Flame synthesis of amorphous carbon nanobeads and their hydrophobicity

Flame synthesis has been recognized as a desirable cost-effective process for the bulk synthesis of carbon nanostructures like nanotubes and nanofibers. Nanostructured carbon materials, such as carbon nanotubes and nanofibers, also exhibit superhydrophobic behavior over a range of pH values, including for corrosive liquids. This paper describes a rapid on-demand process for the synthesis of remarkably superhydrophobic surfaces on silicon (Si) surfaces using an ethylene-air nonpremixed flame. These amorphous carbon nanobeads exhibit close structural similarity to graphitic nanopearls reported by Levesque, Mouton and their coworkers. We have used 450 μm thick Si wafers as substrates that were inserted into the flame at a 10 mm height above the burner surface for 2.5, 5 and 10 min durations. The resulting flat flame is used as the source of carbon for the growth of these pearl-like structures. One side of the wafers was a polished surface while the other was lapped and etched. Regardless of the side facing the flame, the synthesized nanostructures on them were identical. Crystalline silicon is a widely employed substrate for surfaces with controlled chemical and physical properties (e.g., for biosensors, and for studying biomolecular interactions at interfaces).