Preparation And Mechanism Of Dry-Type Self-Cleaning Surface For Gecko

With the natural evolution of millions of years,organisms have been able to spontaneously evolve complex structures,patterns or textures with versatile features.Of all these features that have been observed,the self-cleaning ability of certain organisms is considered to be the most interesting one.Due to its potential application in various fields,self-cleaning has become the subject of bionics.There is extensive research in such fields as aerospace,energy conversion,and biomedicine and environmental protection.Recently,various in-depth studies have been carried out.Some of the eye-catching biological structures include lotus leaf,sharkskin,butterfly wings and gecko feet.In order to understand and simulate their self-cleaning mechanism better,understanding the attachment and separation of micro/nano materials on the substrate and from the substrate can benefit a wide range of interface sciences.Therefore,we fabricated two AFM tips:a nanosphere tip with 980 nm diameter SiO2 nanoparticles at the AFM tip and a triangular tip truncated tip with 959 nm side length at the tip of the AFM tip.Then we used AFM to study dynamic adhesion enhancement.When the contraction speed increased from 0.02μm/s to 156μm/s,the adhesion of the two tips to four different substrates was significantly increased,and the increase was highest on the sapphire substrate.The order of adhesion of the nanoscale samples（nanosphere tip and truncated tip）of different substrates is:HOPG>silicon wafer>mica>sapphire,which is opposite to the Young’s modulus of the substrate.In addition,the force of truncated tip is greater than the dynamic force at the nanoball end.Therefore,the tip shape and substrate have a significant effect on dynamic adhesion.Besides,Self-cleaning surfaces are desirable for their advantages involving low energy consumption,reusability and sustainability.These types of surfaces have promising applications in vehicle tires,climbing robots,and the aerospace engineering field.Inspired by the gecko’s unique,dry,self-cleaning hierarchical structures,we had fabricated artificial self-cleaning PDMS/Fe₃O₄ composites.The decrease of the degree of polymerization and the energy transference were thought to be the main influence about the improving performance of fiber between PDMS and the Fe₃O₄ magnetic nanoparticles.The pure PDMS surface showed a self-cleaning ability by dislodging24.3%of contaminated particles with only 6 steps.Samples with 5%and 10%of the Fe₃O₄ composite showed a nearly 20%dislodged proportion with only 4 steps and with a flexible mechanical property.Stiffer pillar tips exhibited improved self-cleaning capabilities.This work shows new pathways involving the modulation of surface pillar stiffness and fabrication of self-cleaning surfaces which have applications in the textile industry,robotic industry and tissue engineering field.