Preparation of polyaniline nanofibers and nanoparticles via simultaneous doping and electro-deposition Subhasis Roy a , Kajari Kargupta b, ⁎ , Saikat Chakraborty a , Saibal Ganguly a,1 a Department of Chemical Engineering, Indian Institute of Technology, Kharagpur Kharagpur-721302, India b Department of Chemical Engineering, Jadavpur University, Kolkata-700032, India Received 26 July 2007; accepted 18 December 2007 Available online 5 January 2008 Abstract We present a new post-synthetic method for producing different nano-structures of Polyaniline (PANI), especially nano-fibers and nano- particles of varying doping (oxidation) states, by simultaneous doping and electro-deposition from electrolyte solutions of undoped PANI (Emeraldine bases) and p-toluenesulphonic acid using constant applied voltage and varying deposition time. High Resolution Transmission Electron Microscopy analysis reveals that during the initial doping-dominated stage continuous connected conductive PANI Emeraldine salt nano- fibers of diameter less than 50 nm are formed while in the later deposition-dominated stage, 30-50 nm sized isolated dispersed nano-particles of non conductive Leuco-Emeraldine are formed. © 2007 Elsevier B.V. All rights reserved. Keywords: Polymer; Nanomaterials; Nanofibers; Nanoparticle; Doping; Electro-deposition 1. Introduction Due to their unique electrical, electrochemical and/or optical properties, Electrically Conducting Polymers (ECPs) are finding applications in controlled drug release, optoelectronics, micro- electronics, bioelectronics, paints and coatings, etc. The ECPs are often called ‘conjugated polymers’ because of their macromole- cular property, with the presence of a spatially extended π-bond that engenders their intrinsic semi-conductive nature [1]. Electro- chemical switching of the polymer is accompanied by movement of counter ions, and conjugated polymers usually become electrically conductive through occurrence of doping phenom- enon. Polyaniline (PANI), among the other organic conjugated polymers, owes its popularity to its high conductivity in the doped state and its excellent thermal and electrochemical stability. Synthesized PANI typically consists of macromolecular cations (protonated emeraldine bases) and dopant counter-ions that they take up from the electrolyte medium/reaction mixture for the sake of charge neutralization. The physicochemical characteristics of PANI, thus, depend on the nature of both the macromolecular cations and the counter-ions. The transition of PANI from its most reduced, insulating form of Leuco-emeraldine through its half- oxidized, semi-conductive form of Emeraldine salt to its fully oxidized, insulating form of Pernigraniline base is accompanied by strong color change from transparent pale yellow through green to violet, respectively. The blue Emeraldine base form can be easily doped by means of protonic acid treatment to obtain the protonated, green Emeraldine salt, which is electrically conductive [2]. Such variation of electrical conductivity with the extent of doping accompanied by an optical effect makes PANI an attractive material for sensors and optoelectronic applications [3–5]. Most of the recent research on PANI is directed towards production and characterization of nanomaterials, because of their particle size and morphology-dependant physicochemical properties. Methods have been developed to shape PANI into nanostructures by introducing “structural templates” (e.g. nanoporous membranes and micelles) to the polymerization reaction [6–8]. Recently, the polymerization reaction pathway Available online at www.sciencedirect.com Materials Letters 62 (2008) 2535 – 2538 www.elsevier.com/locate/matlet ⁎ Corresponding author. Tel.: +91 9932246712; fax: +91 33 2414 6378. E-mail addresses: subhasis1093@yahoo.com (S. Roy), kajari.kargupta@rediffmail.com (K. Kargupta), saikat@che.iitkgp.ernet.in (S. Chakraborty), sganguly@che.iitkgp.ernet.in (S. Ganguly). 1 Presently working as Technical Advisor, N.M.R.L., D.R.D.O., Ministry of Defence, India. 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.12.066