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Self-organized structures of the sodium salt of sulfonated polyaniline (prepared from the leucoemeraldine base of polyaniline) in the presence of a mixture of cationic and nonionic surfactants were studied. It was used in the latex form, which has been prepared using a conventional method with sodium dodecyl sulfate. The cationic surfactant used was didodecyl dimethyl ammonium bromide, and the nonionic surfactant used was Triton-X-100. The supramolecular organization was made in aqueous medium by varying the concentrations of the components. A three-dimensional fibrillar network and colloidal aggregate were produced due to the supramolecular organization. The thermal study indicated reversible first-order phase transition in the former cases fulfilling the criteria of thermoreversible gels. A probable explanation of the different morphology from the variation of charge density on the vesicle surface has been offered. The conductivity of fibrillar network is two orders higher than that of the colloidal aggregate. I. INTRODUCTION

Recently, creation of order by a supramolecular organization in a regular fashion has been an important area of material research since material properties are highly affected by this molecular order. In biological systems, the biological activity depends on such molecular ordering. Polymer–surfactant systems are now widely used to produce different supramolecular organized structures.1–11 The self-organization of the polymer chain occurs due to the attachment of the surfactant molecules with the polymer chain by Coulombic attractive forces followed by a delicate balance of attractive and repulsive forces of the surfactant molecules in the medium.4,6,11 If water is chosen as a processing medium of the polymer in the presence of surfactants, the various surfactants may aggregate in the medium as micelles, vesicles, etc., and they may play important roles toward the selforganization of the polymer.2 In this report, we present such a self-organizing system where a different morphology of an important conducting polymer, sulfonated polyaniline (SPAN), may be developed. SPAN is a self-doped conducting polyaniline derivative and has better solubility and thermal stability than hydrochloric acid doped polyaniline (PANI).12,13 It is used in rechargeable batteries14 and light-emitting diodes15 and has the potential for application in electrochemical control of enzyme activity, etc.16 It can be prepared from

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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 7, Jul 2003

both the emeraldine-base (EB) form and the leucoemeraldine-base (LEB) form of PANI.12,13 The LEB–SPAN has a sulfur/nitrogen (S/N) ratio of 0.75 and has one order higher direct current (dc) conductivity than that of EB–SPAN. The main aim of this work is to produce a supramolecular organized structure of this highly important conducting polymer using surfactants. A great deal of research is now going on concerning the formation of colloidal aggregates particularly to produce