Studies on electropolymerization of aniline in the presence of sodium dodecyl sulfate and its application in sensing urea Mandakini Kanungo, Anil Kumar, A.Q. Contractor * Department of Chemistry, Indian Institute of Technology, Bombay, Mumbai 400076, India Abstract In this paper, we report a detailed investigation of the effect of varying concentrations of sodium dodecyl sulfate (SDS) on the rate of polymerization of aniline. Quantitative analysis of the data is done in order to propose a probable mechanism for the growth of polyaniline (PANI) in presence of SDS (SDS  /PANI). The SDS  /PANI films were characterized by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM), in situ conductance, in situ UV  /vis spectroscopy and scanning electron microscopy (SEM) and were contrasted with polyaniline prepared under identical conditions in the absence of SDS. The polymerization rate was found to decrease initially with increase in concentration of SDS; it passes through a minimum at 1.5 mM and then increases rapidly on further increasing the SDS concentration. EQCM studies showed that the polymerizing species is a charge transfer complex formed between SDS and aniline. Leaching out of SDS was observed during redox cycling of the SDS  / PANI films, which results in the formation of a porous polymer film allowing more inclusion of ions. This was further confirmed by observing a higher transport rate of urea across SDS /PANI coated membrane. These porous polyaniline films were then used as transducer for sensing urea. Keywords: PANI; SDS /PANI; Microstructure; Urea sensor 1. Introduction Conducting polymers are novel organic semiconduct- ing materials with great promise because of their wide range of potential technological applications. This include their applications in storage batteries [1,2], electrochromic devices [3,4], light emitting diodes [5], non-linear optics [6], as a corrosion inhibitor [7] and in a variety of sensors including chemical [8,9] and biosen- sors [10  /12]. The understanding of the nature of these polymers is of utmost importance for developing electrochemical devices. Among the conducting poly- mers, polyaniline has been studied extensively due to the commercial availability of the monomer, its easy synth- esis, well-behaved electrochemistry, good environmental stability, high conductivity and multiple redox and protonation states [13]. Normally intractable polyaniline can be made pro- cessable either by making it soluble by doping it with organic sulfonic acids [14,15] or by the preparation of polyaniline in colloidal form [16]. Polymeric as well as non-polymeric surfactants have been used to make colloidal polyaniline. The presence of a surfactant or polyelectrolyte significantly modifies both the micro- scopic and macroscopic properties of the final polymer [16  /27]. Polyaniline films prepared in the presence of poly (vinyl sulfonate) remain conducting even in neutral solution [18], whereas polyaniline itself becomes insulat- ing at pH higher than 4. Sodium dodecyl sulfate (SDS) has been used extensively as a surfactant for micellar/ emulsion polymerization of aniline using both chemical and electrochemical polymerization routes [17,21  /27]. An enhancement in the rate of polymerization was observed in the presence of SDS and this has been attributed to the high local concentration of aniline monomer in the micellar reaction medium. However, the SDS concentrations used for these studies were much higher than the cmc of SDS under the experimental conditions. Interestingly, Albuquerque Maranhao and