Beyond a Nature-inspired Lotus Surface: Simple Fabrication Approach Part I. Superhydrophobic and Transparent Biomimetic Glass Part II. Superamphiphobic Web of Nanofibers

Abstract

Nowadays, many people have a dream of mimicking the amazing aspects of nature, in particular their functional surfaces. In nature, there are a great many wonderful functional surfaces, such as the lotus leaf for self-cleaning, a morpho-butterfly wing for structural color, a moth eye for antireflection, the back of a stenocara beetle to capture fog, the foot of a gecko for dry adhesion, a strider’s leg for water resistance, or a snake’s skin as a low friction material [1]. Because biological systems change depending on the environment and circumstances, the surfaces which are always exposed to the outside are well developed for their function, especially in an optimized state. The most interesting feature is that the functional surfaces in nature have a hierarchical structure ranging from macrosize to nanosize as well as a chemical composition that facilitates low surface tension to maximize their role. Among the numerous nature surfaces, this paper focuses on the lotus leaf, a well-known example of a superhydrophobic and self-cleaning surface [2-4]. The lotus is a plant that can grow in murky ponds. The lotus leaf is a symbol of purity in the Orient, because their leaves always remain clean and dry. This phenomenon originated from the non-wetting property of the lotus leaf. The lotus leaf has two levels of roughness structures comprised of both micrometer-scale bumps and nanometer-scale hair-like structures on the surface with a composition of wax. The trapped air on the rough surface makes water droplets bead up at a contact angle in the superhydrophobic range of 150o and then rolls off while collecting any compiled dirt due to the very low sliding angle. In order to prove the transfer of this lotus effect to be technically feasible, there have been numerous attempts to synthesize the surface structures on the low surface tension chemical layer. Fabrication methods have been developed to create structures that mimic the superhydrophobic behavior of lotus surfaces, and these are generally categorized into one of two methods: a top-down or a bottom-up method. The top-down processes can structure