Up to now, most of the research on superhydrophobic surface focus

Up to now, most of the research on superhydrophobic surface focused on Ralimetinib in vitro measuring the CAs and sliding angles (SAs) of water droplets with a volume not smaller than 2 μL (approximately 1.6 mm in diameter). However, we often observe water droplets with a volume lower than 2 μL, such as fog droplets, existing or

sliding on a solid surface in nature. There is a need to reveal the interfacial interaction between superhydrophobic surface and tiny water droplets. Generally, pristine carbon nanotubes (CNTs) are hydrophobic materials, which have also been used to H 89 cell line construct a superhydrophobic surface [15, 16]. By making micropatterns, the hydrophobicity of a CNT surface is further enhanced. The CA between water and CNT pattern is usually larger than 150°, but the SA is

also large (usually larger than 30°) [17, 18]. However, the superhydrophobic CNT forest might also selleck absorb water, resulting in collapsing into cellular foams when water evaporates from interstices of nanotubes [19]. After wetting, the CNT forest might lose its superhydrophobic properties. It needs to construct a stable and durable superhydrophobic surface even wetted by vapor or tiny water droplets. Here, we fabricate the superhydrophobic hierarchical architecture of CNTs on Si micropillar array (CNTs/Si-μp) with large CA and ultralow SA. The CNTs/Si-μp show a durable superhydrophobic surface even after wetting using tiny water droplets. Methods Si micropillar (Si-μp) arrays with defined squares (see Figure  1a, inset) were etched

from a Si (100) wafer by ultraviolet lithography (UVL) and deep reactive-ion etching (DRIE) in sulfur hexafluoride (SF6) and perfluoro-2-butene (C4F8). The height of the Si-μp was controlled by etching time. A standard cleaning process developed by the company Radio Corporation of America (RCA) was carried out to eliminate residual metal and organic species followed by removing Si oxide in a buffered HF solution. The Si micropillar arrays and planar Si wafer were coated with a thin layer of aluminum (10 nm) using an e-beam evaporator for CNT growth. CNTs were grown by floating chemical vapor deposition method, using xylene as carbon source, Oxymatrine ferrocene as catalyst precursor, and a mixture of Ar and H2 as carrier gas, according to our previous report [20]. During the growth of CNTs, the ferrocene/xylene solution (20 mg/mL) was fed into the reactor at a rate of 0.2 mL/min, and Ar and H2 were fed at 400 and 50 sccm, respectively. Figure 1 SEM characterization of various samples. (a) Si micropillar array. (b) Hierarchical architecture of CNTs/Si-μp. (c) Connection between a Si micropillar and CNT forests. (d) CNT forest growing on a planar Si wafer. The samples were characterized using a scanning electron microscope (SEM). The CA and SA were measured using a contact angle goniometer (Rame-hart 300, Rame-hart Instrument Co., Succasunna, NJ, USA).

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