Dry adhesives containing nonuniform arrays of fibrils were tested for the uniformity of their adhesion strength. These arrays comprised fibrils with nanometer-scale dimensions and lengths tuned from 150 to 1500 nm. The surfaces of the fibrils were rendered hydrophobic through a vapor phase deposition of silane molecules to further tune the adhesion strength of the fibrillar structure. Adhesion force measurements over micrometer-length scales were obtained using a tipless cantilever controlled by a scanning probe microscope. Maps of the adhesion forces depicted diverse variations in adhesion strength with the nonuniform lateral changes in topography. Through an extensive data analysis, differences observed between samples were correlated to changes in processing conditions and surface chemistry modifications. The methods demonstrated in this paper are useful for identifying variations in the adhesion strength of dry adhesives made of nonuniform arrays of fibrils. These advancements are crucial for understanding the correlation between structure and function within nonuniform fibrillar adhesives.
