Surface and structure modification of carbon nanofibers

The micro-structure of reinforcements, including surface characteristics, plays a critical role in the properties of composite materials that are ultimately produced. The purpose of this work is to investigate the micro-structure of carbon nanofibers (CNFs) with different core structures, which are hollow (PR) and solid (MJ) fibers, as a function of two treatments: CVD and thermal. From Raman spectroscopy and XRD analyses, an increase of crystallite thickness and width was observed after a heat treatment at 2200 °C for both types of fibers. Further, there was a more significant enhancement of crystalline structure in PR fibers. Also, an increase in thermal oxidation stability for heat-treated CNFs was observed. BET adsorption isotherms showed a significant reduction of specific surface area of MJ fibers after the heat treatment and also after the CVD surface treatment, resulting from the decrease of pore volume. However, even after heat treatment, MJ fibers possessed rougher surface than did PR fibers. Further, significant spatial discontinuity was observed with TEM micrographs due to reorganization of graphene layers during heat treatment for the both heat-treated CNFs. These results suggest that surface and structure of CNFs are important for maximizing their role in the performances of nanocomposites.