Enhanced optimal adhesion using mushroom microfibers

Loading Physical Intelligence Department

Objectives:

In this study, the optimal design of bio-inspired elastomer microfibrillar structures with mushroom-shaped tip endings for maximal adhesion is investigated. Previous works have suggested that a mushroom-shaped microfiber could provide the highest adhesion among many other tip patterns. The optimal shape of the mushroom tip endings is characterized theoretically in terms of stalk diameter (at/a) and the tip ending wedge angle (θ), and verified experimentally with precisely fabricated elastomeric microfibers.

 

Project Members:

Hamid Marvi

Sukho Song

Past Members:

Burak Aksak

Selected Research Results and Papers

The optimal shape of elastomer mushroom-like fibers for high and robust adhesion

Over the last decade, significant effort has been put into mimicking the ability of the gecko lizard to strongly and reversibly cling to surfaces, by using synthetic structures. Among these structures, mushroom-like elastomer fiber arrays have demonstrated promising performance on smooth surfaces matching the adhesive strengths obtained with the natural gecko foot-pads. It is possible to improve the already impressive adhesive performance of mushroom-like fibers provided that the underlying adhesion mechanism is understood. Here, the adhesion mechanism of bio-inspired mushroom-like fibers is investigated by implementing the Dugdale–Barenblatt cohesive zone model into finite elements simulations. It is found that the magnitude of pull-off stress depends on the edge angle θ and the ratio of the tip radius to the stalk radius β of the mushroom-like fiber. Pull-off stress is also found to depend on a dimensionless parameter χ, the ratio of the fiber radius to a length-scale related to the dominance of adhesive stress. As an estimate, the optimal parameters are found to be β = 1.1 and θ = 45°. Further, the location of crack initiation is found to depend on χ for given β and θ. An analytical model for pull-off stress, which depends on the location of crack initiation as well as on θ and β, is proposed and found to agree with the simulation results. Results obtained in this work provide a geometrical guideline for designing robust bio-inspired dry fibrillar adhesives.

B. Aksak, K. Sahin, and M. Sitti, “The optimal shape of elastomer mushroom-like fibers for high and robust adhesion,” Beilstein Journal of Nanotechnology, vol. 5, pp. 630-638, 2014

List of Publications

The optimal shape of elastomer mushroom-like fibers for high and robust adhesion

B Aksak, K Sahin, M Sitti

Beilstein Journal of Nanotechnology 5 (1), 630-638