Funnel-shaped microstructures for strong reversible adhesion

The potential of a new design of adhesive microstructures in the micrometer range for enhanced dry adhesion is investigated. Using a two-photon lithography system, complex 3D master structures of funnel-shaped microstructures are fabricated for replication into poly(ethylene glycol) dimethacrylate polymer. The diameter, the flap thickness, and the opening angle of the structures are varied systematically. The adhesion of single structures is characterized using a triboindenter system equipped with a flat diamond punch. The pull-off stresses obtained reaches values up to 5.6 MPa, which is higher than any values reported in literature for artificial dry adhesives. Experimental and numerical results suggest a characteristic attachment mechanism that leads to intimate contact formation from the edges toward the center of the structures. van der Waals interactions most likely dominate the adhesion, while contributions by suction or capillarity play only a minor role. Funnel-shaped microstructures are a promising concept for strong and reversible adhesives, applicable in novel pick and place handling systems or wall-walking robots.