Plasma functionalization of carbon nanotubes and radical penetration mechanism

Abstract

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.

Enhanced Hydro-Actuation and Capacitance of Electrochemically Inner-Bundle-Activated Carbon Nanotube Yarns

“…7,13,14 Although CNTs in the outer layer are functionalized by a direct reaction with the highly energetic species, the shadowing of outermost CNT layers and the short penetration depth of plasma does not allow the active species to penetrate inside. 15 Moreover, the extremely short lifetimes of the species (less than 1 ms) also hinder them to reach the internal area. 15,16 Consequently, in most cases, oxygen plasma penetrates only up to a few micrometers from the surface.…”

“…15 Moreover, the extremely short lifetimes of the species (less than 1 ms) also hinder them to reach the internal area. 15,16 Consequently, in most cases, oxygen plasma penetrates only up to a few micrometers from the surface. Thus, the development of holistically and homogeneously activated CNTs by plasma treatments has rarely been reported to date.…”

“…Thus, the development of holistically and homogeneously activated CNTs by plasma treatments has rarely been reported to date. 14,15 Although plasma treatment is obviously an excellent CNT activation method, it is undesirable for onedimensional and nano-bundle-braided CNT yarns, which have limited microscale sizes, surface areas, and volumes. In other oxidizing methods, such as acid treatments or air oxidation (including thermal, photonic, and gas treatment) using a fluidtype oxidant, the reactants can infiltrate the interbundle gaps.…”

“…Ham et al fabricated plasma-treated multiwalled CNT (MWNT)-based gas, humidity, and immuno-sensors; He et al fabricated a water-responsive actuator and implantable supercapacitors with plasma-treated CNT yarns , Shao et al and Adusei et al reported yarn-based supercapacitors with increased electrochemical capacitances using oxygen plasma treatment. , However, despite several advantages, plasma treatment has an inherent limitation for CNT activation. The effects of plasma are limited to the superficial CNT layers, leaving the inner region unfunctionalized. ,, Although CNTs in the outer layer are functionalized by a direct reaction with the highly energetic species, the shadowing of outermost CNT layers and the short penetration depth of plasma does not allow the active species to penetrate inside . Moreover, the extremely short lifetimes of the species (less than 1 ms) also hinder them to reach the internal area. , Consequently, in most cases, oxygen plasma penetrates only up to a few micrometers from the surface.…”

“…The effects of plasma are limited to the superficial CNT layers, leaving the inner region unfunctionalized. ,, Although CNTs in the outer layer are functionalized by a direct reaction with the highly energetic species, the shadowing of outermost CNT layers and the short penetration depth of plasma does not allow the active species to penetrate inside . Moreover, the extremely short lifetimes of the species (less than 1 ms) also hinder them to reach the internal area. , Consequently, in most cases, oxygen plasma penetrates only up to a few micrometers from the surface. Thus, the development of holistically and homogeneously activated CNTs by plasma treatments has rarely been reported to date. , Although plasma treatment is obviously an excellent CNT activation method, it is undesirable for one-dimensional and nano-bundle-braided CNT yarns, which have limited microscale sizes, surface areas, and volumes.…”