Strength, adhesion, and meso-textured surfaces: a tour of size effects in materials and structures

Eduard Arzt

INM – Leibniz Institute for New Materials and Saarland University, Saarbruecken, Germany

One of the central principles in materials science maintains that materials derive their properties at least as much from their microstructure (sometimes called “mesostructure”) as from the bonding between their atoms and molecules. The absolute size scale of the microstructure becomes important as soon as this parameter competes with an internal length, e.g. mean free paths of electrons or phonons, radius of curvature of dislocations, critical crack length, magnetic exchange length etc. Frequently size effects occur as a result of the competition between surface and volume effects. In this talk I will attempt to draw parallels between size effects in the material world and in other, unexpected contexts: central phenomena, which I have studied extensively with students, post-docs and collaborators, are plastic strength of small metal volumes and adhesion of patterned surfaces. In the latter case, we have in recent years developed concepts that explain why the splitting of contacts leads to higher adhesion strengths in biological systems, as e.g. in insects and geckos. We have subsequently emulated this effect in artificial meso-textured surfaces exhibiting unique adhesion properties. Currently, investigations are carried out to allow up-scaling of surface patterning to larger areas. In addition, “smart” surface structures have been demonstrated that allow switching between an “off” and an “on” state upon external stimuli. Thus, the size effect principle is currently being exploited in our laboratory for developing new materials for potential applications e.g. in microfabrication, sports outfits and medical implants.

J.S. KAISER, M. KAMPERMAN, E.J. DE SOUZA, B. SCHICK and E. ARZT, Adhesion of Gecko-inspired biocompatible and biodegradable micropatterned surfaces, J. Art. Organs, in press

D. R. PARETKAR, M. KAMPERMAN, A. S. SCHNEIDER, D. MARTINA, C. CRETON and E. ARZT, Bioinspired pressure actuated adhesive system, Mat. Sci. Eng. C, in press

M. KAMPERMAN, A. DEL CAMPO, R. McMEEKING and E. ARZT, Functional adhesive surfaces with Gecko effect: the concept of contact splitting, Adv. Eng. Mats. 12, 335-348 (2010)

A. S. SCHNEIDER, D. KAUFMANN, B. G. CLARK, C. P. FRICK, P. A. GRUBER, R. MÖNIG, O. KRAFT and E. ARZT, Correlation between critical temperature and strength of small-scale bcc pillars, Phys. Rev. Lett. 103, 105501 (2009)

C. GREINER, R. SPOLENAK and E. ARZT, Adhesion design maps for fibrillar adhesives: the effect of shape, Acta Biomater. 56, 597-606 (2009)

A.V. SPUSKANYUK, R.M. McMEEKING, V.S. DESHPANDE and E. ARZT, The effect of shape on the adhesion of fibrillar surfaces, Acta Biomater. 4, 1669-1676 (2008).

S. REDDY, E. ARZT and A. DEL CAMPO, Bioinspired surfaces with switchable adhesion, Adv. Mats. 19, 3833-3837 (2007).

C. GREINER, A. DEL CAMPO and E. ARZT, Adhesion of bioinspired micro-patterned surfaces: effects of pillar radius, aspect ratio and preload, Langmuir, 23, 3495-3502 (2007).

E. ARZT, S. GORB, and R. SPOLENAK, From micro to nano contacts in biological attachment devices, P. Natl. Acad. Sci. USA 100, 10603-10606 (2003)

Figure: From classical to new size effects – Orowan stress as the epitome of a size effect (upper left, in an ordered compound), thickness-dependent texture in Cu films (upper right) and meso-textured PDMS surface exhibiting size-dependent adhesion.

CV-Eduard Arzt