Gradient wettability induced by deterministically patterned nanostructures

Abstract

We report a large-scale surface with continuously varying wettability induced by ordered gradient nanostructures. The gradient pattern is generated from nonuniform interference lithography by utilizing the Gaussian-shaped intensity distribution of two coherent laser beams. We also develop a facile fabrication method to directly transfer a photoresist pattern into an ultraviolet (UV)-cured high-strength replication molding material, which eliminates the need for high-cost reactive ion etching and e-beam evaporation during the mold fabrication process. This facile mold is then used for the reproducible production of surfaces with gradient wettability using thermal-nanoimprint lithography (NIL). In addition, the wetting behavior of water droplets on the surface with the gradient nanostructures and therefore gradient wettability is investigated. A hybrid wetting model is proposed and theoretically captures the contact angle measurement results, shedding light on the wetting behavior of a liquid on structures patterned at the nanoscale. A new method for producing wettability gradientsA new approach developed by researchers in China makes it possible to manufacture materials with continuously varying wettability along their surface. A team led by Wen-Di Li of the University of Hong Kong and Xing Cheng of Southern University of Science and Technology came up with an approach that begins with interference lithography to create a variable intensity pattern with circular symmetry. This created nanostructures in a photoresist, which then served as the base for fabricating a UV-cured mold, which could then be used to transfer the pattern onto a polymer. This approach eliminates the need for costly fabrication processes. The team used this approach to generate a surface with a wettability gradient and investigate its properties, which they found were best described by a hybrid combination of the classic Wenzel and Cassie wetting models.