Ashutosh Sharma, Ph.D.
Institute Chair Professor
Indian Institute of Technology, Kanpur

Controlling Adhesion by Micro-structures: From Embedded Microchannels to Fractal Surface Textures

Adhesion or the lack of it in nature is controlled by surface texture, as in anti-stick shark skin and in strongly adhering gecko foot. This talk will summarize some of our recent results on the role of adhesion in pattern formation1,2 and the role of surface and sub-surface patterns in adhesion3 of soft elastic surfaces. The surface patterns in an elastomeric film can be spontaneously self-organized by simply bringing it in contact with another surface1 or by application of an external field2 or by its controlled cohesive failure. The resulting surface texture has a profound influence on the adhesive strength of the surface, which can increase or decrease depending on the nature of texture. For example, cohesive failure engenders a multi-scale fractal like texture, thus making non-stick surface of a sticky material. Even more interestingly, adhesive strength can be greatly modulated by imbedding of air pockets and oil filled channels in the interior of a soft elastic film.3 These results show an intimate relation between adhesion and structure at soft interfaces and point to potential technological applications in fabrication of both anti-stick coatings as well as strong, reusable “structural” adhesives3. The structural adhesives harness thermodynamic factors, rather than the kinetic factors such as visco-elasticity, to modulate the adhesive strength. Thus, some structural adhesives are equally effective in wet environments. Further, this approach opens up the possibility of designing ‘smart’ or ‘on-demand’ adhesion.