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Bioinspired Nanopatterned Adhesives via Colloidal Surface Assembly

Marleen Kamperman Wageningen University, Physical Chemistry and Colloid Science, Wageningen, Netherlands

Many animals have evolved adhesive organs on their feet enabling them to strongly attach to and quickly detach from nearly any kind of surface. These organs come in two basic designs : (1) pads densely covered with micro- or nanosized fibrils (“hairs”) with a wide variety of tip shapes observed in e.g. spiders, geckos, beetles, and flies, and (2) pads with macroscopically smooth surface profiles, observed in e.g. tree frogs, ants and grasshoppers. Regardless of the design, both types use non-covalent surface forces to achieve adhesion, and research suggests that they rely primarily on van der Waals forces. The surface structure, not the chemistry, is therefore dominating the function of natural adhesive systems.
We developed a nanofabrication process based on colloidal self-assembly, which allows the fabrication of elastomers patterned with nanodimples. Close-packed monolayers at the air/water interface were used as a template for the elastomer without the need to transfer the monolayer to a solid substrate. The subphase was used to systematically tune the order of the colloidal monolayer and to change the immersion depth of the particles. This led to direct control over the topography of the elastomer surfaces. Compared to smooth interfaces, adhesion of these nanopatterned surfaces was enhanced, which is attributed to an energy dissipating mechanism during pull-off. All nanopatterned surfaces showed a significant decrease in friction in comparison to smooth surfaces.