Certain rose petals are known to be superhydrophobic with high adhesion. There also exist rose petals which are superhydrophobic with low adhesion similar to lotus leaf. The purpose of this study is to characterize systematically the superhydrophobic rose petal with high and low adhesion surfaces and understand the mechanism for adhesion characteristics. Based on these, artificial superhydrophobic surfaces with high and low adhesion are fabricated using a two-step molding process and wax evaporation method. It is shown that the pitch values of microstructures and density of nanostructures play an important role in real rose petals and artificial surfaces to control their adhesion properties.

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The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on alloy steels by both nano-flake or needle patterns and tuning of the surface energy. Steels were provided with hierarchical micro/nanostructures of Fe oxides by fluorination and by a subsequent catalytic reaction of fluorine ions on the steel surfaces in water. A hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective regions surrounded by superhydrophobic surfaces. We show that wettability contrast surfaces align liquid water within patterned hydrophilic regions during the condensation process. Furthermore, this method could have a greater potential to align other liquids or living cells.