Protonated emeraldine

A synthetic protocol for the formation of conducting filaments of polyaniline in the 3 nanometer wide channels of the aluminosilicate MCM-41 was developed (Figure 11).1°° Aniline vapor was allowed to diffuse into the dehydrated channels of the host at room temperature, followed by immersion into an aqueous solution of peroxydisulfate at 273 K. This reaction produced encapsulated polyaniline filaments. Spectroscopic evidence including UV-VIS and infrared data showed that the filaments are in the protonated emeraldine salt form (for example, Raman spectra exhibit modes indicative of the protonated quinone radical cation structure). A single, rather broad (8 G) electron spin resonance line (for an evacuated sample), at g = 2.0032 suggested slightly lower... 

If the fully protonated i.e. =50% protonated emeraldine base should have the above dication i.e. bipolaron constitution as shown in equation 3, it would be diamagnetic. However, extensive magnetic studies,3-13 have shown that it is strongly paramagnetic and that its Pauli (temperature independent) magnetic susceptibility increases linearly with the extent of protonation. These observations and other earlier studies,show that the... 

From the date recorded on oligomers, we have also studied in details the protonated emeraldine form of the polyaniline and have clarified the delocalization of the charged defects along the chain as a function of the solution acidity. 

In this paper, we have investigated the electronic structure of different base forms of polyaniline by using X-ray photoelectron spectroscopy. The protonated emeraldine form has been also investigated to determine the charge delocalization along the chain as a function of the pH. 

In a first step, the electronic structure of the polyaniline base form has been followed versus the oxidation state. After that, we have proceeded further with the protonated emeraldine form. In all cases, the binding energy scale has been calibrated by setting the Cls core level main peak at 284.4 eV. 

In a second part, the electronic structure of the protonated emeraldine form of polyaniline have been analysed and in particular theNls core level. 

From the study of the short oligomers (dimer and tetramer) , we have discovered two types of charged imine nitrogen defects one localized on the imine nitrogen atoms and one delocalized on two monomer units. They are respectively at + 2.0 0.1 eV and + 1.1 0.1 eV BE towards the neutral amine peak. In this work, we apply these results to the various protonated emeraldine. 

Fig. 4. Evolution of the XPS Nls core level spectra of the protonated emeraldine as a function of the pH solution.

Fig. 2. Optical absorption spectra of films of the fully protonated emeraldine salt l1S] (A )n, spin-cast from sulfuric acid the absorption coefficient is plotted as a function of photon energy. The three spectra were obtained from films with different molecular weights, as inferred from viscosity measurements (see text).

The available data provide the basis for an understanding of the electronic structure of the four principal forms of polyaniline the fully reduced leucoemeraldine, (lA)n the emeraldine base, [(lA)(2A)]n the oxidized and fully protonated emeraldine salt, [lS] (A )n and the fully oxidized bipolaron lattice, (-B-NH+=Q=NH+-)n. 

From the data of Figures 1 and 2, we conclude that the absorption spectrum of partially crystalline films of the high molecular weight and fully protonated emeraldine salt, i.e. [IS] (A )n, bas three important spectral features ... 

Fig. 5 Scheme of redox transformations and protonation equilibria of polyaniline where L, E, P, LHgx, EHgx represent different oxidation and protonation states. E - leucoemeraldine, E - emeraldine, P - pernigraniline, LHgx - protonated leucoemeraldine, EHgx - protonated emeraldine forms. 

Polyaniline (protonated emeraldine), X = 0.5 Chemical synthesis Fibrillar 0.5 55... 

The band structure of fully protonated emeraldine salt was studied previously by semiempirical molecular orbital (MO) calculations and more recently by ab initio calculation [41,42]. A half-filled polaron band formed via the interaction between separate polarons (there are two polarons per tetrameric repeating unit) was proposed to explain the observed optical and electrical properties of fully protonated PANI-ES. The PANI-HCSA films used in these studies were, however, cast from NMP solutions in the form of EB and then doped into the form of ES. The polymer chains in these polymer films, therefore, have the same conformational structure. 

They observed that protonated emeraldine using these dopants has a good solubility in cresol, which is a excellent solvent for many classical polymers such as poly(methyl methacrylate). This methodology of using a dopant having a surfactant group led to the preparation of polyblends with following polymers. Nylon, polycarbonate, polystyrene, polysultone, poly(-vinylacetate) polypropylene, poly(vinylchloride), acrylonitrile butadiene-styrene copolymer (ABS) and poly methyl (methacrylate). 

The intermediate oxidation state has relatively complicated spectra, dependent upon the pH and dominated by the presence of charge carriers (polarons) in the polymer. Two forms of the polymer exist in this state, each having a proposed 3 1 benzenoid quinoid conqx)sition, the emeraldine base ( B) and the protonated emeraldine salt (ES). The visible spectra of the EB form closely matches that of the pemigraniline form since friey both contain similar functional units, the only difference observed in the band at 2.2 eV, which is red shifted to 2.0 eV (620 nm) (18). This red shift accounts for the blue color of this form. The ES form has somewhat more conq>licated spectra, which is a direct ramification of the presence of polarons in the polymer since the population of polaronic sites is dependent upon the concentration of acid in the solution. Generally, though the ES form possesses the following uv-vis bands, 1.5 (830 nm), 2.75-3.1 (450 nm), and 1.0 (1240 nm). The band at 1.0 eV is assigned to an intrachain free-carrier excitation, vdiile the variable band at 2.75-3.1 eV is due to polaron band and the band at 1.5 eV is the excitonic transition observed for EB (17,19). 

Although the protonated emeraldine salt is known to exhibit many properties characteristic of the metallic state [1185, 1192], initial studies yielded transport properties that are not typical of those of a metal [1184-1186]. Instead, the conductivity was found to be activated, and the thermoelectric power showed a complex temperature dependence [1205]. These nonmetallic transport properties arise from a combination of a mesoscopic and molecular-scale disorder generated during synthesis and doping of the material. 

Table 18.1 Solubility and Conductivity of Protonated Emeraldine Salt with (SO3 —R) Counterion...

Figure 11.5 Synthesis of polyaniline (protonated emeraldine form).

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