Protonation, sol formation and precipitation of poly‐ and oligoanilines

Abstract

Raman spectrometry, UV-visible-near IR and attenuated total reflection IR absorptions are used to analyze the protonation of the emeraldine form of the phenyl/ -NH 2 end-capped BQBBa tetramer and of the phenyl/ -NH 2 end-capped (BQBB) 4 a hexadecamere in strong (H 2 SO 4 or HCl), intermediate (CH 3 COOH) and weak (CH 3 OH) acids. Evolution of the pristine solution with aqueous dilution and time is analyzed in order to understand the formation of a sol of nanofilaments, which agglomerate and finally precipitate. Water in an acidic solution favors the precipitation of the corresponding emeraldine salt material, i.e. increases the degree of aggregation of the oligomeric species and the aromatic behavior of the rings. The secondary doping effect consists in intercalation of water molecules in the highly aggregated (paramagnetic) species, strongly bound to the oligomeric units and whose removal is always accompanied by elimination of the protonating agent (primary doping). The role of interchain interactions in charge carrier mobility appears more important than that of intrachain behavior.

Characterization of the products of aniline peroxydisulfate oligo/polymerization in media with different pH by resonance Raman spectroscopy at 413.1 and 1064 nm excitation wavelengths

“…2 is very similar to that of PANI–ES. The assignment of the bands can be found in the literature 5–7, 31–33. The spectra of the products formed in the reactions at initial pH values of 5.3–13.2 are very similar.…”

“…Although the intense electronic absorption band at 370 nm could be assigned to π–π* transitions, spectral features of these samples are very different from those of PANI–ES. Additionally, the spectrum of P13.2 sample also differs from the PANI–EB spectrum, which presents bands at 330 and 630 nm 5–7, 31–34. All these observations indicate that P5.3–P13.2 samples are different from the standard oligomers of PANI.…”

“…Generally, the polymeric material formed in the conventional synthesis has no well‐defined morphology or shape in the nanometer scale 1, 3, 4. The electronic, vibrational and electron paramagnetic resonance spectra of standard PANI oligomers formed by the head‐to‐tail units of monomers having different degrees of oxidation have been well studied 5–7. Through these works, it was possible to understand the behavior of charge carrier units and the strategies to enhance PANI–ES conductivity.…”

The First Stages of Chemical and Electrochemical Aniline Oxidation—Spectroscopic Comparative Study

“…Significant differences are observed between UV-Vis absorption spectra obtained on glass substrates removed from the reaction mixtures at pH 1 and 7 at various times (Figure 4). Whereas in the strongly acidic medium, PANI in the emeraldine (15 min, final) [41,[50][51][52][53] and pernigraniline (2 min, 10 min) [48,52] salt form is observed. The evolution of the UV-Visible absorption spectra of the product formed at pH 7 are more complex.…”

The interaction of thin polyaniline films with various H‐phosphonates: Spectroscopy and quantum chemical calculations

“…The band at 320 nm is connected with π–π* transitions in benzenoid units (B‐band) and the band at 600 nm with exciton‐like transitions in quinone diimino units (Q‐band). In the spectrum of PANI‐S (Figure ), the B‐band is red‐shifted to about 330 nm, the Q‐band is missing, and the bands located approximately at 430 and 850 nm are attributed to polaronic transitions …”