Microscale composite structures towards normal adhesion on skin surfaces
Final Report Abstract
Reversible adhesion is the key functionality to grip, place and release objects non-destructively. Inspired by nature, micropatterned dry adhesives are promising candidates due to their enhanced adhesion compared to non-patterned adhesives. As almost all objects exhibit surface roughness on a scale relevant for van der Waals interactions, roughness induces a dramatic reduction in pull-off stresses and necessarily requires revised design concepts. In our work, we introduced composite pillars, i.e. cylindrical two-phase structures, which are composed of a mechanically stiff stalk and a soft tip layer. The adhesion was found to be affected by the geometry of the composites, material combinations and variations in preload as well as hold time. For example, a smaller layer thickness of the soft tip results in better adhesion performance of the composite structures to smooth and rough substrates due to a reduced magnitude of the edge stress singularity and higher stresses at the center of the contact area related to a confinement effect. Furthermore, we found that the increment of the energy release rate during detachment varies with the extent of confinement. This means that with decreasing film thickness (i.e. larger degree of confinement), the detachment mechanism could change from unstable edge cracks to stable growing finger-like or center cracks. The most striking result of our study is that composite structures with thin, a few ten microns-thick, soft layers exhibited similar adhesion in the presence of finite substrate roughness, whereas adhesion dropped by more than 50% for a conventional pillar structure made from the same soft material. “Composite Pillars with a Tunable Interface for Adhesion to Rough Substrates”: Adhesion Innovation Award 2018 of EURADH and FEICA für R. Hensel.
Publications
- Composite pillars with tuneable interface for adhesion to rough substrates, ACS Applied Materials & Interfaces, 2017, 9, 1036–1044
S.C.L. Fischer, E. Arzt and R. Hensel
(See online at https://doi.org/10.1021/acsami.6b11642) - Numerical study of adhesion enhancement by composite fibrils with soft tip layers, Journal of the Mechanics and Physics of Solids, 2017, 99, 357–378
R.G. Balijepalli, S.C.L. Fischer, R. Hensel, R.M. McMeeking and E. Arzt
(See online at https://doi.org/10.1016/j.jmps.2016.11.017) - Adhesion of a rigid punch to a confined elastic layer revisited, The Journal of Adhesion, 2018
R. Hensel, R.M. McMeeking, A. Kossa
(See online at https://doi.org/10.1080/00218464.2017.1381603)
