Study On Wettability Of Electrostatic Droplets On Hydrophobic Leaves Surface And Dynamic Characteristics Of Impact On Leaves Surface

In the process of electrostatic spraying,it is an important link in the process of plant protection to improve the wetting effect and adhesion of liquid medicine spray on crop canopy.The wetting effect of liquid medicine on crop canopy affects the deposition rate of liquid medicine droplets,which is of great significance to improve the utilization rate of pesticides.Surfactants added to pesticides can improve the wettability of droplets in crop canopy,and also affect the dynamic characteristics of electrostatic droplets hitting crop leaves.（1）In this paper,anionic surfactant sodium dodecyl benzene sulfonate（SDBS）,nonionic surfactant fatty alcohol polyoxyethylene ether 7（AEO7）and mixture of SDBS+AEO7（mass ratio 1:1）were taken as research objects.The changes of surface tension and wettability of droplets on hydrophobic leaves under the action of induced electric field were studied.The results show that the surface tension and contact angle of droplets decrease gradually with the increase of surfactant concentration.With the increase of applied voltage,the surface tension of SDBS+AEO7 mixture drops the most.When the applied voltage is-4k V,The surface tensionγ_120s of SDBS+AEO7 mixture droplets at 120s decreased by about 44.58%compared with that without applied voltage.When the applied voltage is-5k V,The contact angle CA120s of SDBS,AEO7,SDBS+AEO7 mixture drops on the leaves of pepper（the contact angle of drops at 120s）decreased by 14.77%,5.09%and 16.02%respectively compared with the non-applied voltage.The drop rate of dynamic contact angle of surfactant droplets is not only related to the applied voltage,but also closely related to the types of surfactants.When the applied voltage is-5k V,the contact angles CA120s of SDBS+AEO7 mixture droplets on pepper leaf surface and paraffin surface decrease by 16.02%and 5.99%respectively compared with those without applied voltage,so it can be seen that there are differences between paraffin and pepper leaf surface.（2）The conductivity of ammonium glyphosate with different concentrations and the effects of surfactants on the surface tension and wettability of ammonium glyphosate droplets on hydrophobic leaves were studied.The results showed that the surface tension and contact angle of droplets decreased gradually with the increase of ammonium glyphosate concentration.The surface tension of ammonium glyphosate drops increases with the increase of applied voltage,and the surface tensionγ_60s of ammonium glyphosate drops with applied voltage of-5k V（the surface tension of drops at 60s）increases by about 12.0%compared with that without applied voltage.When the concentration is less than 20.00g/L,the contact angle CA60s of glyphosate ammonium drops on pepper leaves decreases with the increase of applied voltage.Compared with no voltage application,the contact angle CA60s of glyphosate ammonium salt drops applied with-5k V voltage on pepper leaf surface and paraffin surface decreased by about 10.18%and 4.89%respectively.Compared with no voltage application,the contact angle CA60s of GR drops（the concentration of ammonium glyphosate,SDBS and AEO7 in the mixed solution is 5.00g/L,0.25g/L and 0.25g/L,respectively）on pepper leaf surface and paraffin surface decreased by about 5.60%and1.80%.When no voltage was applied,the wetting area of GR droplets（6μL）on pepper leaf surface and paraffin surface increased by 3.20%and 2.60%respectively compared with 5.00g/L glyphosate ammonium salt.（3）The experimental study on the movement of deionized water and GR drops hitting the wall was carried out on the visual experimental device of electrostatic drops hitting the wall,and the change of the dimensionless spreading length of the drops during the spreading process was analyzed.The results show that the dimensionless spreading length of GR droplets increases with the increase of impact velocity.When the impact speed is 2.12m/s and 3.05m/s,compared with deionized water droplets,the crown formed by GR droplets hitting pepper leaves is smaller;The dimensionless spreading length of GR drops hitting the wall reached the maximum in 3ms,while that of deionized water reached the maximum in 4 ms.The infinite spreading length of the droplet hitting the wall of Shi Ying is larger than that of paraffin and pepper leaves.During the retraction process after the electrostatic deionized water droplets hit the paraffin surface,the droplets did not rebound.After the electrostatic deionized water drops hit the leaves of pepper,the dimensionless spreading length of the drops increased rapidly with time,and then decreased gradually after reaching the maximum value.