The Influence And Regulatory Mechanism About Wetting And Adhesion Behavior Of Droplet On Target Solid Surfaces By Adding Surfactants

The wetting behavior is the common phenomenon in many daily applications,such as flotation,coating,washing and especially agriculture.Dilute pesticide formulations wet and spread on the leaf surfaces to prevent plants from being attacked by diseases,pests and weeds.However,pesticide and its metabolites are biological toxicity,easy to remain among agricultural products,so there is an increasing demand to reduce their use.The pesticide utilization is about 36.6%in China,because most of them can slide down,bounce or roll off plant surfaces.As a result,the pesticide ends up in the soil,air and water,which causes more environmental pollution.Thus,increasing wettability is believed to be the fundamental and promising approach to decrease pesticide use.In this article,we research the influence of growth period and leaf part on interfacial property of plant leaf surfaces,and the mechanism on the wetting behavior affected by aqueous surfactant solutions.Based on the results,the pesticide additive is prepared to realize the regulation of wetting process,for developing droplet adhesive on plant leaf surfaces.Compared with five smooth solid surfaces,the wetting state is suitable for the Young equation.The driving forces to promoting the molecular adhesion on solid surface are hydrophobic interactions,the Lifshitz-van der Waals interactions and electrostatic interactions,which is decided by the solid surface free energy and its component.When the droplet is infinite close to the solid surface,the adhesive force increases sharply which is better to understand the wetting behavior.At this progress,the surfactant molecules migrate to the solid precursor water film.With the increasing of the concentration,the value increases for better adhere on the solid surface.Meanwhile,the synergistic and antagonistic effects between surfactant affect the wetting behavior.In this research the wetting behavior of nonionic surfactant Triton X-100 on plant leaf surfaces in different developmental stages have been investigated based on the surface free energy,contact angle,adhesional tension and liquid-solid interfacial tension.Meanwhile,the wettability of Triton X-100 is better than those of SDS and DTAB.The results show that the contact angle keeps constant with low adsorption at liquid-air(?LV)and liquid-solid(?'SL)interfaces at low concentration,and the wetting state is in the Cassie-Baxter state because of the roughness.With the increase in concentration,the contact angle decreases sharply because of the ratio of ?'SL to ?LV larger than 1.Meanwhile,the droplet overcomes the pinning effect to display the air among three-dimensional wax layers in the Wenzel state.When the concentration is over CMC,the saturated adsorption film is fabricated at the interfaces and the contact angle keeps constant.For the wheat leaf surfaces,the droplet can progress in the microstructures called hemiwicking because of the capillary effect.However,the rice leaf surfaces are harder to wet and the wetting state occurs when the concentration of Triton X-100 is rather high than CMC.Meanwhile,the adhesion force between the droplet and rice leaf surfaces increases while increasing the concentration,which is conducive to the wetting and adhesion behavior.Based on the mechanism about the wetting and adhesion behavior affected by aqueous surfactantsolutions,the pesticide additive is prepared to realize the regulation of wetting process.In field efficacy trials,the control effect is still over 90%while the pesticide use decreases 25%,for developing droplet adhesive on plant leaf surfaces and reducing the pesticide use.The pesticide additives are likely to be beneficial for protect the environment and food safty.