Surface effects and wettability measurement considerations in fluorinated carbon nanotubes

With the growing demand of incorporating inherently hydrophobic carbon-based materials including carbon nanotubes (CNTs) with the surrounding medium (air, water, biofluids, etc.), it is inevitable to modify their surface chemistry and wettability with functionalization. Sidewall fluorination of the CNTs has attracted a lot of interest for its effectiveness in surface modification and switching surface wettability. Along with characterization techniques such as Raman and FESEM performed on the as-grown fluorinated CNTs surfaces, surface free energies were calculated based on the contact angle results. Detecting the proficiency of the fluorination treatments on wettability requires reliable water contact angle measurements on non-ideal solid surfaces where local energy minima are separated by energy barriers and the deposited static drop can be in any free energy minimum. Advancing contact angle (ACA) and receding contact angle (RCA) methods were applied to the fluorinated CNTs as well as static contact angle measurements. The former with higher reliability, to date, have not been used on nanotube-covered surfaces. Both methods confirmed the efficiency of tuning wettability of CNTs surfaces with fluorination while ACA–RCA method presented benefits on understanding the surface properties over the static contact angle measurements.