Synergistic Effect of Dopant Combination and Switchover in Formation Mechanism of Polyaniline Nanowire Subhendu Bhandari, Dipak Khastgir Rubber Technology Centre, Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India Correspondence to: D. Khastgir (E - mail: khasdi@rtc.iitkgp.ernet.in) ABSTRACT: Self-assembled polyaniline (PAni) was synthesized electrochemically in dimethylformamide medium to study the effect of simultaneous use of organic–inorganic dopant combination in aprotic polar synthesis medium. During the synthesis process, simulta- neous dual doping was performed using p-toluenesulfonic acid and sulfuric acid with varying the ratio of the dopants keeping their total concentration unchanged. Nanowire meshes were formed where switchover in nanostructure formation is observed. Nanowire in individually doped PAni was formed with directional joining of smaller nanoparticles or from multilayered tubular nanostructures whereas, for dual doped PAni, either of these two was observed. Periodicity parallel and perpendicular to polymer chain were found in well correlation with diameter of nanowires. Synergistic improvements in AC conductivity, specific capacitance, and thermal degra- dation within certain temperature range were observed in particular ratio of the dopants. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41520. KEYWORDS: conducting polymers; dual doping; electropolymerization; nanostructured polymers; self-assembly Received 11 June 2014; accepted 12 September 2014 DOI: 10.1002/app.41520 INTRODUCTION Control of morphology in self-assembled nanostructured poly- mer is challenge in the field of nanoscience. Differences in mor- phological texture of any polymer synthesized in different conditions are widely reported. Apart from that, the formation of similar nanowires from different assembly motifs at nano- scale may add new direction in the morphological aspect. Intrinsically conducting polymers (ICP) show wide range of morphology 1–4 under different synthesis conditions. Polyaniline (PAni) is an important member of ICP family. It can be a useful component in potential applications like supercapacitor, 5,6 gas sensor, 7–9 corrosion inhibitor, 10 EMI shielding, 11 and so forth, owing to its wide range of electrical conductivity, environmental stability, low cost of synthesis, and so forth. PAni can be synthe- sized in different methods, for example, oxidative polymeriza- tion process, 12 electrochemical polymerization, 13 interfacial polymerization, 14 solid state polymerization (mechanochemi- cal), 15 and so forth. Properties of PAni vary with process parameters. 16,17 Electrical conductivity of PAni depends on oxi- dation state, doping level, and type of dopant. Doping with inorganic as well as organic acids enhances its conductivity. 2,18 Organic and inorganic acids may be used individually 19,20 or simultaneously 21 to prepare electrochemical capacitors. Doping method is crucial for its structure and properties. In secondary doping method, a suitable organic solvent 22 or specially an apparently “inert” material, 23 for example, m-cresol is used as secondary dopant where conventional dopant acts as primary dopant. In dual doping process, two dopants are used one after another. 24 Conversely, two dopants are used at the same time during synthesis of PAni in simultaneous dual doping process where synergy in electrical property may also be achieved. 25 Early reports revealing the formation of different nano and microstructures like rod, 26 sphere, 27 wire, 28 tube, 29 flake, 30 rice- grain, 31 and so forth, in PAni raise the interest about possible formation and transformation mechanism of the morphological structures. In our previous investigation using simultaneous dual doping process in electropolymerization, it has been found that different nanostructured PAni agglomerated to form similar macrospheres. 25 In this work, we have explored switchover in formation mechanism of similar self-assembled nanowires from different nanostructures, which is akin to transformation of multilayers or nanoparticles to tubular structure instead of mere agglomeration as reported in the previous work using the same dopant combination. Earlier report 32 reveals the transformation of layer to tubular nanostructure in supramolecular assembly by tuning the stability of the hydrophilic edges in polar/non-polar solvents. However, the layer-to-tubular transformation has been observed in this work by varying the ratio of dopants without changing the polarity of the solvent. Although, most of the reports on polyaniline follow the synthesis procedure in V C 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2015, DOI: 10.1002/APP.41520 41520 (1 of 9)