Raman spectroscopic evidence for interfacial interactions in poly(bithiophene)/ single-walled carbon nanotube composites
M. Baibarac, I. Baltog, S. Lefrant
Carbon, Volume 47, Issue 5,April 2009, Pages 1389-1398
Electrochemical polymerization of 2,2′-bithiophene (BTh) on single-walled carbon nanotube (SWCNT) films has been studied by Raman scattering and infrared absorption spectroscopy. Covalent functionalization of SWCNTs with poly(bithiophene) (PBTh) in its un-doped and doped states is demonstrated. The occurrence of a charge transfer process at the interface of PBTh and SWCNTs, is shown by: (i) an up-shift of the Raman lines associated with the radial breathing modes of SWCNTs that reveals both a doping process and an additional twisting together as a rope with the conducting polymer as binding agent; (ii) a new Raman band in the range 1430–1450 cm−1 indicating the functionalization of SWCNTs with PBTh in doped and un-doped states; (iii) strong absorption bands situated in the interval 600–800 cm−1 resulting from steric hindrance produced by the nanotube binding to the polymeric chain. Treatment of the PBTh/SWCNT composite with aqueous NH4OH solution forms un-doped PBTh covalently functionalized SWCNTs. At the resonant excitation of the metallic tubes, an additionally enhanced Raman process is generated by plasmon excitation in the metallic nanotubes. It is evidenced by a particular behavior in the Stokes and anti-Stokes branch of the PBTh Raman line at 1450 cm−1.
Abnormal anti-Stokes Raman emission at electronic resonant excitation (kexc = 676.4 nm) of PBTh deposited by cyclic voltammetry (CV) on an Au rough support. In (a) and (b) are presented the Raman spectra of PBTh film (thin and thick) obtained by achievements of 2 and 10 voltammetric cycles, respectively. The red dashed curves illustrate the anti-Stokes replicas calculated with the Boltzmann formula applied to the Stokes spectra.
Raman and FTIR spectroscopy as valuable tools for the characterization of polymer and carbon nanotubes based composites
S. Lefrant, M. Baibarac and I. Baltog
J. Mater. Chem., 2009, 19, 5690-5704
The combination of the unique properties of carbon nanotubes (CNTs) with conjugated polymers makes their combined composite materials interesting as multifunctional systems with great potential. Supercapacitors, lithium rechargeable batteries, sensors, photovoltaic cells and photodiodes, optical limiting devices, solar cells, high-resolution printable conductors, electromagnetic absorbers and advanced transistors are among the most promising applications. Knowledge of the molecular structure of such compounds is essential for a better use, and for that reason vibrational spectroscopies are fruitful techniques. Therefore, this feature article presents recent progress in the characterization of composites based on conjugated polymers and carbon nanotubes. The contribution of Raman scattering and FTIR spectroscopy to establish the type of interaction between the two constituents will be discussed for different cases, i.e. bi-layers of polymers and carbon nanotubes, doped conjugated polymers with carbon nanotubes and covalently functionalized carbon nanotubes with conjugated polymers. In addition, surface enhanced Raman scattering (SERS) has also proven to be a suitable technique for characterization by providing signal enhancements, allowing for instance the detection of reactions at interfaces or the exploitation of properties associated with nanostructures. As an example, an extra increase of the Raman signal of a polymer deposited on a carbon nanotube thin film demonstrates the generation of surface plasmons in metallic tubes.