Functionalization of Multiwalled Carbon Nanotubes with Cyclic Nitrones for Materials and Composites: Addressing the Role of CNT Sidewall Defects

An efficient approach to the organic functionalization of multiwalled carbon nanotubes (MWCNTs) for the production of highly soluble/dispersible materials has been accomplished by a class of highly reactive and thermally stable nitrones. Besides the unprecedented solubility in aprotic polar solvents of the functionalized samples (up to 10 mg of f-MWCNTs per mL of DMF), we have demonstrated, for the first time, that the CNT functionalization by nitrones preferentially occurs at the defective CNT sidewalls without any appreciable degradation of their sp2 network. The role of the reticular imperfections on the graphitic lattice of the MWCNTs has been experimentally and theoretically addressed. A complete chemical (TGA-MS, FT-IR, SSA) and morphological (TEM, AFM) characterization of the functionalized materials has accounted for the high degree of CNT functionalization, whereas Raman scattering, in combination with complementary XRPD and active surface area (ASA) measurements, has provided unambiguous evidence of the key role played by the structural “disorder” of the MWCNTs in the nitrone cycloaddition. Density functional theory (DFT) calculations on the reactivity of selected topological defects at the CNT sidewalls have contributed to trace-out a “defect-based” sidewall reactivity trend. The excellent processability of the functionalized MWCNTs has been finally exploited for the preparation of highly homogeneous CNT/polymer nanocomposites with CNT loadings as high as 3 wt%.