Hydrogen bubble-assisted syntheses of polypyrrole micro/nanostructures using electrochemistry: structural and physical property characterization

Polypyrrole (PPy) in the family of pi-conjugated polymers is a potential candidate for microscopic actuators, electrochromic devices, batteries, and drug delivery systems. We report the controlled syntheses of PPy micro/nanocontainers through electrochemical generation of H-2 bubbles from a surfactant cum electrolyte beta-NSA (beta-naphthalene sulfonic acid) stabilized on the working electrode, followed by electrochemical polymerization of monomer (pyrrole) around the wall of the micelles serving as template. It is noticed that the density, shape, caliber, and thickness of self-assembled PPy micro/nanocontainers can be regulated by electrochemical potential window for H2 bubbles and number of cyclic voltammetric scans for the electropolymerization of pyrrole. Sodium chlorate and perchlorate are used to synthesize conventional PPy films. By changing the dopant structure, one can control the microscopic structure and physical properties, which are analyzed using multiple microscopic techniques and X-ray diffraction (XRD), infrared, vis Raman and X-ray photoelectron spectroscopic analytical tools. In light of this information, an exhaustive description of the material is attained. Experimental results show that the films consist of spherical/globular surface morphology and cup-bowl-like structures, which becomes lantern-like with increasing cyclic voltammetry scans. The bowl diameter and caliber and room temperature conductivities range 0.05-60 mu m, 5-50 mu m and 2 x 10(-2)-20 S cm(-1), respectively. Raman spectroscopy (RS) helps to identify the oxidized PPy; polaron and bipolaron states and thus a detailed molecular structure. The results also showed that the relative conjugation length increases with decreasing size of the morphological feature. Moreover, these studies enhanced the understanding of bubble nucleation at the solid-electrolyte interface. Copyright (C) 2008 John Wiley & Sons, Ltd.