Electrochemical synthesis and properties of layer-structured polypyrrole/montmorillonite nanocomposite films
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Huirong Le School of Engineering, Physics and Mathematics, University of Dundee, Dundee DD1 4HN, United Kingdom (Received 10 November 2009; accepted 22 January 2010)
Layer-structured polypyrrole/montmorillonite (PPy/MMT) naoncomposite films were synthesized by the electrodeposition method. The fabricated free-standing films consist of about 02 wt% Na+-montmorillonite (NMMT). The thickness of films could be controlled by deposition time. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to observe the microstructure of the films. After MMT was introduced into the PPy matrix, the interspace between PPy chains decreased, according to the XRD results. The layered structure of the films was observed from the SEM images. Tensile and nanoindentation test results showed that the mechanical properties of the composite films were improved at low clay loading. The electrical conductivity of the films with 1.2 wt% MMT loading was increased from 3.6 to 51 S/cm, probably because of the restricted growth of PPy chains in the interspace of MMT layers.
I. INTRODUCTION
Polypyrrole (PPy) has attracted broad attention both in industry (e.g., as antistatic coatings) and scientific research since the first electropolymerization was performed by Diaz in 1979.1 Chemical method and electrochemical method are the two main approaches usually used to synthesize PPy materials. Generally, the final product from the chemical method is usually PPy powder, while to prepare PPy thin film, the electrochemical method is preferred. So far, the formation mechanism of PPy is recognized as a cationic radical polymerization. By chemical method, pyrrole monomer is oxidized by an oxidant (e.g., ferric chloride, lithium perchlorate, etc.) before the cationic radical polymerization. In the course of electrochemical deposition, insoluble PPy oligomers interact with the electrode and form a polymeric film in a proper electric field.2 The electrical conductivity of PPy is attributed to the electrons hopping along and across the polymer chains with conjugating bonds. Therefore, longer polymer chains and more coplanarity between interchains are beneficial for obtaining a higher conductivity.3 In the past decade, the synthesis of hybrid inorganic/ polypyrrole composite films has attracted extensive attention for applications in secondary batteries, for example, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0093
658
http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 4, Apr 2010 Downloaded: 13 Mar 2015
LiFePO4/PPy,4 MnO2/PPy,5 maghemite/PPy,6 etc. The introduction of inorganic phases resulted in a great improvement of charge–discharge capacity, but an obvious decrease of electrical conductivity. However, the research by Liu and Ger3 revealed that the conductivity of PPy/ Na+-montmorillonite (MMT) clay composite by the chemical electropolymerization method was significantly increased (20 times higher than that of the virgin PPy film) even though MMT is an inorganic phase with p
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