Optimizing the degree of carbon nanotube dispersion in a solvent for producing reinforced epoxy matrices

• Highly dispersed untreated CNT was achieved at input sonication energy of 85,785 J.
• The CNT diameter exhibited a significant influence on the CNT dispersion.
• The CNT length does not affect the dispersion of CNTs.
• Higher steric repulsion of copolymers led to higher level CNT dispersion.
• BYK copolymers with higher surface charge yield more dispersed CNTs.

The homogeneous incorporation of a small concentration of carbon nanotubes (CNTs) in epoxy matrices can enhance the mechanical properties of the composites. However, due to the high van der Waals interaction energy between CNTs, it is difficult to achieve a homogeneous dispersion of them in the epoxy matrix. Both processing conditions of the nanotubes, as well as the addition of surfactants have the potential to improve the dispersion. In this paper, the effects of sonication energy, CNT geometry and dispersant type on the dispersion degree of CNTs and consequent reinforcement of the epoxy matrix are investigated. Multi-walled CNTs with variable diameter and length were dispersed in ethanol using different sonication energies, with the aid of different dispersants. The results show that an increase in sonication energy initially leads to more CNT dispersion, although after a certain value of sonication energy, the level of dispersion remains constant. Moreover, excessive sonication energy was found to shorten the length of CNTs and thus decrease their aspect ratio. Due to the lower interaction energy of CNTs with larger (40–60 nm) diameter, compared to those with smaller diameter (10–20 nm), the larger diameter nanotubes showed a great ability to be dispersed, while CNT length showed no significant effect on the degree of dispersion. For greater CNT dispersion additives were incorporated. Copolymers which were able to disperse the CNTs primarily by steric repulsion were found to be more influential than those which dispersed the CNTs mainly by electrostatic repulsion, such as oleic acid. Furthermore, it was also found that copolymers yielding greater surface charge on the CNT were able to disperse CNTs more than those copolymers leading to a lower surface charge. It was found that, the incorporation of 0.1 wt.% pristine CNT using optimized influential parameters resulted in high levels of homogeneous dispersion in the epoxy matrix, with a modest improvement in mechanical properties of epoxy. This study provides further insight into the dispersion of CNTs in composite matrix and the degree to which a controlled dispersion can allow the CNTs to reach their potential as reinforcing nanofillers.

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