Morphology and electrical properties of intrinsically conducting polymer composites

28 June 2011
A. Sezai Sarac, Suat Cetiner, Hale Karakas, and Fatma Kalaoglu
Polypyrrole-poly(acrylonitrile-co-vinyl acetate) composites are well suited to electromagnetic interference shielding applications, antistatic materials, and decoupling capacitors.

Intrinsically conducting polymer composites (ICPCs) are a novel class of materials that combine the mechanical properties of conventional polymers and the electrical properties of conducting polymers. They can possess relatively high conductivities and dielectric constants, which can be easily tuned from insulating to conducting states through chemical processes. ICPCs are light and flexible relative to metals, and both reflect and absorb electromagnetic radiation.1–3These properties make ICPCs very promising for electromagnetic interference shielding (EMI) and other applications, such as organic solar cells, flexible transparent displays, and supercapacitors.


Atomic force microscopy images of poly(acrylonitrile-co-vinyl acetate)—P(AN-co-VAc)—composites with different polypyrrole (PPy) concentrations: (a) 0wt% (weight percent) PPy and (b) 40wt% PPy. The image area is 3.1×3.1μm.

At present, the main limitations to widespread commercial use of chemically or electrochemically produced conducting polymers is poor mechanical properties and a lack of processibility. Moreover, they are expensive. ICPCs offer a way around these problems. To this end, we have synthesized composites of polypyrrole-poly(acrylonitrile-co-vinyl acetate), PPy-P(AN-co-VAc). We prepared these composites through chemical polymerization of conjugated monomers inside the host polymer matrix, and investigated their electrical properties.

Atomic force microscopy (AFM) indicates that the surface morphology of a poly(acrylonitrile-co-vinyl acetate)—P(AN-co-VAc)—film is porous and relatively smooth: see Figure 1(a). In contrast, polymerization of pyrrole (PPy) on the P(AN-co-VAc) matrix yields grains of various sizes and orientations. The composites have a rough surface with randomly distributed nanosized grains relative to P(AN-co-VAc): see Figure 1(b).

Figure 2 shows the frequency and temperature dependence of AC conductivity for a P(AN-co-VAc) film, as well as a PPy-P(AN-co-VAc) composite film that includes 40wt% (weight percent) PPy. The conductivity increase with respect to temperature indicates semiconductor behavior. The conductivity of the composite is frequency-dependent with a variation that follows a simple power law. The increase at higher frequencies originates from charge motion in the amorphous region, indicating the presence of isolated polarons.4, 5


Three-dimensional plot of the temperature and frequency dependence of real AC conductivity for (a) P(AN-co-VAc) and (b) polypyrrole-poly(acrylonitrile-co-vinyl acetate): PPy-P(AN-co-VAc). Freq: Frequency. Temp: Temperature.

Figure 3 shows M(electric modulus, real component) and M′′(electric modulus, imaginary component) of PPy-P(AN-co-VAc) composites, indicating the relaxation time distribution of conduction. M features a dispersion tending toward infinity, and approaches zero at low frequencies. This indicates that the electrode polarization gives a negligibly low contribution to the electric modulus Mand can be ignored.6 M increases with increasing frequency and decreases with increasing PPy content. Moving the maximum of M′′ toward a higher-frequency region results in a composite of enhanced DC conductivity.


Electric modulus (M)—(a) real component (M) and (b) imaginary component (M)′′—vs. frequency for PPy-P(AN-co-VAc) composites.

In summary, we have investigated the surface morphology and electrical properties of an intrinsically conducting polymer composite. The surface morphology of P(AN-co-VAc) is porous and relatively smooth. In contrast, PPy-P(AN-co-VAc) composites have a rough surface with randomly distributed nanosized grains. The composite conductivity is considerably higher than that of P(AN-co-VAc) itself. The conductivity increase with respect to temperature is indicative of semiconductor behavior. The conductivity behavior of the composite is frequency-dependent, and the variation follows a simple power law. The composite showed improved dielectric properties and AC conductivity. In the future, we will test this composite in applications such as EMI shielding, antistatic materials, and decoupling capacitors.


Authors

A. Sezai Sarac
Istanbul Technical University

A. Sezai Sarac is a professor. His research interests include electronically conducting polymer films as pseudocapacitive electrode materials in supercapacitors, carbon-based microsupercapacitors, nano-structured polymeric composites with electrical and electromagnetic compatibility properties, electrochromic polymeric materials, electrospinning of conductive polymeric composites, as well as nanofibers.

Suat Cetiner
Istanbul Technical University

Suat Cetiner is a PhD candidate. His recent research interests include conductive textile structures, nanostructured conductive polymeric composites, and electrospinning of conductive polymeric composites.

Hale Karakas
Istanbul Technical University

Hale Karakas is an associate professor. Her research interests include fiber technology, synthetic and textured yarn production, as well as textile testing and quality control.

Fatma Kalaoglu
Istanbul Technical University

Fatma Kalaoglu is a professor. Her research interests include electronic and conductive textiles as well as quality control and organization in clothing.


References

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DOI:  10.2417/spepro.003623