Fabricating Bio-inspired Micro/Nano-Scale Surfaces For Anisotropic Properties

Specific micro/nano-scale structure endows special properties to biological surfaces in nature, for example, self-cleaning phenomenon, superhydrophobic surfaces, anisotropic water transportation, anti-reflection, anisotropic adhesion, etc. All those special properties are closely related to materials properties and microstructures.We hydrophobic treated hydrophilic silica nanospheres with amphiphilic CTAB, and self-assembled silica nanospheres via water/air interface self-assembly into large are monolayer on polymer substrate. Through two steps Reactive Ionic Etching (RIE), we first etched close-packed nanosphere arrays into non-close-packed ones. Next, we utilized smaller silica nanospheres as mask, etched polymer substrate, which led to inclined polymer nanopillar arrays.We first examined the anisotropic properties related to wetting phenomena. It was found that static contact angle was different between the directions along the patterned strip microstructure and perpendicular to it. It was also found that dynamic contact angle (sliding angle) was different between the directions along the RIE etching and against it. Moreover, we found that by increasing polymer RIE treatment time, we obtained nanopillar arrays with higher aspect ratio, as long as smaller dynamic contact angle. This finding illustrated that the adhesion to water of the fabricated surfaces could be controlled by RIE treatment parameters. Such surfaces with controllable adhesion to water had potential in microfluid fields.Secondly, we also study the anisotropic solid-solid interface adhesion properties of the polymer nanopillar arrays. As for dry polymer adhesives, polymer elastic modulus, pillar aspect ratio, and inclined angle are three most important parameters which impact adhesion behavior. We modulated these three parameters, and prepared a series of polymer nanopillar arrays. After micro-scale adhesion test, it was found that the prepared microstructures had anisotropic adhesion properties to some extent. Such surfaces with anisotropic adhesion had potential in climbing robots, biomedical applications, etc.