Study On The Deposition Law And Regulation Mechanism Of Pesticide Emulsion Droplets On Rice Leaves

Pesticide-to-target dose transmission involves three drug-carrying systems:formulation,solution,and atomization,which are affected by multiple factors such as the characteristics of the pesticide,spraying equipment,and the leaf structure.At present,about 80%of pesticides are processed into dosage forms that are diluted with water and sprayed,and most of the secondary dispersion solutions of pesticides are emulsion pesticide-carrying systems.After the pesticide solution is atomized by the spraying device,it will suffer loss behaviors such as bounce and splash during the transfer to the leaf surface.In particular,the super-hydrophobic interface characteristics of the rice leaf surface and the complexity of the paddy field environment result in low utilization of pesticides in the paddy field.With the development of new plant protection technologies,how to organically integrate the development of formulations with the application equipment,the physical and chemical properties of the active ingredients,and the characteristics of the target leaf surface,study the deposition law and regulation mechanism of droplets on the leaf surface of rice,and improve the pesticide droplets effective deposition on the target interface is an important scientific problem.Based on the above scientific issues,the main achievements are described as follows:1.Established a microscopic evaluation method for the stability of pesticide emulsions,and increased the understanding of emulsion formation and stability mechanismsEmulsion stability is a key physical characteristic in the preparation and use of emulsions.In this study,the interaction forces between two droplets in different solutions were measured by a modified DCAT21 tensiometer equipped with a high-frequency digital camera which can capture the droplets coalesce process and correspondingly force curves at the same time.The results indicate that for pure surfactant solution,only when the concentration exceeds the critical micelle concentration,sufficient surfactant molecules are adsorbed on the oil-water interface to form a high-strength interface film,so as to prevent droplet coalescence and improve the emulsion stability.However,for pesticide solution,the active ingredient with a certain surface activity will reduce the interfacial tension of the solution.We also found that the active ingredient and surfactant molecules exhibit competitive adsorption in the same phase and mixed adsorption in different phases,which have different effects on the emulsion stability.This study compared the stability of the pure surfactant solution and pesticide solution through microscopic observed the change of force and the coalescence phenomenon in the dynamic process of droplet contact which can advance our understanding of the mechanism of the emulsion stability.2.Prepared the water-in-oil emulsion system of isoprothiolane and studied the deposition law and regulation mechanism of droplets on the rice leaf surfaceBased on the requirements of aerial spraying special formulations,the solvent and emulsifier were screened to prepare water-in-oil emulsion of isoprothiolane,and the stabilities of the resulting emulsions were characterized using a Turbiscan Lab^Expertwith a thermostatic system.The physical-chemical properties of the water-in-oil emulsion were determined using the respective Collaborative International Pesticides Analytical Council（CIPAC）methods.The results indicated that the water-in-oil emulsion of isoprothiolane with the advantages of environmental-friendly,stabilization,and high efficiency is prepared by the environmentally friendly,high boiling point,heavy aromatic solvent S-200 and the polymeric emulsifier A-7.The polymer emulsifier A-7 promotes the stability of the water-in-oil emulsion better than the conventional surfactant.The water-in-oil emulsion represented an improved dosage form in terms of pesticide properties:oil as the continuous phase of the water-in-oil emulsion has better anti evaporation performance,and the stable water-in-oil emulsion can reach the foliage and spread quickly,which can improve the deposition on target.This study provides valuable information for the use of water-in-oil emulsion for a wide range of applications,especially in UAVs without dilution.In addition,a high-speed camera was utilized to visualize the bounce behavior of droplets of different pesticide solutions on rice leaf surfaces.We explored the addition of surfactants to different pesticide solutions and altered a pesticide solution system to prevent or regulate droplet bounce behavior.Experimental results indicate that the addition of surfactants to a pesticide solution can inhibit the bouncing of droplets on rice leaf surfaces（～30 ms）.Additionally,a water-in-oil emulsion can not only significantly inhibit droplet rebound on a superhydrophobic surface,but also quickly and automatically spread（～10 ms）pesticide droplets to maximize the wetting area.Therefore,this work effectively improves the utilization of pesticides and reduces environmental pollution.Moreover,the wetting behavior of two types of pesticide formulations prepared by oil-based solvent on the rice leaf surface was investigated based on the surface free energy,surface tension,contact angle,adhesion tension,and adhesion work.The interfacial dilational rheological properties of different pesticide solutions are measured as a function of concentration.This study clearly demonstrates the fact that water-in-oil emulsion has a better wettability than oil-in-water emulsion,especially as the concentration increases,the leaves reach a completely wet state.Compared with the vegetable oil（methyl oleate）,the mineral oil（solvent oil No.200）has smaller dilational modulus and surface tension,showing excellent wetting properties.The water-in-oil emulsion prepared with solvent oil No.200 has the smallest dilational modulus,and the spray droplets spread rapidly to the maximum wetting area on the rice leaves,which can be used in ultra-low volume spray.We proposed a new way to enhance the droplet deposition on target leaf surface by changing the properties of pesticide formulation and directly or in low dilution to spray.In addition,it is a simple method to select suitable concentration and formulation by evaluating the interfacial dilational rheological properties of pesticide droplets.The results provide new insights on how to increase the deposition of droplets on superhydrophobic leaf surfaces by screening formulations and concentrations.3.Prepared the oil-in-water Pickering emulsion system of mefentrifluconazole and studied the deposition law and regulation mechanism of droplets on the rice leaf surfaceFor the green development of pesticide industry,it is highly desirable to reduce the dosage of surfactant and increase the effectiveness of pesticides,it is necessary to develop new pesticide formulations with good environmental compatibility.Herein,flowers-like Zn O particles were fabricated via a simple precipitation method at room temperature,which was chosen as novel Pickering stabilizers for the emulsion in view of their economically feasibility,antibacterial and environmentally sustainable features.Mefentrifluconazole has good solubility in the pine oleoresin-based plant oil ND-60 that is a safe,environmentally friendly and renewable pure plant-based green solvent,which selected as the oil phase.A novel Pickering emulsion with the water phase fraction of 70 vol%can be easily prepared using 0.5 wt%Zn O particles and 0.1wt%A-7 as a dual emulsifier,which can reduce the dosage of conventional surfactants.Simultaneous adsorption of Zn O particles and A-7 at the oil-water interface in the form of a densely packed layer make a synergistic effect,preventing droplet coalescence by a steric mechanism.In addition,the flowers-like Zn O particles can be inlaid and adhered to various micro-nano structures on the surface of rice leaf.Due to the friction between each other,it has better deposition performance.The Pickering emulsion effectively inhibits droplet rebound and deposited on the rice leaf with different inclination angles in 1.5 ms,and then spread to the maximum wetting area within 360 s,thereby improving the efficacy of pesticides and reducing environmental pollution.This study provides a new opportunity for the application of multifunctional Zn O particles and holding great promise for preparing pesticide formulations in modern and environmentally friendly agricultural applications.In summary,this study uses qualitative and quantitative methods to deepen the understanding of the mechanism of pesticide emulsion formation and stabilization from a microscopic point of view,and provides theoretical guidance for pesticide research and development and application.Based on the physical and chemical properties of isoprothiolane and mefentrifluconazole,combined with the application method and the micro-nano structure of the rice leaf surface,and designed an efficient emulsion pesticide-carrying system to deepen the formation of pesticide formulations.Study and recognize the interfacial behavior laws of different emulsion pesticide-carrying systems on rice leaf surface wetting,spreading,and bounce process,reduce the bounce loss of droplets on rice leaf surface,and increase the retention;Explore and clarify the key theoretical methods and regulation mechanisms for increasing the effective deposition of droplets on rice leaves,and provide scientific theoretical guidance for the development and application of pesticides.