Humidity-Modulated Core-Shell Nanopillars for Enhancement of Gecko-Inspired Adhesion

Abstract

The contribution of water to gecko and gecko-inspired adhesion remains a debate. Here, by investigating the adhesion performances of gecko-inspired nanopillar arrays in humid environments, the function of water in dry adhesion is discussed. Adhesion increases with the increase of relative humidity for both hydrophilic and hydrophobic nanopillar arrays. The superficial layer of both kinds of nanopillars are softened by water, forming a kind of ``soft shell-stiff core'' structure. The core-shell structure reduces the stress at contact perimeter, enlarges the cohesive zone, and increases the tolerance to misalignment on contacting surfaces, contributing to the enhancement of normal adhesion. The result suggests a mechanism for the function of water in gecko and gecko-inspired dry adhesions.