The effect of pre-treatment methods on morphology and size distribution of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) are important materials with a unique combination of mechanical, electrical and thermal properties. MWCNTs usually exist as tangled aggregates embedding impurities such as catalysts or amorphous carbon. Therefore, purification and cutting process are essential processes to get the well-dispersed solutions in solvents or a polymer matrix for diverse practical applications. In this study, we used MWCNTs with high purity (> 95%) and focused on the cutting effects on the size distribution of MWCNTs. Their size distribution after the cutting process is expected to be a very important factor in determining the final properties of the polymer-MWCNT composite. Gel permeation chromatography (GPC) was effectively demonstrated in analyzing the effect of treatment methods on a size distribution of pre-treated MWCNTs in organic solvent. MWCNT was treated by two different methods. One is an oxidation process with H2SO4/HNO3 solution and the other is an ultrasonic process with high power. MWCNTs were shortened simply by applying high power ultrasonication with narrow length distribution. Meanwhile, the acid-treated MWCNTs became much broader in their sizes and more flexible in their rigidities. These differences led to a different behavior in electric conductivity. These studies promise to optimize pre-treatment processes for tailoring suitable MWCNTs towards future applications.