Mechanism of charge transport in poly(2,5-dimethoxyaniline)

Abstract

Poly͑2,5-dimethoxyaniline͒ ͑PDMA͒ has been synthesized by chemical oxidative polymerization technique using varying ratio of oxidants; ferric chloride ͑FeCl 3 ͒ and ammonium persulfate ͓͑NH 4 ͒ 2 S 2 O 8 ͔, in an inert atmosphere at low temperature ϳ278 K. The synthesized samples of PDMA have been characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and by measuring its dc conductivity ͑ dc ͒. The temperature dependence of dc conductivity of PDMA samples has been examined in the wide temperature range 6-303 K. The analysis of dc conductivity data reveals that in the temperature range ϳ100-303 K, the dc conductivity is predominantly governed by Mott's three-dimensional variable range hopping, however, below 100 K tunneling seems to dominate. Different Mott's parameters such as characteristic temperature ͑T 0 ͒, density of states at the Fermi level ͓N͑E F ͔͒, the average hopping distance ͑R͒, and the average hopping energy ͑W͒ have been estimated for all the PDMA samples and are in good agreement with the values reported earlier for other conjugated polymers.

Mechanism of direct current electrical charge conduction in p-toluenesulfonate doped polypyrrole/carbon composites

“…The observed trend in r dc vs. 1000/T appears similar to those reported earlier for other conjugated polymers. 17,19,20,24,[27][28][29][30][31][32] The dc conductivity r dc (Fig. 7) can be given 13,45 by the following relation:…”

“…12 But before such PPy/C composites could be used for device applications, it was thought worthwhile to examine in detail the mechanism of dc electrical charge conduction in this composite system. Different conduction models, similar to those developed for amorphous semiconductors, 13 have been proposed [14][15][16][17][18] to explain the mechanism of dc electrical charge conduction in conducting polymers; however, the different types of structural and electronic defects as well as lack of long range ordering in these systems do not allow to explain the mechanism of charge transport completely. Kivelson 14 was first to propose a model to explain the mechanism of conduction in polyacetylene wherein the charge transport occurs between neutral and charged solitons at iso-energetic levels.…”

“…15 The other two models, widely used to explain the dc conductivity of conjugated polymeric systems, are fluctuation induced tunneling (FIT) 16 and Mott's variable range hopping (VRH) conduction. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] In FIT conduction model, 16 the tiny conducting domains, formed during doping in a granular system, participates in the delocalization of charge carriers by tunneling between conducting metallic islands. However, the macroscopic conductivity in most of the conjugated polymeric systems is assumed to result from the hopping conduction process.…”

“…However, when the carrier localization is not strong, the charge carriers jump to the sites for which the required activation energy is small and resides farther away, then the charge transport occurs by VRH. 13,23 It is worthwhile to mention here that the Mott's VRH conduction model has been applied to explain the dc conductivity of many conjugated polymeric systems such as doped polyacetylene, 25,26 polyanilines, 27,28 poly(2,5-dimethoxyaniline), 17 polypyrroles, 18,[21][22][23]33 poly(3-methylthiophene), [29][30][31]34 poly(3-hexylthiophene), 19 and poly(3-octylthiophene), 20,32 carbon-black/polypyrrole nanocomposites. 35 Several studies on dc conduction of different conducting polymers and their composite systems are available in literature.…”

“…35 Several studies on dc conduction of different conducting polymers and their composite systems are available in literature. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] However, there is no report available on temperature dependence of dc electrical conductivity in pTS doped PPy/C composites.…”