Fabrication of Rose Petal Surface Using Release-Coated UV-Curable Resin via Ultraviolet Nanoimprint Lithography

Abstract

Organisms often have superior abilities. For example, the moth’s eyes block the reflection of light, preventing even the slightest light from escaping. Morpho butterflies have vivid colors despite their lack of pigmentation. The superhydrophobicity of lotus leaves is another example, which is attributed to their characteristic surface structure. We have recreated an interesting property by mimicking the structure of rose petals. When a drop of water falls on a rose petal, it adheres to the petal like a sphere. The droplets stay in place when the petals are inverted in this state. This phenomenon is called the rose petal effect. The surface of the petals is lined with microscale hemispherical structures, and each surface has additional nanoscale grooves. The effect is due to the hierarchical structure of nano- and microstructures. When water is dropped onto these structures, the surfaces of the nanostructures become air pockets, preventing water from entering the grooves. This results in stronger water repellency compared to that of the same material with a smooth surface. In contrast, when water penetrates the microstructure, the surface area becomes larger than that of a smooth surface, increasing adhesion. This is called the Wenzel mode. Here, we attempted to reproduce this structure on film using a combination of high-throughput techniques; ultraviolet nanoimprint lithography (UV-NIL) and roll pressing. The manufacturing process comprises two main steps. First, a nanopillar structure called a moth-eye structure is fabricated over the entire surface using UV-NIL. This serves the same purpose as the nanoglobe structure. Next, microscale holes are drilled on the surface using a roll press method. The resulting depressions immobilize water droplets and improve adhesion. Despite the strong water repellency obtained through this method, with a contact angle of more than 140±b°, up to 9 µL of water droplets remained attached to the film even when the film was turned over. Because this method can impart adhesion at any position on the water-repellent surface, it can be applied to microdroplet transport.