The Study On Anti-frictional Mechanism Of Carnivorous Plant Nepenthes Alata And Bionic Fabrication

Issues of wear,high temperature,adhesion and energy consumption caused by friction have tremendous adverse effects on energy,environment,technology and economy in today’s world.Billions of dollars of huge wastes have been produced every year.Adhesive wear is one of the most common forms of wear and widely exists in many engineering fields,e.g optoelectronics,electronics,energy,machinery and aerospace.A number of attempts,such as selecting wear-resistant materials,surface strengthening technique or heat-treatment,adding lubricant to friction interface,have been made to reduce adhesive wear.However,none of these methods have achieved desirable effects due to their complicated processes and high costs.Therefore,it has been becoming difficult but still urgent to obtain novel anti-adhesive wear.Nepenthes Alata was chosen as the study object.The anti-frictional mechanism of the peristome and slippery zone was studied and bionic fabrication was carried out.The two-dimensional and three-dimensional surface morphologies and chemical compositions of the peristome and slippery zone were systematically studied using scanning electron microscopy(SEM),laser confocal microscope(LSM)and superdepth microscope.Based on the Cassie-Baxter model,the mathematical contact angle model of slippery zone micro-nanostructure parameters was established.Meanwhile,the anti-adhesion law on the surface of the Nepenthes Alata was explained by the ant slide test.Finally,based on the above research results,the biomimetic anti-frictional surface was fabricated by laser biomimetic coupling technology,anodization and plasma treatment.The tribological properties of the biomimetic surface under different lubricating media were studied using universal micro-tribology UMT-5.The main conclusions are as follows:(1)The two-dimensional and three-dimensional surface morphologies and chemical compositions of peristome and slippery zone were systematically studied.It was found that peristome is constituted by two-order microgrooves,and there are about ten second-order microgrooves distributing on each first-order microgrooves.Meanwhile,there are microcavities were contained in ten second-order microgrooves.For the slippery zone,there are plenty of inhomogeneously distribute anisotropic lunate structures,which approximately orient to the pitcher bottom.The surface roughness,height and density of lunate structure decrease from top to bottom,and its size of surface structure is related to growth period.The three-dimensional plate-like wax crystals in the hydrophobic slippery zone and the lunate structure constitute of micro-nano hierarchical structure.FTIR results shows that chemical compositions of peristome and slippery zone under different growth period are basically similar.(2)The result of wettability test shows that peristome is superhydrophilic,which contributes to lock liquid and form a liquid film.The static contact angles decreased from top to bottom in slippery zone.The static contact angle in the uppermost region of the slippery zone is 156.1°,and its sliding angle is about 0°,which demonstrate the hydrophobicity.In the combination with the changing tendencies of the contact angle,density and surface roughness,the density of lunate structure affect contact angle by changing the surface roughness.The contact angle of de-waxed slippery zone is 129°.It shows that the wax crystal plays an important role in wettability of the slippery zone.It indicates that the difference of wettability is controlled by lunate structure,and wax crystal is the key to getting large contact angles.Based on the Cassie-Baxter model,the mathematical contact angle model of slippery zone micro-nanostructure parameters was established.The effect of lunate structure and wax crystal on wettability was further proved by the mathematical model.(3)The result of ant slide test shows that the slippery zone has low friction.The surface area is greatly reduced by the nanoscale roughness of the surface waxy crystal,which greatly reduce the friction.The peristome can slip ants mainly because the surface is infiltrated with a liquid film to form lubricating friction.(4)The result of friction test shows that friction coefficients of peristome and slippery zones were lower than that of the polished plane,indicating that peristome and slippery zones have excellent anti-frictional performance.(5)Based on the research of surface morphology and tribology performance,the relevant parameters of shape,structure and size were extracted.Through the optimization of the size and structure,seven different biomimetic surfaces were prepared by laser process.Meanwhile,the biomimetic surfaces were modified by anodic oxidation and plasma treatment to get different surface wettability.Dry friction test shows that the friction coefficient increased and then decreased with the increase of distance of lunate structure.The friction coefficient is the lowest when the distance of lunate structure is 240μm×165μm.Meanwhile,the friction coefficient of the microstructure surface is lower than that of flat surface in the condition of oil lubrication,grease lubrication,water lubrication or dry friction.The friction coefficient of superhydrophobic surface treated by anodic oxidation was lower than that of superhydrophilic surface treated by plasma,which confirms that the stronger the hydrophobicity,the smaller friction coefficient of the surface.