Sidewall hydrogenation impact on the structure and wettability of spaghetti MWCNTs

Carbonaceous and hydrophobic surfaces of carbon nanotubes require modification by functionalization to interact more efficiently with the surrounding medium such as air, water and bio-fluids. Two types of spaghetti MWCNTs, a less studied category of nanotubes, with the advantage of simpler incorporation with other materials, were fabricated, characterized and hydrogenated. The structural differences of the spaghetti types, mainly due to the structural differences of the substrates they were grown on, were reflected in FESEM and TEM images, XRD patterns and Raman spectra of the two samples. More interestingly, water contact angle measurements on initial hydrophobic structures showed a distinct wettability behavior in the two types with hydrogenation time, where one became even more hydrophobic and the other switched to hydrophilic. The inherent structural differences between the two types, the surface roughness, the increase in the hydrogen content on the sidewalls of the nanotubes and the interplay of repulsive Columbic and attractive van der Waals forces among the hydrogens and the nanotubes may have all played a role in this wettability behavior. However, the capability of switching surface wettability on demand is very useful for future environmental applications and may support unique devices in microfluidics, catalysis, and detection systems. Graphic abstract