EFFECTS OF NITRIC-SULFURIC ACID MIXTURE RATIO AND SONICATION TIME ON COVALENT FUNCTIONALIZATION OF HELICAL CARBON NANOTUBES FOR NANOCOMPOSITE APPLICATIONS

摘要

Helical carbon nanotube (HCNT) is one of the configurations of carbon nanotubes (CNTs) that has a great potential for number of high-performance materials applications, because of its particular spiral coil-shaped structure. The coil-shaped geometry increases the mechanical entanglement of these nanotubes with a host resin system, when they are used as reinforcements. This consequently has the potential to improve the mechanical, thermal, electrical, and magnetic properties of the polymeric matrix systems. A uniform dispersion of CNTs in the resin plays an important role in obtaining improved and consistent properties in the final nanocomposite part. To improve the homogeneous dispersion (individual suspension) of these nanotubes in the host resin and to enhance their interactions/bonds with the resin molecules, the surface of these nanotubes should be modified. This study investigates a sonication method for chemical functionalization of HCNTs using a mixture of sulfuric and nitric acids and it evaluates the effects of acidic mixture ratio and the processing time on the severity of functionalization process. The functionalized HCNTs were characterized by SEM, FTIR, XRD, visual dispersion inspection, and Raman spectroscopy methods. The results showed that all functionalization processes were successful. The dispersion rate demonstrated to be independent of the ratio of acidic solution. Furthermore, the use of [3:1] mixture ratio of sulfuric to nitric acids led to lower crystallinity for functionalized HCNTs, compared to the ones that were treated with [1:1] mixture ratio. With respect to the duration of sonication process, no changes in the dispersion homogeneity/stability were observed when the sonication time was extended from 3hr to 6hr. However, using the longest time of sonication (9hr) led to a higher precipitation of the treated HCNTs that were suspended in an aqueous solution.