Comparison of branched and linear perfluoropolyether chains functionalization on hydrophobic, morphological and conductive properties of multi-walled carbon nanotubes

Abstract

The functionalization of multi-walled carbon nanotubes (MW-CNTs) was obtained by generating reactive perfluoropolyether (PFPE) radicals that can covalently bond to MW-CNTs’ surface. Branched and linear PFPE peroxides with equivalent molecular weights of 1275 and 1200 amu, respectively, have been thermally decomposed for the production of PFPE radicals. The functionalization with PFPE chains has changed the wettability of MW-CNTs, which switched their behavior from hydrophilic to super-hydrophobic. The low surface energy properties of PFPEs have been transferred to MW-CNTs surface and branched units with trifluoromethyl groups, CF3, have conferred higher hydrophobicity than linear units. Porosimetry discriminated the effects of PFPE functionalization on meso-porosity and macro-porosity. It has been observed that reactive sites located in MW-CNTs mesopores have been intensively functionalized by branched PFPE peroxide due to its low average molecular weight. Conductivity measurements at different applied pressures have showed that the covalent linkage of PFPE chains, branched as well as linear, weakly modified the electrical conductivity of MW-CNTs. The decomposed portions of PFPE residues, the PFPE chains bonded on carbon nanotubes, and the PFPE fluids obtained by homo-coupling side-reactions were evaluated by mass balances. PFPE-modified MW-CNTs have been characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), static contact angle (SCA), surface area, and porosity measurements.