Study On The Construction And Properties Of Bioinspired Smart Silicone Rubber-based Adhesives

Outstanding adhesion properties of natural structured adhesives,including easy attach/detach,all-terrain mobility,self-cleaning,et al.,have inspired researchers to develop artificial adhesives for diverse applications in daily life.The reversibility and the reusability make the bioinspired smart structured adhesive a hot topic of research.However,it still faces many challenges,for instance,the material fatigue induced by the repeated deformation and the weak adhesion on curved surfaces,hindering the practical applications.Therefore,the thesis here focuses on the design,preparation and application of bioinspired smart polydimethylsiloxane（PDMS）-based structured adhesives,aiming to provide a new design principle for the new generation of bioinspired smart structured adhesives.PDMS is an ideal material to compose the smart structured adhesives,due to its good flexibility,biocompatibility and chemical resistance,light transparency,etc.The mixing of graphene into PDMS offers the graphene/PDMS nanocomposites（GP）the ability to response to external stimuli,like light,electric field and temperature.However,these external stimuli may affect the material properties of GP,like the elastic modulus,which has a great influence on the adhesion of bio-inspired structured adhesives.Here,the dependence of the elastic modulus of properly cured PDMS and GP on the environment temperature has been investigated.For both PDMS and GP,a critical temperature（T_c）has been found.The elastic moduli of PDMS(E_PDMS)and GP(E_GP)are independent of the temperature below T_c.However,E_PDMS and E_GP increases with temperature which is above T_c.It is the result of the entropy elasticity of PDMS and the re-initiated cross-linking of PDMS,which originates from the change of affinity of PDMS chains to the PDMS network and graphene sheet,as suggested by molecular dynamics simulation.Based on the study of the properties of PDMS and GP,a new in-situ smart adhesive is achieved by adjusting the conformations of PDMS chains.The new adhesive,termed as B_GP_P,is composed of GP as the backing layer and PDMS as the micropillar array.The photothermal effect of graphene under UV irradiation heats up the micropillars,resulting in an increase in the chain configurations of PDMS and thus the contact points with counterpart surface.The more contact points in together with the alignment of PDMS chains during shearing result in an adhesion much higher than that without UV irradiation.The adhesion switching thus doesn’t reply on the changing of contact area so that the macroscopic deformation of structures is avoided.Mimicking the unique attach/detach mechanism of gecko toes,a new reversible pillar adhesive with radial-oriented spatular ends（Sr）is prepared by combing the inking-printing-curing technique and the swelling of PDMS.By mimicking the attachment process of gecko toes,the adhesion of Sr is greatly improved compared to the pillar array with single-oriented spatular tip（Ss）and the pillar array with T-shape ends（T-shape）at same size:the adhesion of Sr on the spherical surface with a curvature of 63 m^-1is 3.7 times and 2.2 times than that of Ss and T-shape,respectively.Moreover,by mimicking the detachment process of gecko toes,the Sr can be quickly detached from the spherical surface by the external solvent stimulation.The attachment/detachment process of Sr is completely reversible even under water,indicating a good adhesion stability and reusability.Inspired by the anisotropic friction property of gecko setae and the gait of caterpillars,a footed soft robot（Geca-Robot）with good terrain adaptability and large load carrying capability is designed.Geca-Robot is composed of gecko-inspired triangular micropillars as the feet and alternatively arranged cuboids of PDMS and graphene-PDMS as the muscle.Geca-Robot is remotely powered by light with wavelengths ranging from ultraviolet to infrared,and moves with a caterpillar-like gait.The gecko-inspired feet allows Geca-Robot to unidirectionally travel on terrains of varying roughness,slope,and degree of dryness at a wide working temperature range（-17 to 100°C）.The assembly of feet and muscle allows Geca-Robot to move by a caterpillar-like gait,in confined narrow spaces,and to carry heavy loads weighing approximately 50 times its own mass.