Synthetic Metals 145 (2004) 23–29 Nanofibers of polyaniline synthesized by interfacial polymerization Xinyu Zhang a , Roch Chan-Yu-King b , Anil Jose b , Sanjeev K. Manohar a,∗ a Alan G. MacDiarmid Laboratory for Technical Innovation, Department of Chemistry, The University of Texas at Dallas, Richardson, TX 75083, USA b University of Science and Arts of Oklahoma, Chickasha, OK 73018-5322, USA Received 5 December 2003; received in revised form 17 March 2004; accepted 29 March 2004 Available online 10 June 2004 Abstract The average diameter of polyaniline nanofibers obtained by interfacial polymerization using a solution of aniline in toluene as the top organic phase and acidic ammonium peroxydisulfate as the bottom aqueous phase can be controlled by using surface active dopants and/or surfactants in the aqueous phase. The average diameter of polyaniline nanofibers doped with camphorsulfonic acid (CSA) synthe- sized by interfacial polymerization decreases when twin-tailed anionic surfactants, based on the cis-1,2-alkylethene sulfonate structure (alkyl = C 5 H 11 or C 7 H 13 ), are used. For example, the average diameter of polyaniline. CSA nanofibers decreases in the order 48 nm (no surfactant)> 35 nm (C 5 H 11 -twin-tailed)> 28 nm (C 7 H 13 -twin-tailed). This effect is reversed in polyaniline nanofibers synthesized using 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) as the dopant, e.g., the average fiber diameter of polyaniline. AMPSA increases in the order 23 nm (no surfactant)< 35 nm (C 5 H 11 -twin-tailed)< 55 nm (C 7 H 13 -twin-tailed). The doping percentage is reduced when surfactants are used although there is no significant change in the pressed-pellet room temperature 4-probe DC conductivity compared to conventional (single-phase) polyaniline·HCl (σ ∼ 1–5 S/cm). Polyaniline nanofibers also show increased capacitance consistent with their high surface area, e.g., a capacitance value of 277 F/g was observed in nanofibers of polyaniline·AMPSA (23 nm average diame- ter) compared to 11 F/g in non-fibrillar polyaniline·AMPSA powder. Further optimization and surfactant structure–function evaluation is needed to uncover the mechanism associated with this phenomenon. © 2004 Elsevier B.V. All rights reserved. Keywords: Interfacial polymerization; Nanofibers; Polyaniline; AMPSA; CSA; Twin-tailed surfactants 1. Introduction We describe the influence of dopants and surfactants on the morphology and related properties of polyaniline nanofibers synthesized by the recently reported interfacial polymerization method in which aniline is chemically ox- idatively polymerized to polyaniline at the interface of two immiscible liquids [1]. Unlike conventional (single-phase) aqueous chemical oxidative polymerization, interfacial polymerization of aniline using organic dopants like cam- phorsulfonic acid (CSA) results in polyaniline powder with fibrillar morphology having average fiber diameters <100 nm. Interfacial polymerization is the latest among a variety of approaches to chemically synthesize nanostructured elec- tronic polymers [2]. These include the use of physical (insol- uble) templates such as zeolites [3], opals [4] and controlled ∗ Corresponding author. Tel.: +1-972-883-6536; fax: +1-972-883-6586. E-mail address: sanjeev.manohar@utdallas.edu (S.K. Manohar). pore-size membranes [5], etc., and chemical (soluble) tem- plates such as surfactant micelles [6,7], emulsions [8–10] and polymers [11,12]. Recently, a “non-template” method has been described in which large organic dopant anions are used during the reaction [13–16]. These bulky organic anions are believed to have “surfactant-like” properties and form aggregates in solution which act as pseudo-templates for fibrillar polymer growth. Conducting polymer nanofibers and nanotubes with diameters in the range of 650–80 nm have been obtained using this approach. Nanofibers have also been reported during the electrochemical polymer- ization of aniline in the presence of sulfonated porphyrin aggregates [17]. Interfacial polymerization can therefore be regarded as a non-template approach in which high local concentrations of both monomer and dopant anions at the liquid–liquid interface might be expected to promote the formation of monomer–anion (or oligomer–anion) aggregates. These aggregates can act as nucleation sites for polymerization resulting in powders with fibrillar morphology. In this study, we describe the synthesis and characterization of 0379-6779/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.03.012