| Geckos have attracted widespread attention due to their strong adhesion,easy detachment,dry self-cleaning and long service life.The design of bionic gecko adhesion surfaces based on the multi-level setae structure of gecko feet have huge potential application value in the mechanical grippers,wall-climbing robots,flexible devices,and other fields.However,the existing biomimetic gecko surfaces are prone to local bending or root fracture during multiple reversible adhesion and desorption processes,these phenomena can seriously affect the efficiency and lifespan of bionic surfaces.In contrast to nature,the reversible adhesion and self-cleaning properties of the seta of gecko feet can last up to three months.Therefore,considering the distribution characteristics of components to study the long-term adhesion mechanism of gecko seta,it is beneficial to design and prepare bionic gecko surfaces with excellent self-cleaning and anti-fatigue properties,and is of great significance for expanding its applications in mechanical intelligent manufacturing and biomedical engineering.In this paper,the intrinsic relationship between the composition distribution state and mechanical properties of a single gecko seta was studied,and a long-term adhesion theoretical model based on the composition gradient distribution was proposed.Based on the guidance of the theoretical model,a new generation of bionic gecko surfaces with long service life was prepared.It was proved by experiments that the bionic surface prepared in this paper solved the problems of low self-cleaning efficiency and poor fatigue resistance of the existing bionic surfaces.At the molecular and atomic levels,the intrinsic mechanism of the new generation of biomimetic surfaces with high self-cleaning efficiency and strong anti-fatigue properties is revealed.Finally,a new generation of bionic surfaces is applied to rigid and flexible mechanical clamping devices,which lays the foundation for its application in the field of mechanical clamping.The main research contents and conclusions are as follows:1.The protein components in a single gecko seta were found to have a gradient distribution along the axial direction.Through Atomic Force Microscopy(AFM)tests,it was found that the Young’s modulus of the root of the seta was nearly 20 times higher than that of the top of the seta,which was consistent with the distribution trend of proteins in the seta.The long-term adhesion theoretical model was established by Abaqus and COMSOL simulation,and it was found that when the gradient ratio was 20,the maximum stress of a single gecko seta could be reduced by 50%,while the deflection value was increased by 50%.And under the same stress conditions,the strain value of the bionic surface with gradient distribution of components is more than 58.8%lower than that of the bionic surface with uniform distribution.It shows that the gradient distribution behavior can effectively improve the adhesion between the seta and the contact surface,and the service life of the bionic surface.In addition,the surface force meter(SFA)test found that the adhesion performance of the samples on the hydrophilic surface was generally higher than that on the hydrophobic surface,and the adhesion on the hydrophilic surface could be improved by up to 40%.2.By manipulating the spatial distribution of Fe3O4 magnetic nanoparticles in the polydimethylsiloxane(PDMS)matrix,bionic gecko surfaces with uniform distribution(PDMS-Fe3O4-U)and gradient distribution(PDMS-Fe3O4-G)were successfully prepared by template method.The test results of atomic force microscope(AFM),scanning electron microscope(SEM),Raman spectroscopy,contact angle meter,etc.show that the Fe3O4 magnetic nanoparticles can be distributed in the biomimetic surface random uniform and oriented gradient,respectively.The addition of nanoparticles will not affect the properties of the matrix PDMS,the contact angle of the prepared different types of bionic gecko surfaces is about 135°,which has the similar strong hydrophobic properties as the gecko.3.Through AFM test,it was found that with the increase of Fe3O4 particle content,the Young’s modulus of PDMS-Fe3O4-U bionic surface decreased and the adhesion performance improved.Self-cleaning experiments show that the PDMS biomimetic surface after adding nanoparticles has stronger self-cleaning performance,and the selfcleaning efficiency increases with the increase of nanoparticle concentration,namely PDMS-10% Fe3O4-U(24.6%)> PDMS-5% Fe3O4-U(24.2%)> pure PDMS(23.8%).Combined with density functional theory(DFT),the effect of the addition of iron ions of different valences on the bonding energy of PDMS was analyzed from the molecular atomic scale,and the effect mechanism of the addition of Fe3O4 nanoparticles on the self-cleaning efficiency of biomimetic surfaces was revealed.4.The concentration state and direction distribution of magnetic nanoparticles in the PDMS matrix can be effectively regulated by the induction of an external magnetic field.It is found that the directional rearrangement effect of Fe3O4 particles through magnetophoretic motion can enhance the mechanical properties of the samples.The anti-fatigue experiments show that after 300 anti-fatigue experiments of different types of bionic surfaces,the three biomimetic surfaces of pure PDMS,PDMS-5% Fe3O4-U and PDMS-5% Fe3O4-G can maintain 57%,74% and 90.7% of the initial adhesion,respectively.The biomimetic surface samples with component directional gradient distribution have the best fatigue resistance.Combined with DFT analysis,it was found that the addition of Fe3O4 nanoparticles promotes the binding of iron ions to PDMS molecular clusters,resulting in a gradient-distributed biomimetic surface with stronger anti-fatigue properties.5.A parallel 4-DOF rigid mechanical gripping device was designed and fabricated,and the PDMS-Fe3O4-G bionic surface was applied to the gripper system of the device.Through the stress-strain cloud map analysis simulated by COMSOL,it is proved that the bionic mechanical gripping device has stronger adhesion,grasping and protection performance for fragile and fragile objects.Through the ADAMS modeling analysis of the device,the maximum force and angular velocity in the overall drive joint of the system are only 3.68 N and 15.48 deg/sec,indicating that the designed clamping device has good mobility and stability.Based on the actual clamping device designed and manufactured above,it has successfully realized all-round free grabbing and fixed-point release of objects of different materials(rubber,glass,plastic,steel).6.A strongly hydrophobic bionic gecko surface(PFG)was combined with a hydrophilic hydrogel(PANTFe)to prepare a flexible mechanical clamping device(PANTFe-PFG)responsive to both magnetic and infrared light.Using PANTFe and PFG as the driving system and adhesion system of the flexible mechanical clamping device,respectively,three different types of flexible mechanical clamping devices(single-arm,double-arm,and four-arm)were prepared by optimizing the material and structure of PANTFe-PFG.The results show that the single-arm device can quickly respond to the external magnetic field and realize driving;the double-arm mechanical clamping device can grasp the object when irradiated with infrared rays on the inside for160 s,and can release the object when irradiated on the outside for 140 s.The four-arm mechanical clamping device based on structural optimization has better grasping effect on objects,and can complete the complete grasping and releasing of objects within 120 s of infrared irradiation. |
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