Static Friction of Biomimetic Surface Microstructure of PDMS under Wet and Dry Conditions

摘要

Smooth adhesive pad found among arthropods, amphibians, particularly tree frogs, are usually covered with surface microstructure of different shape to enhance the attachment abilities on the smooth substrate. During the last decade, it has gained more attentions in the development of anti-slippery systems by mimicking these unique characteristics. In this paper, we studied a new amphibian species newt by observing their climbing abilities on wet and dry vertical smooth surface, and found that the newts can even hang on the surface with an inclination angle more than 90~° without falling. We investigated the toe pad micro-structured surface of the newt by using scanning electron microscopy (SEM), and found that an array of hexagonal cells with micro-ridges on cell borders exists for the larvae; while an array of hexagonal cells separated by microgrooves is for the adult. Inspired by these features, the biomimetic micro-structured surfaces were fabricated using a soft elastomeric material polydimethysiloxane (PDMS). Four different micro structures were chosen to study their tribological properties with a solid substrate under wet and dry conditions. The patterns of the microstructures include round pillar, hexagonal pillar, round pillars surrounded by a closed hexagonal ridge, and round pillars surrounded by a semi-closed hexagonal ridge. The static friction tests were carried out using the multi-functional surface meter TYPE12. The results showed that the area ratio of the micro pillar plays a major role in enhancing the static friction for both wet and dry conditions, while the numerical density of the micro pillar has less effect on the friction enhancement. Among the four kind specimens, the specimen with hexagonal pillars would increase the static friction more than others at the same test conditions when the pillar area ratio is lower than 40%.