Adhesives with patterned sub-surface microstructures

Inspired by the complex hierarchical structures found in natural adhesives, we have embedded monolithic stack of several microchannels inside soft layers of silicon elastomers. These channels are rectangular in cross-section and their internal surfaces are textured with microscopic pillars arranged in regular arrays. Displacement controlled indentation experiment on these adhesives shows that adhesion and debonding occur not only on the surface of the adhesive but also at the interfaces of the embedded layers. These textures on the channel surface enhance adhesion via "crack arrest and initiation" mechanism. Furthermore, the adhesive is treated by hydrochloric acid so that the siloxane bonds present on the exposed surfaces are hydrolyzed generating silanol groups which on two contacting surfaces increase the effect of self adhesion hysteresis. Thus, the combined effect of surface texturing is integrated with the chemical treatment to increase adhesion.