Plasma functionalization of carbon nanotubes and radical penetration mechanism

Owing to their superior properties, carbon nanotubes (CNTs) have attracted significant attention for various applications; however, their aggregation due to van der Waals forces hinders the industrial applications of CNTs. To overcome this problem, previous studies have proposed plasma functionalization, but its analysis is limited to the surface of thin-film materials or involved small quantities of CNTs. In plasma functionalization, radicals need to penetrate from plasma into the CNTs to functionalize the entire CNTs. The radical penetration at all depths of CNTs is experimentally confirmed. The radical penetration mechanism with respect to thickness and free volume between CNTs is modeled using radical diffusion motion with the adoption of Knudsen diffusion.