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 . 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 . 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).