Synthesis and characterization of polyaniline derivatives and related carbon nanotubes nanocomposites - Study of optical properties and band gap calculation

Poly(o-methylaniline) (POTO), poly(o-methoxyaniline) (POAS), poly(2,5-dimethylaniline) (PDMA), poly(2,5-dimethoxyaniline) (PDOA), and nanocomposite based on multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) embedded in these conducting polymers, were synthesized by oxidative polymerization. We used the Langmuir-Schaefer (LS) technique to fabricate films at the air-water interface and performed the doping process on the undoped films by dipping the substrates in 1 M hydrochloric acid (HCl) aqueous solution. We recorded UV-vis spectra for both the undoped and doped forms and calculated the related band gaps by using the Tauc equation. Experimental data showed the substituents affected the final oxidation ratio of the polymer chains and the presence of carbon nanotubes (CNTs) in the medium of reaction changed the properties in relation of the kind and number of substituents along the aromatic ring. The study of UV-vis spectra of the undoped nanocomposites and the calculated band gaps highlighted that the conducting polymer chains simply wrapped up around CNTs with no strong interaction. Both the kind and number of substituents along the aromatic rings strongly affected the protonation process, since their capability of “tuning” the formation of the polaronic state. The presence of CNTs in the polymer matrix showed no appreciable influence in the chemical properties of the doped nanocomposites with respect to the pure conducting polymers.