Raman spectroscopic studies on the structural changes of electrosynthesized polypyrrole films during heating and cooling processes

Abstract

Polypyrrole films were electrochemically synthesized by direct oxidative polymerization of pyrrole in acetonitrile containing ␤-naphthalene sulfonic acid or tetrabutylammonium tetrafluoroborate as an supporting electrolyte. We characterized the as-grown polypyrrole films by resonance Raman spectroscopy in the temperature region of Ϫ195 to 275°C. During the heating process, the Raman bands related to the oxidized species decreased gradually, due mainly to the affect of oxygen and moisture in the air, and, finally, the neutral polymer chains decomposed into disordered carbons. During the cooling process, polymer chains changed from disordered (coil-like) to ordered (rodlike) structures and caused the elongation of the conjugated chain length. This results in a red shift of the absorption of the electron spectra of the polymer and the enhancements of the Raman bands related to the oxidized species.

Hysteresis Phenomenon in Heat–Voltage Curves of Polypyrrole-Coated Electrospun Nanofibrous and Regular Fibrous Mats

“…This possibly results in reorientation of the molecular chains 32 as well as reconfiguration of the conjugation system in the PPy structure, 33 and thereby a large number of electrons can flow through the PPycoated fibrous mats. 34 This is further confirmed by the fact that the efficiency of charge transfer as well as the electron delocalization between the PPy chain and the dopant anion increases at higher voltages. 35,36 From the above discussion, it can be assumed that, once the voltage decreases from 35 V to 25 V in the return path, the conjugation length of the PPy chain elongates.…”

Polypyrrole/TiO2 nanotube arrays with coaxial heterogeneous structure as sulfur hosts for lithium sulfur batteries

“…The band at around 1080 cm -1 is assigned to C-H in-plane deformation [37]. The double peaks at about 990 cm -1 and 940 cm -1 are respectively assigned to the ring deformation associated with radical cation (polaron) and dication (bipolaron) [38]. S/PPy/TiO2 NTs-160 and S/PPy/TiO2 NTs-300 still show the three main peaks of elemental sulfur but with very low intensity, which means sulfur is well confined in the nanotube arrays.…”

Electrochemical actuator based on single-layer polypyrrole film

“…The strong band located at approximately 1580 cm −1 represents the C C backbone stretching of PPy. The double peaks at about 1050 and 1080 cm −1 are assigned to the C H in plane deformation [24]. The other double peaks at approximately 1320 and 1370 cm −1 are attributed to the ring-stretching mode of PPy [25].…”