Study On Water-Solid Contact Electrification In Droplet Impacting On Polymer Surfaces By Plasma Nanotexturing

Plasma surface treatment technology is an extremely effective method for surface modification of polymer materials.Through the plasma etching process and plasma polymerization process,the nanostructure and chemical composition of the polymer material surface can be changed,so that the surface can obtain super-hydrophobic,self-cleaning,anti-adhesion and other properties,which is widely used in industrial production,biomedicine and other field.Studies have found that interfacial charge separation occurs when droplets impact superhydrophobic surfaces superhydrophobic properties.However,there are relatively few studies on interfacial charge separation in droplet impacting on superhydrophobic surfaces with different nanostructures,so this article focuses on interfacial charge separation in droplet impacting on textured superhydrophobic surfaces.In this paper,by changing the oxygen plasma etching time and the octafluorocyclobutane plasma polymerization time,polymer surfaces with different nano-textures are prepared,such as polypropylene.Using scanning electron microscope(SEM),electrometer,contact angle measuring instrument and other analytical instruments,the morphology of the plasma textured surface,the solid-liquid contact charge and the wettability of the contact charged surface are analyzed,respectively.After,by impacting different numbers of droplets on the surface,a channel with a gradually increasing amount of charge is designed on the surface basing the charge accumulation effect,which realizes the spontaneous directional transmission of the droplets on the surface,and explores the factors that affect the speed of the droplets.The results show that,as the oxygen plasma etching time increases from 3 min to 20 min,the length of the nanowires on the polypropylene surface increases,and the nanostructures density of the polypropylene surface etched 3 min is greater than that of the surface with etching for 20 min.When the droplet impacts different sizes nanostructures of the polypropylene surface,the impact height droplet to the surface is 40 mm,the projected charge density of the short nanowire surface is greater than that of the long nanowire surface,and the charge amount of a single nanowire is smaller than that of the long nanowire surface.However,since the surface nanostructure density of short nanowires is greater than that of long nanowires,the actual solid-liquid contact area increases and the surface charge density increases.When the plasma deposition time of octafluorocyclobutane was increased from 1min to 20 min,the nanowire structure transformed into nanopillar structure,so the height and spacing of the nanostructures decreased,and the bottom diameter increased.When droplets impact different nanostructures of the surface,the projected charge density of the nanopillar structure surface is greater than that of the nanowire structure,and the charge value of a single nanostructure hasn't significant change.Since the diameter of the nanopillars is larger than that of the nanowires,the actual solid-liquid contact area increases and the surface charge density increases.When the plasma treatment time is constant,change the polymer type of the base material,due to factors such as the distribution of crystal regions of different polymers,defects,and the difficulty of etching,the nanotextures prepared on the surface are different.The surface of PET and PMMA has a nano-cluster structure,and the surface of PTFE has a nano-cone structure.When the droplets impact the surface of different materials,the difference in surface charge density is small.In addition,the surface charge will reduce the surface tension of the interface liquid and increase the solid-liquid contact area,thereby reducing the surface contact angle and increasing the rolling angle.On the basis of understanding the surface charge generation and its influence law,the spontaneous directional transport of liquid droplets on the surface is realized by controlling the surface charge.According to the moving speed of the droplet on the surface,the moving speed of the droplet on the long nanowire of the surface is faster than that of the short nanowire,and the moving speed on the nanopillar structure of the surface is lower than that of the nanowire structure,and the moving speed of the droplet on the surface of the long nanowire is the largest,which is 91 mm/s.In addition,when the volume of the impact droplet or the impact height of the droplet is increased,the surface charge density increases after impact,and the movement speed of the droplet on the surface becomes faster;when droplets of Na Cl solution are used to impact the surface,as Na~+shields the negative surface charges,the surface charge density decreases and the movement speed of the droplet becomes slower.