Raman dispersion in polyaniline nanofibers

In this work the Raman dispersion observed for the polyaniline (PANI) nanofibers was investigated. PANI nanofibers were prepared by interfacial polymerization using HCl or HClO4 acids as dopant. The use of different acids in the aniline polymerization can produce PANI fibers with different diameters. The polymers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), small angle X-ray scattering (SAXS), UV-VIS-NIR and resonance Raman (RR). By using several laser lines (from 1.16 to 3.05 eV) the dependency of νCN band frequencies, related to the quinoid rings, with the laser lines was investigated. The Raman dispersion of νCN frequencies was analyzed using Amplitude Mode Model (AMM). Excitation photon energy versus ∏n(ωnRωn0)2 curves were linear in region of the electronic absorption transition. The Raman dispersion of PANI nanofibers with smaller diameter (d ≈ 30 nm) shows lower dispersion D rate (slope of ∏n(ωnRωn0)2 versus laser line energies) and as consequence higher torsion of Cring-N-Cring segments. Hence, for PANI with higher morphological organization has more stacking between quinoid rings (higher torsion angles) and more electronic homogeneity (lower D rate) compared to other samples.