A new acid-processing route to polyaniline films which exhibit metallic conductivity and electrical transport strongly dependent upon intrachain molecular dynamics

Abstract

Conductive polyaniline (PANi) films have been prepared via a new route comprising 2-acrylamido-2-methyl-1-propanesulphonic acid (AMPSA) as both the protonating acid and the solvating group, and dichloroacetic acid (DCA) as a solvent. The AMPSA content was varied so that between 30 and 100% of the nitrogen sites on polyaniline could be protonated. The temperature dependence of the conductivity of the films was measured between 15 and 300 K. Above 75-115 K, depending upon the protonation level, a negative temperature coefficient was observed. At 240-260 K a new transition was observed, essentially independent of the protonation level, above which the negative temperature dependency becomes much stronger. The conductivity data were fitted using a simple model employed previously for films of polyaniline camphorsulphonate, and comparisons made between the two systems. Differential scanning calorimetry measurements on a series of films showed an endothermic transition centred at 240-254 K, whose magnitude is dependent upon the AMPSA content. This thermal transition is ascribed to increased motion in the AMPSA anions when heated to above the transition temperature. The AMPSA anion may be considered to behave as a side chain ionically bonded to the PANi backbone, whose particular structure will affect the intrachain molecular dynamics, and hence electrical transport properties of the bulk polymer. The observed thermal transition correlates well with the new transition seen in the conductivity data. It was possible to draw films of uniaxially both at room temperature and at 363 K. The room temperature conductivity along the stretch direction was increased to a maximum value of for a film drawn at 363 K, compared to for an undrawn sample. The films are compared to previous results obtained with polyaniline films protonated with 10-camphorsulphonic acid (CSA).

Doping-dependent studies of the Anderson-Mott localization in polyaniline at the metal-insulator boundary

“…The values are consistent with previous studies. 19,20 Despite the fact that measurements at temperatures below 10 K were unattainable inhibiting a more accurate determination of the resistivity ratio, from the low values of r and the weak temperature dependence of demonstrated in Fig. 2, it can be surmised that all the samples are on the metallic side of the I-M transition.…”

“…͑4͒, with notable accuracy after the application of the LMD model. The values obtained for the free charge carrier concentration (ϳ10 20 cm Ϫ1 ) and the relaxation time (ϭ1/␥ ϳ10 Ϫ15 sec) are characteristic of a dirty metal, 33 implying that the mechanism of transport in conducting polymers, despite their structural difference due to the one-dimensional ͑1D͒ polymer chains, is not fundamentally different from the 3D delocalization that takes place in amorphous metallic bundles. Nevertheless, the subtle details of the transport mechanism such as the relative importance of the interplay between the quasi-1D nature of the system and the 3D features due to contribution from interchain and counterion interactions are yet to be decided.…”

Developments in conducting polymer fibres: from established spinning methods toward advanced applications

“…101 In 1998, a new acid processing route to PAni was reported by Adams et al, using 2-acrylamido-2-methyl-l-propanesulfonic acid (AMPSA) as both protonating acid and solvating group, and dichloroacetic acid (DCA) as solvent. 105 One year later, in what may be considered as a first, PAni fibres were produced using a one-step wet spinning method, 95 which eliminated the need for further protonation. Subsequently, various coagulation solvents (e.g.…”

Cylindrical Self-Assembly and Flow Alignment of Comb-Shaped Supramolecules of Electrically Conducting Polyaniline

“…However, we did not regard a small amount of free AMPSA to be a major problem since, e.g., in the highly conducting fibers the optimal amount of AMPSA is even larger, i.e., nearly 0.6 mol vs PhN-repeat units, which almost certainly contains free AMPSA. 7,8 Next we turn to the complexes with alkylresorcinols. All of the samples PANI(AMPSA) 0.5 (C n res) y with n ) 0, 2, 6 and y ) 0.5, and 1.0 were homogeneous at the resolution of optical microscopy and they showed no evidence of phase separation.…”

“…10 Another development is that PANI complexed with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) gives highly conducting fibers, up to 2000 S/cm, when it is wet spun from dichloroacetic acid. 7,8 In this case, highly purified PANI with high molecular weight was used and the chains were stretched due to the wet spinning process, which may contribute to the high conductivity.…”