Buckling-Based Strong Dry Adhesives Via Interlocking

High-aspect-ratio shape-memory polymer (SMP) pillar arrays are investigated as a new type of dry adhesive based on buckling and interlocking mechanism. When two identical SMP pillar arrays are engaged at 80 degrees C, above the glass transition temperature at a preload larger than the critical buckling threshold, the pillars are deformed and become interweaved and/or indented with each other. After cooling to room temperature, strong pull-off forces are observed in the normal and shear directions, both of which are much larger than those from pillar-to-flat surface and flat-to-flat surface contact. From finite element anaylsis (FEA) and comparison of measured and calculated adhesion values using different contact mechanics models, it is shown that interweaved pillars are the main source that contributes to the pillar-to-pillar adhesion and the indented pillars set the lower limit, whereas the probability of interdigitation is very low. Further, it is found that interweaved pillars are primarily responsible for the decreased adhesion strength and increased anisotropy when the pillar spacing became larger. Finally, it is shown that the bonded pillars can be easily separated after reheating to 80 degrees C due to significant drop of modulus of SMPs.