Complete synthesis of germanium nanocrystal encrusted carbon colloids in supercritical CO2 and their superhydrophobic properties.

Colloidal carbon spheres were synthesized by the carbonization of squalane, a nonvolatile hydrocarbon solvent, in supercritical carbon dioxide. Precise pressure modulation of the fluid medium led to size controlled growth of carbon spheres ranging from 300 to 1500 nm in diameter. This unique synthetic approach of carbonizing a hydrocarbon suspension in supercritical fluid is found to suppress any particle aggregation, resulting in excellent sphere monodispersity. Core-shell hybrid structures of C-Ge were subsequently formed by inducing the growth of 10-40 nm sized germanium nanocrystals from the spheres in a hierarchical bottom-up approach. Extensive characterization of the spheres and nanocrystals was conducted using transmission and scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman, and thermogravametric analysis. Assemblies of nanocrystal modified carbon colloids impart outstanding superhydrophobic properties due to the combined nano- and microstructuring of the particle arrays.