Characterization at Atomic Resolution of Carbon Nanotube/Resin Interface in Nanocomposites by Mapping sp²-Bonding States Using Electron Energy-Loss Spectroscopy

Abstract

Functionalization is critical for improving mechanical properties of carbon nanotubes (CNTs)/polymer nanocomposites. A fundamental understanding of the role of the CNT/polymer interface and bonding structure is key to improving functionalization procedures for higher mechanical performance. In this study, we investigated the effects of chemical functionalization on the nanocomposite interface at atomic resolution to provide direct and quantifiable information of the interactions and interface formation between CNT surfaces and adjacent resin molecules. We observed and compared electronic structures and their changes at the interfaces of nonfunctionalized and functionalized CNT/polymer nanocomposite samples via scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) spectrum imaging techniques. The results show that the state of sp2 bonding and its distribution at the CNT/resin interface can be clearly visualized through EELS mapping. We found that the functionalized CNT/polymer samples exhibited a lower fraction of sp2 bonding and a lower π*/σ* ratio compared with the nonfunctionalized cases. A good correlation between near-edge fine structures and low-loss plasmon energies was observed.

Influence of Oxygen-Containing Functional Groups on the Environmental Properties, Transformations, and Toxicity of Carbon Nanotubes

“…This energy loss is greater than or equal to the binding energy of the electrons in the CNT sample that interact with the incident electrons, which results in absorption edges in the EELS spectrum at element-specific energies. The spectral intensity of the oxygen adsorption edge can be compared to that of other elements to determine the atomic percentage of oxygen in a CNT sample, while the near-edge structure of the C K-edge (C 1s) spectra provides information on the local bonding environment (i.e., sp 2 - and sp 3 -hybridized carbon and the ratio of σ* to π* antibonding orbital character) . Similar to EELS, NEXAFS also creates element specific absorption edges, with a near-edge structure that provides information on the local bonding environment.…”

“…The spectral intensity of the oxygen adsorption edge can be compared to that of other elements to determine the atomic percentage of oxygen in a CNT sample, while the near-edge structure of the C K-edge (C 1s) spectra provides information on the local bonding environment (i.e., sp 2 -and sp 3 -hybridized carbon and the ratio of σ* to π* antibonding orbital character). 115 Similar to EELS, NEXAFS also creates element specific absorption edges, with a near-edge structure that provides information on the local bonding environment. NEXAFS requires a tunable Xray source typically provided by a synchrotron, limiting the ease of its routine use.…”

Enhancement of short/medium-range order and thermal conductivity in ultrahard sp3 amorphous carbon by C70 precursor

“…We can see that the 1s-π* peak at 285 eV, corresponding to sp 2 carbon, gradually decreases with increasing P - T conditions, and is finally absent for the AC70-1 sample recovered from 30 GPa and 1100 °C. Using sp 2 glassy carbon as the standard material, the percentage of sp 3 −hybridized carbon is quantified as high as 96.2 ± 0.9% from a calculation of the ratio of integrated areas under the π* and σ* peaks 29 , 38 . The results indicate that C 70 transforms into nearly pure sp 3 amorphous carbon at 30 GPa and 1100 °C.…”

High Interfacial Shear Strain in Polyurea–Carbon Nanotube Composite Sheets

“…43 Polyurea interacts with CNT through π − π, 29 CH−π, 17,29 and NH−π 34,35 noncovalent interactions, as it contains nitrogen as well as aromatic and aliphatic groups (Figure 1f). 44 Studies on the interfacial characterization of polymer−CNT composites have been conducted using Raman spectroscopy, 20 wetting measurements, 45 Fourier transform infrared spectroscopy (FTIR), 17,45 X-ray scattering, 30 electron energy loss spectroscopy (EELS), 46,47 and CNT pullout tests using atomic force microscopy (AFM). 48−51 Theoretical 52,53 and computational models 11,54,55 have been developed and utilized toward this end as well.…”

“…Studies on the interfacial characterization of polymer–CNT composites have been conducted using Raman spectroscopy, wetting measurements, Fourier transform infrared spectroscopy (FTIR), , X-ray scattering, electron energy loss spectroscopy (EELS), , and CNT pullout tests using atomic force microscopy (AFM). − Theoretical , and computational models ,, have been developed and utilized toward this end as well. Raman spectroscopy has proven to be a powerful tool for characterizing the interfacial load transfer. , The tensile strain in CNTs results in a Raman band frequency downshift (D ∼ 1300 cm –1 , G ∼ 1580 –1 , and G′ ∼ 2600 –1 ), which in turn is associated with the weakening of C–C bonds .…”