A New Concept for an Adhesive Material Inspired by Clingfish Sucker Nanofilaments.

Underwater adhesive materials are in high demand in various fields, and fish species with sucker disks have attracted attention due to their superior performance and interesting structures. The clingfish, in particular, is widely known for using hierarchical sucker disk structures to demonstrate rapid and strong adhesion to rocky surfaces under strong currents. We examined the combination of nanofilaments and mucus in the clingfish sucker disk. Nanofilaments reinforce mucus adhesion force by reducing the compliance without affecting the contact area. We prepared structures from hard polymers and soft polydimethylsiloxane (PDMS) that mimicked clingfish sucker nanofilaments and mucus, with these biomimetic structures showing significant adhesion force underwater. Furthermore, the hardness and length of the nanofilaments and Young's modulus and thickness of the mucus-mimicking PDMS layer had critical effects on the adhesion force. According to the results, clingfish nanofilaments act as hard bracing for the soft mucus, and the structural combination of the conflicting characteristics of hardness and softness, thus achieved, is crucial for strong adhesion.

Effect of the Microstructures on Vulcanized Rubber Frictions.

Vulcanized rubber is widely used in a wide range of applications because of its flexibility, durability, sealing properties, and high degree of friction. However, this high degree of friction can also become an issue, as it leads to the wearing and breakage of parts. In this report, we investigated the effects of the vulcanized rubber microstructures on friction force by using simple, anisotropic microstructures. The line and space master microstructures were prepared from a photoresist, and the structures were transferred to PDMS, PSt, and then Ni. After surface modification of the Ni microstructures by TEOS, the vulcanized rubber microstructures were fabricated by a simple hot press process with the TEOS-coated Ni microstructure molds. The structural parameters of the vulcanized rubber line and space microstructures were found to be successfully varied by elongation, and the structural deformations were also investigated by FEM simulations. Measurements of the frictional force of the vulcanized rubber microstructures revealed the friction coefficient was reduced by the surface microstructures and was affected by the directions of the contact because of the microstructure anisotropy. The reason for of these results can be explained by the changes in the contact area and hysteresis friction. These results suggest that the friction coefficients of vulcanized rubbers can be reduced by the simple surface microstructures that are applicable to a wide range of fields.