adjuvants are commonly added to improve its deposition on weeds and control efficacy. However, changes in weed leaf surface characteristics may reduce glyphosate penetration and contribute to evolved glyphosate resistance. Therefore, it is significant to introduce an improved method for regularizing leaf surface characterization and guide adjuvant selection to improve glyphosate efficacy. In this work, surface characteristics of typical weed leaves have been systematically investigated by 3D surface analysis and scanning electron microscopy, finally quantified by apparent surface free energy (ASFE) due to its comprehensive and quantitative evaluation of leaf surfaces. Moreover, the relationship between the weed leaf surface characteristics and the retention of glyphosate on weeds was established, further related to the control efficacy against weeds. To maximize the utilization rate of glyphosate, the types and concentrations of adjuvants should be regulated according to the ASFE of weeds. Our findings not only regularize the surface properties of weed leaves but also reveal their influencing mechanism on the deposition and biological activity of glyphosate, which provide effective guidance for the use of glyphosate.

Promising Delivery Platform for Smart Pest Control with High Water-Retaining Capacity.

Hydrogels have been extensively used in agriculture to improve crop yields for their excellent properties. However, they are currently used either as pesticide delivery platforms or water retention agents alone; the combination of these two functions into one agricultural hydrogel formulation has never been reported, which is crucial to promote sustainable development in agriculture. Herein, using poly(ß-cyclodextrin) and adamantane-grafted poly(acrylic acid) (PAA-Ada) as the host and guest, respectively, an easy operating, multi-responsive, and safer hydrogel delivery system for insecticides is fabricated by the host-guest interaction between cyclodextrin and adamantane, which can load uniformly dispersed insecticides (fipronil, imidacloprid, and thiamethoxam) up to 60%. Benefiting from the carboxyl and hydroxyl groups on polymer chains, different temperatures (25, 35, and 45 °C) and pH values (5.0, 6.8, and 10.0) change the intermolecular forces within the hydrogel network and then the diffusion of the content, finally resulting in controlled release behaviors. Besides, this platform can rapidly release the insecticides in the presence of amyloglucosidase due to its ring-opening effect on cyclodextrin. Moreover, this platform exhibits high water-retaining capacity toward soil, which can increase the maximum water absorption of nutrient soil and quartz sand by 31.6 and 13.9%, respectively, and slows down the water loss. Compared with commercial formulation, this smart system reduces the acute toxicity to non-target organism earthworms by 52.4% and improves the efficacy against target organism aphids by 47.3%, showing better durability, lower environmental toxicity, and higher efficiency. To our knowledge, this is the first idea that simultaneously adopts the water-retaining capacity and controlled release ability of hydrogels to improve insecticide efficacy. In this regard, this smart hydrogel platform holds great potentials as slow-release granules with water-holding ability for protection against insect pests, providing an alternative platform for the sustainable development in green 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.

Surface properties of Tetranychus urticae Koch (Acari: Tetranychidae) and the effect of their infestation on the surface properties of kidney bean (Phaseolus vulgaris L.) hosts.

BACKGROUND: The wettability of the target surfaces affects the wetting and deposition of pesticides on them. The properties of leaf surfaces change after infestation by Tetranychus urticae Koch. Studying the surface wettability of T. urticae and the changes in leaf wettability after infestation is important to guide the use of acaricides. RESULTS: The body surface of T. urticae is an ellipsoidal crown covered with dense cuticle striations and hairs arranged in different directions, which makes the surface of T. urticae rough and hydrophobic. The abaxial surfaces of the leaves are rougher and more hydrophobic than the adaxial surfaces. After infestation by T. urticae, the faded spots were sunken on the adaxial surface and raised on the abaxial surface, where they had formed new wide peaks and valleys. The adaxial surface became obviously rougher and more hydrophobic, while the roughness of the abaxial surface became slightly larger, and the change in hydrophobicity was not obvious. The contact angles of the studied commercial acaricide on these surfaces were greater than 65° and were affected by the infestation. Reducing the surface tension can allow for better wetting of these surfaces and eliminate changes in leaf wettability. CONCLUSION: The surfaces of kidney bean leaves became more hydrophobic after infestation by T. urticae with hydrophobic surface. The wettability of the acaricide solution should be adjusted according to the changes in leaf wettability. This study has important theoretical guiding significance for improving effective deposition of acaricide.

Bio-based clothianidin-loaded solid dispersion using composite carriers to improve efficacy and reduce environmental toxicity.

BACKGROUND: Neonicotinoids comprise one of the most extensively used classes of pesticides worldwide owing to their broad insecticidal spectrum and excellent biological performance. However, their toxicity to honeybee (Apis mellifera Linnaeus) and silkworm (Bombyx Mori) limits their further application. To address this issue, clothianidin as a model neonicotinoid was developed into a novel controlled-release formulation employing advantaged solid dispersion (SD) technology using composite carriers. RESULTS: In this research, the clothianidin-loaded SD was characterized using integrated methods to elucidate its formation mechanism, showing that clothianidin was embedded into the carrier homogeneously in small crystalline entities. The composite carriers, which are both renewable and environmentally friendly, can significantly prolong the release of clothianidin from seven to 25 days, compared with that of PEG 8000 as a single carrier. Based on the excellent controlled release profiles, it reduced the acute toxicity to A. mellifera and B. mori by 57.68- and 85.32-fold (respectively) compared with that of the conventional formulation. Furthermore, the SD displayed favorable efficacy and persistency against Asian citrus psyllid (Hemiptera: Psyllidae). CONCLUSION: This novel strategy opens up a simple and powerful avenue for improving efficacy and promoting the environmental safety of neonicotinoid insecticides to be used in sustainable crop protection.

Multiple modulations of supramolecular assemblies from a natural triterpenoid-tailored bipyridinium amphiphile.

As the applications of supramolecular assemblies are ultimately inscribed in their nanostructures, strategies that can precisely fabricate and regulate supramolecular architectures from small molecules are of great importance. Herein, in this research multiple modulations of supramolecular assembled structures of a natural triterpenoid-tailored bipyridinium amphiphile, 1-[2-(methyl glycyrrhetate)-2-oxoethyl]-[4,4']bipyridinium bromide (MGBP), have been achieved by adjusting solvents or counterions. Depending on the polarity of solvents, MGBP assembled into nanofibers, helices, pentagon and hexagon microsheets, respectively. Moreover, the nanofibers in methanol/water can transform into ribbons, robust fibers and fiber bundles by addition of counterions with different ionic sizes and valences. This work presents a simple and feasible methodology to modulate assembly structures of a natural triterpenoid-based amphiphile, which may expand the application of natural products in supramolecular materials.

Simple, Effective, and Ecofriendly Strategy to Inhibit Droplet Bouncing on Hydrophobic Weed Leaves.

Despite small-molecule surfactants and polymers being widely used as pesticide adjuvants to inhibit droplet bouncing and splashing, they still have intrinsic drawbacks either in the easy wind drift and evaporation, the unfavorable wettability, or the usage of nonrenewable resources. In this paper, we found that upon droplet impacting, 1D nanofibers assembled from natural glycyrrhizic acid (GL) could pin on the rough hydrophobic surface and delay the retraction rate of droplets effectively. Using GL as a tank-mixed adjuvant, the efficiency of glyphosate to control the weed growth was improved significantly in the field experiment, which addressed the dilemmas of current adjuvants elegantly. Our work not only provides a constructive way to overcome droplet bouncing but also prompted us to verify in future if all 1D nanofibers assembled from different small molecules can display similar control efficiencies.

A simple and effective strategy to enhance the stability and solid-liquid interfacial interaction of an emulsion by the interfacial dilational rheological properties.

The development of an emulsion is an important challenge in many fields, such as agrochemicals, pharmaceutics, paints, cosmetics, inkjet printing, and food science. However, the traditional strategies that refer to the empirical value and complex secondary additives cannot reflect the influence of the structure, content, compound, and adsorption of emulsifiers. Here, we propose a simple and effective strategy to develop the emulsion, wherein the emulsifiers are chosen based on the dilational rheological properties of the interfacial films at the molecular level. The dilational rheological properties of polyoxyethylene (80) castor oil (EL-80), sorbitan monostearate (Span 60), and their emulsions were explored by the oscillating drop method. Based on the dilational rheological properties, the emulsions were prepared by the phase inversion emulsification technique. The results showed that the emulsion was stable and realized effective solid-liquid interfacial interaction, which was attributed to the large dilational modulus (intermolecular interaction) at the oil/water interface and loss modulus (molecular diffusion exchange) at the air/water interface. These factors reduced the Ostwald ripening and coalescence, and finally increased the spreading diameter. Additionally, the prochloraz 25% emulsion in water (EW) and difenoconazole 20% EW were developed to verify the feasibility of the strategy. Therefore, this research advances the understanding of an emulsion by interfacial dilational rheological properties, which can provide a simple and effective strategy to develop a stable emulsion and achieve an effective solid-liquid interfacial interaction of the emulsion.

Wetting and adhesion behavior on apple tree leaf surface by adding different surfactants.

OBJECTIVE: This study was conducted to investigate the wetting behavior of different surfactant solutions on the leaf surfaces of apple during the fruit formation stage. METHODS: Five surfactants, including C12E5, Tween-20, Triton X-100, DTAB, and SDS were evaluated in this study. The contact angle, surface tension, adhesion tension, work of adhesion, and solid-liquid interface tension of droplets on the leaf surface were determined by the drop method. RESULTS: The results showed that the nonionic surfactants C12E5 and Triton X-100 had better wetting effects than other surfactants. Moreover, when the concentration of C12E5 and Triton X-100 was 1 × 10-3 mol/L, the leaves reached a completely wet state. Toxicity measurement showed that the incubation rate of Carposina niponensis eggs decreased gradually with increasing content of C12E5 or Triton X-100. Additionally, field efficacy analysis showed that adding C12E5 or Triton X-100 significantly improved the beta-cyfluthrin 3% water emulsion (EW) against C. niponensis. CONCLUSIONS: These results indicate that the surfactants C12E5 and Triton X-100 can significantly improve pesticide application, which will be helpful for reducing pesticide use and developing new pesticides.

Wetting Behavior and Maximum Retention of Aqueous Surfactant Solutions on Tea Leaves.

In this research, the maximum retention and wetting behavior of surfactant solutions (N-200, N-300, Tween-80, Morwet EFW, DTAB, SDS) on the surfaces of tea leaves was investigated based on surface free energy, surface tension, the contact angle, adhesion work, and adhesion force. The results showed that the contact angles of all surfactant solutions were kept constant with low adsorption at the tea leaf-liquid interfaces below 0.005%. With an increase in concentration, the contact angle of Tween-80 decreased sharply because the adsorption of molecules at the solid-liquid interfaces (ΓSL') was several times greater than that at the liquid-air interfaces (ΓLV). Adhesion work decreased sharply and then reached a minimum at the critical micelle concentration (CMC), but then increased until reaching a constant. Moreover, a high adhesion force did not indicate better wettability, as it does with rose petals and peanut leaves. For tea leaf surfaces, an increase in the contact angle brought about an increase in the adhesion force. In addition, the maximum retention for Morwet EFW is at different concentrations compared to N-200, N-300, Tween-80, DTAB, and SDS, where the maximum retention of Morwet EFW on tea leaves was 6.05 mg/cm2 at 0.005%.According to the mechanisms of wetting behavior on plant surfaces, a recipe for pesticide formulation can be adjusted with better wettability to reduce loss, improve utilization efficiency, and alleviate adverse effects on the environment.

Biobased polymeric surfactant: Natural glycyrrhizic acid-appended homopolymer with multiple pH-responsiveness.

Even though amphiphilic natural products have been widely employed in cosmetics, food, and pesticide formulations, the development of a compound with stimuli-responsiveness is still highly significant. Inspired by the low cost, biocompatibility, pH resistance and amphiphilicity of natural glycyrrhizic acid (Gly), we designed and synthesized an amphiphilic homopolymer, namely, poly(glycyrrhizic acid) (PGly), via reversible addition-fragmentation chain transfer (RAFT) polymerization. The two carboxylic groups on the side chain of PGly promoted it as a multiple pH-responsive polymeric surfactant. As the pH was decreased from 5.0 to 2.0, the PGly transformed from the extension to the coil state and further aggregated into nano/micro particles. During this process, the surface charge, surfactivity and diffusion rate of PGly decreased along with the decreasing pH. Moreover, with ultrasonic treatment (UT), the aggregates that formed at lower pH values decreased (pH 3.0 and 2.0) or almost disappeared (pH 4.0), indicating that these insoluble aggregates at lower pH were broken by UT and were then reassembled into the compacted PGly nanoparticles. Based on the above results, the emulsion (20 wt% xylene) stabilized by 0.1 wt% PGly was fabricated using ultrasonic emulsification for which the diameter distribution and the dispersion state can be reversibly regulated by pH (2.0-5.0). This natural polymeric surfactant exhibited a favorable surfactivity and multiple pH responsiveness in the preparation of emulsions, showing its potential for application in the controlled release of pesticide formulations and in the recovery of organic pollution.

Uptake and Distribution of Fenoxanil-Loaded Mesoporous Silica Nanoparticles in Rice Plants.

Mesoporous silica nanoparticles (MSNs) can be used as carriers to deliver pesticides into plants, which is considered to be one method of improving the efficacy of pesticide usage in agricultural production. In the present work, MSNs with an average diameter of 258.1 nm were synthesized and loaded with Fenoxanil. The structure of the nanocarriers was observed by scanning electron microscopy. The loading content of Fenoxanil-loaded MSNs was investigated. After rice plants in a hydroponic system were treated with loaded MSNs, the concentrations of Fenoxanil in different samples were determined using high-performance liquid chromatography⁻tandem mass spectrometry. The results suggested that rice plants can absorb MSNs from water through their roots, and the dosage has almost no effect on the distribution of Fenoxanil in rice plants. The application of pesticide-loaded nanoparticles in a hydroponic system poses a low risk of Fenoxanil accumulation in rice.

A Natural Triterpene Saponin-Based Pickering Emulsion.

The abuse of chemical surfactants in pesticide formulations is a potential threat to agricultural development and environmental safety. Thereby, developing an efficient eco-friendly pesticide formulation is of great significance. In this research, a biocompatible and ultrastable pesticide formulation has been developed in which merely 1 wt % natural glycyrrhizic acid (GA) was used to emulsify and stabilize 80 wt % agricultural oils. During the preparation process, amphiphilic GA molecules initially self-assembled into 1D nanofibers with a favorable surfactivity, and then afforded GA-based Pickering emulsions with fine droplets. Consequently, the Pickering emulsions transformed into gel-like Pickering emulsions as a result of the formation of a 3D network of nanofibers. On account of the unique chemical structure and admirable assembly behavior of GA, the gel-like Pickering emulsions exhibit ultrastability, thixotropy, and broad pH resistance. In addition, this formulation was investigated for its potential application to pesticides by using pure carbosulfan as the oil phase; up to 60 wt % carbosulfan could be coated, which is more than in the current commercial formulations. This work not only provides new insights into the application of natural biosurfactants to pesticides, but also proposes a biocompatible and eco-friendly pesticide formulation for use in ecological agriculture.

Natural Triterpenoid-Tailored Phosphate: In Situ Reduction of Heavy Metals Spontaneously to Generate Electrochemical Hybrid Gels.

In this work, we reported a biocompatible nature product-based soft material which could convert heavy metals to nanoparticles (NPs) in situ spontaneously in a simple step. We have designed and synthesized a natural triterpenoid-tailored phosphate (methyl glycyrrhetate phosphate (MGP)), and this amphiphilic MGP could form the stable hydrogel and extract gold salt from water, followed by spontaneous in situ AuNP formation without external reductants. Notably, the AuNPs were mainly localized on nanofibers instead of gel cavities, and the resulting MGP-AuNPs hybrid gel exhibited attractive electrocatalytic and conductive properties. In addition, as an efficient leaching extraction agent, MGP hydrogel showed higher affinity toward heavy metals over other common metals on account of the high reduction potential of heavy metals. Our work not only provides a novel yet simple way in generating electrochemical hybrid gels by in situ reduction of heavy metals spontaneously but also expands the application of nature product-based functional materials.

Wettability of pear leaves from three regions characterized at different stages after flowering using the OWRK method.

BACKGROUND: A better understanding of leaf surface wettability is critical to improve the adhesion of liquid pesticides. Leaf surface wettability is dependent on the property of the liquid as well as the physical and chemical properties of the leaf, which vary with climate and growth stage. The aim of this study was to characterize the wettability of pear leaves from three different climatic regions at different stages after flowering. RESULTS: The contact angles of different test liquids were measured on both adaxial and abaxial pear leaf surfaces and the Owens-Wendt-Rabel-Kaelble (OWRK) method was used to calculate surface free energy (SFE) and its polar and non-polar components. The results demonstrated that the SFE of both the adaxial and abaxial surface of the pear leaf, and the proportion of polar component, increased with increasing time after flowering. At early growth stages, pear leaves were highly hydrophobic, similar to a polytetrafluoroethylene surface, whereas at later growth stages, pear leaves were hydrophobic, more similar to a polymethylmethacrylate surface. Also, the SFE differed with climatic region. Factors influencing these changes are discussed. CONCLUSION: Changes in contact angles and SFE correlated with the change of the leaf surface wettability. Leaves became easier to wet (higher SFE), with an overall increasing polar component to the surface, with increasing age after flowering. As expected, changes in wettability were found in pear leaves at different stages after flowering and in different regions (P < 0.05). Pear leaves from Yuanping were easier to wet than leaves from Yuci and Linyi, and adaxial surfaces were easier to wet than abaxial surfaces. These results provide beneficial information for the application of agrochemicals for improved wetting and spreading behavior. © 2018 Society of Chemical Industry.

The wetting behavior of aqueous surfactant solutions on wheat (Triticum aestivum) leaf surfaces.

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 × 10-5 mol L-1. With the increase in concentration, the contact angles of Triton X-100 decrease sharply because the adsorption of molecules at solid-liquid interfaces (ΓSL') is several times greater than that at liquid-air interfaces (ΓLV). With regards to SDS and DTAB, the contact angle also decreases but is even larger than 90° above the CMC, while the ratio of ΓSL' to ΓLV 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.