Abstract
The adhesion behavior of elastomeric nanofibers was examined by a contact-mechanical approach using a Johnson–Kendall–Roberts (JKR) instrument. A nanofibrillar elastomer substrate was fabricated by replicating crosslinked polydimethylsiloxane (PDMS) from an anodic aluminum oxide (AAO) template. The adhesion behavior of a regular hexagonal array of PDMS nanofibers formed over a wide range was investigated using soft and stiff hemispherical probes, which were prepared using PDMS and polystyrene (PS), respectively. The intrinsic work of adhesion (W) of the elastomeric nanofibrillar substrate was observed to substantially decrease, which was more prominent for the less deformable PS probe, revealing a reduction in the real contact area. Meanwhile, the adhesion energy (G) in the dynamic state with increasing separation rate was greatly affected by the deformation of nanofibers. The energy-dissipation factor for the nanofibrillar surface was far larger than that for the flat surface, and this difference was more significant for the case of contact with the deformable PDMS probe. This resulted in a great increase in the adhesion energy, making it even larger than that of the flat surface, overcoming the reduction in the real contact area.
Highlights
INTRODUCTIONAdhesion measurement has been widely performed under the experimental geometry based on contact mechanics theory,[1] that is, the contact between two spheres (or equivalently, two cylinders or a sphere on a flat surface) using an atomic force microscope (AFM), a Johnson–Kendall– Roberts (JKR) apparatus, and a surface force apparatus (SFA), etc
Adhesion measurement has been widely performed under the experimental geometry based on contact mechanics theory,[1] that is, the contact between two spheres using an atomic force microscope (AFM), a Johnson–Kendall– Roberts (JKR) apparatus, and a surface force apparatus (SFA), etc
We report the adhesion behavior of elastomeric nanofibers using the JKR technique in both equilibrium and dynamic conditions
Summary
Adhesion measurement has been widely performed under the experimental geometry based on contact mechanics theory,[1] that is, the contact between two spheres (or equivalently, two cylinders or a sphere on a flat surface) using an atomic force microscope (AFM), a Johnson–Kendall– Roberts (JKR) apparatus, and a surface force apparatus (SFA), etc. Dominant adhesion mechanism of geckos is purely the van der Waals interaction.[11,12] Thereafter, there have been several reports on the adhesion behavior of synthetic gecko foot-hair Their conclusion is usually that the adhesion strength of each nanofiber is roughly in the range of the van der Waals force.[13,14,15,16] The JKR theory has been used to describe the contact of fibrillar structures. This theory relates the interfacial-force-induced contact deformation to the thermodynamic or intrinsic work of adhesion (W ) between solids and provides a theoretical basis for experiments designed to directly measure the surface and interfacial energies of solids. The deformation of a nanofibrillar surface involved in dynamic adhesion is studied by investigating its contact behavior with both soft (deformable) and stiff (non-deformable) solids under various test rates
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