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Schematic illustration of the fabrication process of angled microfiber arrays and SEM images of the produced fibrillar adhesive. (a) A vertically aligned microfiber array is passed between rollers heated at , while a polyimide (PI) film prevents sample adhesion to the hot rollers. (b) The resulting synthetic fibrillar adhesive consists of an angled microfiber array. (c) Top and (d) side views of the angled fibrillar adhesive.
(a) Evolution of shear force of angled fibrillar adhesive during sliding in the absence of an external normal force. Average (solid line) and standard deviation (error bars) data were obtained from seven tests in which sliding occurred along the microfiber direction. The testing sequence in the multiple-sliding experiment was along (dash-dot line 1), against (dash line 2), along (dot line 3) and, finally, against (dash line 4) the microfiber direction. The inset shows an optical image of contact regions (bright spots) used to estimate the microfiber contact area for sliding along the microfiber direction (scale ). Schematics of an angled microfiber undergoing bending due to sliding (b) along and (c) against the microfiber direction in the absence of an external normal force.
Shear force responses of angled microfiber arrays for sliding [(a) and (c)] along and [(b) and (d)] against the microfiber direction under a fixed normal displacement produced by applying a normal force (preload) of 0.5 and 1 mN, and normal force vs displacement responses of [(e) and (f)] angled and [(g) and (h)] vertically aligned microfiber arrays.
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