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 300-1500 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 micro-structuring of the particle arrays.