Preparation And Tribological Properties Of Superhydrophobic Surfaces Of Silicon Substrate

Micro-electromechanical systems(MEMS)often use single crystal silicon(Si)as the main structural material.However,due to the microscopic adhesion and wear between micro-components,causing the device to work stability and durability of use.It's a effective way to reduce adhesion and friction that achieve superhydrophobicity on Si surface.The superhydrophobic surface can be prepared by making regular micro-structures and changing the chemical composition.The structural characteristics of SAM can be simulate by the molecular dynamics methods.This paper researched the structural characteristics of N-[3-(trimetho-xysilyl)propyl]-ethylenediamine(DA)-Lauroyl Chloricle(LA)(DA-LA)dual composite self-assembled monolayers(SAMs)on Si surface,and discussed the optimal coverage of DA and LA molecules.When the DA-LA molecules are arranged in orderly on Si surface,DA-LA SAMs molecular model is the most stable.Furthering discussed the wettability of SAMs surface by building nano-droplets to perform 1000ps simulation.The simulation results show that the hydroxylated and DA SAMs surfaces are hydrophilic,the DA-LA SAMs is hydrophobic.The radial distribution function(RDF)shows that there are no hydrogen bonds in the DA-LA dual composite SAMs but the weak Van der Waals force exists between the DA-LA dual composite SAMs surface,of which enhances the surface hydrophobicity.According to the wetting theory,the geometric parameters of the square pillar texture on the superhydrophobic surface of silicon were designed,and the texture preparation was realized by photolithography and inductively coupled plasma etching.Then the wet etching was used to obtain the cavity texture.The morphology and chemical components of the micro-texture was characterized by means of Scanning Electron Microscope and Energy Dispersive Spectroscopy.The low energy of DA-LA dual SAMs were modified on square column and cavity shape textured surfaces,to form a micro/nano composite structure.The chemical components,morphology and contact angle of the SAMs surfaces were characterized by infrared spectrometer(ATR-FTIR),atomic force microscope(AFM)and Contact Angle Measuring Instrument,respectively,and then analyzed the wetting effective regulation by geometrical morphology parameter,further analyzed the surface free energy,the results show that with the micro-texture space increased,the superhydrophobicity increasing,the highest contact angle reached 170.35°.And the lowest surface free energy appeared on DA-LA SAMs,and DA take second place,the highest free energy appeared on hydroxylate surface.The wetting stability of micro-textred superhydrophobic surfaces were researched by exerting horizontal oscillation,increasing droplet volume and drop height.The results show that the wetting state transition didn't occur on the cavity-shaped texture when exerted horizontal oscillation,the wetting stability of cavity-shaped texture better than square column texture when increased droplet volume and drop heightThe AFM microsphere probes were used to measuring tribologically properties of textured Si surface and low surface energy modified textured Si surfaces.The results show that the adhesion of textured Si surface is reduced by 58.4%?63.3%compared to smooth Si,and the friction is reduced by 45.9%-50.3%,the adhesion of Si surface,modified by DA-LA SAMs,is reduced by 68.6%-79.8%compared to the smooth Si,and the friction is reduced by 62.6%-67.5%.It indicates that texture and SAMs-textured Si surfaces exhibit excellent adhesion and friction reduction properties.