Improving electron transport and mechanical properties of polyaniline-based composites

11 November 2015
Do Sung Huh and Chitragara Basavaraja
Doping polyaniline with well-dispersed poly(3,4-ethylenedioxythiophene) increases the composite conductivity due to the increased mobility of charge carriers.

Conducting polymers have various industrial, scientific, and medical applications. As coatings, they offer electromagnetic shielding, anti-corrosion, and anti-static properties. Due to their high conductivity, they are found in transistors, light-emitting diodes, and solar cell batteries. These materials are attractive because of their controllable conductivity, high-temperature resistance, low cost, and easy bulk preparation.1, 2 Polyaniline (PANI) is the most studied conjugated conducting polymer because of its remarkable electron-transport properties, mechanical flexibility and environmental stability. Due to the interesting redox properties of its nitrogen atoms, it is possible to control PANI's conductivity via acid/base modification.

However, the practical use of PANI has been limited by its nonfusibility (it is not easily miscible), insolubility in aqueous solution, and poor mechanical characteristics. Typically, the poor mechanical properties of conducting polymers can be overcome by mixing with other polymers. However, this process can reduce their conductivity as the addition of macromolecular chains can disrupt the charge transfer path. An alternative approach is the use of PANI in blends with conducting or conventional polymers. New materials possessing improved processability, flexibility, and controllable conductivity can be obtained by blending PANI with other polymers or fillers.3–6 The goal of our research was to improve the electrical conductivity and mechanical stability of PANI-polymer composites by doping PANI with a conducting polymer.

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a conducting polythiophene derivative discovered by Heywang and coworkers.7 It is very reactive, enabling high levels of doping to generate highly electrical conductive materials, and is also almost transparent and highly stable in films. It consists of 3,4-disubstituted thiophene rings and has been widely used because its promising electrical conductivity due to its low band gap, transparency, and thermal and environmental stability.8–11 Given its six-membered dioxane ring structure, the oxygen-bearing substitute could offer stability for free radicals and positive charges by intermolecular delocalization.11–13 PEDOT is a relatively rigid polymer with solid-state packing at a characteristic face-to-face distance (010) of ~0.34nm, which is similar to graphite.

We prepared PANI-PEDOT composites by the co-polymerization of aniline with 3,4-ethylenedioxythiophene (EDOT) via in situ deposition, with aniline dispersed in aqueous medium using ammonium persulfate (APS) as an oxidizing agent. The method is shown in Figure 1. We used a known amount of EDOT, and different aniline concentrations of 0.5, 0.75, and 1.0M designated as PEDOT-PANI-1, PEDOT-PANI-2, and PEDOT-PANI-3, respectively. The precipitated PANI-PEDOT polymer composite was filtered and washed with distilled water and acetone until the wash was colorless. The polymer was dried at 50–60°C in an oven overnight.


Polyaniline-poly(3,4-ethylenedioxythiophene) (PANI-PEDOT) composite film fabrication method. EDOT: 3,4-Ethylenedioxythiophene. APS: Ammonium persulfate. NMP: N-Methyl-2-pyrrolidone.

Figure 2 shows temperature-dependent conductivities of nanocomposite films for PANI and PEDOT-PANI-1, PEDOT-PANI-2, and PEDOT-PANI-3 in the range of 293–473K. The conductivities of PANI and PEDOT-PANI nanocomposites increase as temperature increases. At room temperature, the electrical conductivities of PANI and PEDOT-PANI-1, PEDOT-PANI-2, and PEDOT-PANI-3 were 0.000795, 0.00994, 0.02039, and 0.03597S cm−1. However, they increased to 0.023, 0.28, 0.59, and 1.08S cm−1 at 493K. These results indicate that the inclusion of PEDOT polymer in PANI positively affects the conductivity of PANI nanocomposites, possibly due to the combined effect of the incorporated PEDOT and PANI conducting polymer.


Temperature-dependent conductivities of PANI and PANI-PEDOT nanocomposites from 293 to 473K. The increased conductivity of the composites is attributed to increased charge-carrier mobility resulting from PEDOT doping of PANI.

In summary, to improve the conductivity of pure PANI via doping with another conducting polymer, PANI nanopolymer composites containing well-dispersed PEDOT were prepared by in situ chemical polymerization of aniline hydrochloride in an aqueous APS solution. To understand the conduction behavior of the composites, their temperature-dependent electrical conductivity was measured in the range of 293–473K. The increased conductivity of the composites is attributed to the mobility of increased charge carriers induced by the doping of PEDOT in the PANI polymer. Our results suggest that these composites have potential application in electronic devices, sensors, and functional coatings.


Authors

Do Sung Huh
Inje University

Chitragara Basavaraja
Inje University


References

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DOI:  10.2417/spepro.006131



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