Synergetic adhesion in highly adaptable bio-inspired adhesive

Biologically inspired adhesives microstructure requires enough flexibility to make a conformal attachment to the surface as well as high rigidity to maintain the mechanical stability of structure against buckling. To tackle these conflicting factors for the synthetic adhesives is a challenge towards large-scale production and utilizing in practical applications. Addressing this problem, we have fabricated a honeycomb structure with a soft elastic film, partially covering the cavity of the honeycomb pattern. Honeycomb structure provides enough support to maintain the structural stability of the microstructure and soft PDMS film over the pattern provides sufficient flexibility to form a strong attachment with the target surface. Meanwhile, the resemblance of the designed structure to the octopi's sucker generates a negative pressure resulting in suction forces. To justify this suction effect, we compared our results with other controlled honeycomb microstructures (1) without any elastic film (2) with elastic film covering the whole cavity of the honeycomb pattern. Experimental results and theoretical prediction demonstrate the synergistic role of van der Waals and suction forces in the proposed partial-film honeycomb microstructure. The synergistic role of adhesive forces makes this structure a stronger, durable, and surface adaptable adhesive. We also investigated the critical role of the viscous forces for our proposed microstructure in water and silicon oil wetting conditions which signify the contribution of capillary forces.