Preparation of polypyrrole microstructures by direct electrochemical oxidation of pyrrole in an aqueous solution of camphorsulfonic acid
Introduction
Intrinsically conducting polymers (ICPs) are a new generation of polymers, because they cover the full range from insulator to metal and retain the attractive mechanical properties as well as the processing advantages of polymers [1], [2], [3]. Therefore, conducting polymers have been extensively explored as alternatives to metals or inorganic semiconductors in the fabrication of microelectronic, optoelectronic, and microelectromechanical devices [4], [5], [6]. Most of the applications in microsystems require the formation of patterned microstructures of conducting polymers. Up to now, a number of techniques have been developed for microstructuring ICPs, such as laser-induced polymerisation, laser ablation, polymerisation on a prestructured substrate and soft lithography [7], [8], [9], [10]. Microtubules and microspheres of ICPs can be prepared via a template or a template-free route [11], [12], [13], [14], [15], [16], [17], [18], [19]. Although aligned microstructures based on the features of the template can be produced, the template-guided synthesis technique is expensive and the solid template limits the size of the material. Therefore, synthesis of aligned ICP microstructures with the desired morphology without using a solid template has been a challenge for a long time.
On the other hand, polypyrrole (PPy) is an intrinsically conducting polymer with various interesting properties such as high conductivity, good thermal and environmental stability, and biocompatibility [20]. Microstructured polypyrrole is useful for fabricating microdevices including reactors, actuators and sensors [14], [21], [22], [23].
In this paper, we report a novel electrochemical route to prepare well-aligned three-dimensional polypyrrole (PPy) microstructures. The formations of the unusual microstructures were due to the fact that the self-assembled gas bubbles on the working electrode acted as the template.
Section snippets
Experimental
(+)- and (−)-Camphorsulfonic acids (Fluka, Japan) were used as received and pyrrole (Chinese Army Medical Institute, Beijing, China) was used after distillation. The growth of polypyrrole (PPy) microstructures was carried out at room temperature in a one-compartment cell (5 cm3) (except as mentioned otherwise in the text) by the use of a Model 283 potentiostat–galvanostat (EG&G Princeton Applied Research) under computer control. The working and counter electrodes were two stainless steel sheets
Morphology
Fig. 1 shows typical scanning electron microscopic (SEM) images of PPy microstructures obtained by electrolysis of 0.5 M pyrrole in 0.6 M (−)-camphorsulfonic acid ((−)-CSA) aqueous solution at different applied potentials for 240 s each. It is clear from this figure that the microstructures stand upright on the electrode surface and align fairly well in a high density. Micro-cups (Fig. 1(A)) with a diameter of ca. 60–80 μm and height of ca. 100 μm were formed at a low applied potential of 0.8
Conclusions
Polypyrrole microstructures with very unusual morphology can be generated by electropolymerization of pyrrole in an aqueous solution of camphorsulfonic acid. The shape and size of the microstructures can be modulated electrochemically. The microstructures are made of PPy in the doped state. The PPy films with microstructures showed strong and broad redox waves in the electrolyte of aqueous (+)-or (−)-camphorsulfonic acid solution because of their large surface areas. The growth process of the
Acknowledgments
We thank the National Natural Science Foundation of China for supporting this work (Nos. 50073012, 50225311, 50133010).
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2020, Progress in Organic CoatingsCitation Excerpt :Gas bubbles produced in-situ during electropolymerization can act as a soft template, thus eliminating any hard or pre-formed template to direct growth of tubular features. In the literature, templateless electropolymerization of pyrrole in water (H2O) has been specifically studied [25–33]. The formation of porous structures is induced by the release of gas bubbles (H2 and/or O2) while a surfactant is necessary to stabilize them and induce the polymer growth around them.