Adhesion and anisotropic friction enhancements of angled heterogeneous micro-fiber arrays with spherical and spatula tips

Angled polyurethane fiber arrays are modified by adding soft spherical and spatula shaped tips via dipping. These fibers are characterized for adhesion and friction and compared with unmodified fibers and flat material samples. Sphere and spatula tip fiber samples demonstrate increased adhesion, with 10 and 23 times the maximum adhesion of the unmodified fiber sample, respectively. The sphere and spatula tip fiber samples also show increased friction, with 1.6 and 4.7 times the maximum friction of the unmodified fiber sample, respectively. Friction and adhesion are simultaneously observed in a synthetic dry angled fibrillar adhesive sample (spatula tip fiber sample). The direction dependent friction of angled fibers is investigated. The adhesion and friction results reported in this paper suggest that fibers with negligible adhesion can be modified to exhibit both significant adhesion and friction enhancements by the proposed fiber tip modifications.