Conducting polymer composites: novel materials for gas sensing Rupali Gangopadhyay, Amitabha De * Chemical Sciences Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Calcutta 700064, India Abstract A polypyrrole PPy)-based conducting composite was prepared by electropolymerising pyrrole within crosslinked matrix of polyvinyl alcohol) PVA). It was obtained in the form of coherent ®lm and was characterised with respect to different electrical properties. The composite was found to possess signi®cant NH 3 sensing capacity; results of some preliminary investigations regarding the NH 3 sensing is reported here. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Polypyrrole; Gas sensors; Polyvinyl alcohol) 1. Introduction Conducting polymer composites can be prepared ef®- ciently by electrochemical polymerisation technique. Con- ducting polymers are electrosynthesised in presence of an insulating polymer to form the composite. Most convenient techniques for electrosynthesis of composites is to cover the electrode anode) with a conventional polymer prior to the electrodeposition of the conducting polymer on it. The polymer used for this purpose should be insoluble in the polymerisation medium but the ®lm should not be too brittle to allow the solvent and the monomer molecules through it. In this technique, a host of polymers, namely, polyvinyl chloride) PVC) [1], rubber [2], polycarbonate [3], poly- vinyl alcohol) PVA) [4,5], polyacrylonitrile) PAN) [6], polyamides and imides [7], polyether ketone) PEK) [8], naf®on [9], etc. have been combined with PPy and PAn. Each of these efforts have signi®cantly modi®ed the phy- sical and mechanical properties of PPy from different aspects and have rendered them suitable for application in different devices. In the present work, pyrrole was electropolymerised within the matrix of crosslinked PVA to form a good quality composite, studies on different electrical properties and gas sensing capability of which has been discussed here. 2. Experimental 2.1. Preparation of sample A 5% solution of PVA was prepared in 0.5 N HCl and 0.2 ml formaldehyde HCHO) were added to 2.0 ml of the PVA solution to crosslink it. Anode of the electrochemical cell was coated with this solution and was dried in air and was washed several times in methanol and was dried again at 50  C. The coated electrode was immersed for some time in the electropolymerisation bath prior to the polymerisation of pyrrole. Polymerisation was carried out galvanostatically for 1 h in aqueous medium using sodium styrene sulphonate SS) as the electrolyte in argon atmosphere. Concentration of SS was ®xed at 0.02 M. PPy, grown electrochemically within the crosslinked PVA PVA-C) ®lm, was peeled off from the electrode, dried and subjected to different char- acterisations. 2.2. Electrical characterisations and gas sensing Electrical characteristics of the samples were obtained by measuring the voltage drop developed on application of a constant current. For dc measurements, a digital multimeter Yokogawa, 7562) and a constant current source Lake Shore Cryotonics, Model 120) were used. The ac electrical characteristics were measured with two probe method by a precision RCL bridge Quad Tech 7600) at spot frequencies from 20 Hz to 2 MHz and spot voltages from 20 mV to 3 V. The ac measurements were acquired and controlled with a personal computer by means of GPIB interface. Initial electrical characteristics were stabilised by exposure to Sensors and Actuators B 77 2001) 326±329 * Corresponding author. Fax: 91-33-337-4637. E-mail address: amitde@nuc.saha.ernet.in A. De). 0925-4005/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0925-400501)00719-5