Anisotropic Stiffness Adhesives for High Shear Forces on Soft Substrates

Abstract

requires two phenomena to take place: contact formation between the adhesive and the substrate and preservation of the formed contact when external loads are applied. [5,6] Consequently, for strong, yet reversible attachment, an adhesive should fulfil two contradictory properties simultaneously: high deformability in the normal direction, leading to a large contact formation, and low deformability in the loading direction, leading to preservation of the formed contact when loads are applied. [7] The presence of such direction-dependent stiffness in a material is commonly referred to as "anisotropic stiffness". [8,9] Dry adhesives are typically patterned with repetitive microscale elements such as pillars, spatulas, or mushrooms. [10-14] Alternatively, patterning adhesives with wrinkles has been proposed for controlling attachment. [15-17] When attaching to hard substrates, such surface (micro)patterns are associated with high adaptability