Covalent functionalization of carbon nanotubes for ultimate interfacial adhesion to liquid crystalline polymer

In this study, we have selectively introduced three types of chemical functional groups, namely nitrophenyl (C6H4NO2), aminophenyl (C6H4NH2) and benzoic acid (C6H4COOH), on the sidewalls of multiwalled carbon nanotubes (MWCNTs) with the aim to find the optimal functionalization of MWCNTs for the most desirable intermolecular interaction with a liquid crystalline polymer (LCP). We have investigated the effects of electron withdrawing (-NO2 and -COOH) and donating (-NH2) groups attached to the benzene rings of the functionalized MWCNTs on the dispersion of MWCNTs in the LCP matrix and the interaction with the LCP. FTIR analysis showed that the composite containing -C6H4NH2 functionalized MWCNTs exhibited the maximum intermolecular interactions (hydrogen bonding) between the -C6H4NH2 group of MWCNTs and -C[double bond, length as m-dash]O group of LCP. This strong intermolecular hydrogen bonding greatly improved the dispersion of p-C6H4NH2 functionalized MWCNTs in the polymer matrix as well as the interfacial adhesion. The highest complex viscosity, storage modulus and loss modulus were observed for the p-C6H4NH2-functionalized MWCNT/LCP composites among all the composites studied. The mechanical strength and electrical conductivity of this composite system were also the highest. Thus, these results testified that the extent of intermolecular interactions between the functionalized MWCNTs and the polymer matrix is key for an optimal improvement in the composite properties.