Synthetic Metals 146 (2004) 121–126 “Switching effect” in pressure deformation of silicone rubber/polypyrrole composites J. Vilˇ cáková a , M. Paligová a , M. Omastová b , P. Sáha a , O. Quadrat c,∗ a Faculty of Technology, Tomas Bata University in Zl´ ın, 762 72 Zl´ ın, Czech Republic b Polymer Institute, Slovak Academy of Sciences, 842 36 Bratislava, Slovak Republic c Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic Received 20 November 2003; received in revised form 3 March 2004; accepted 20 April 2004 Abstract Conductive silicone rubber/polypyrrole composites were prepared by cast molding of polymer matrix components and chemically synthesized polypyrrole (PPy). Composites contained from 2.2 to 8.5vol.% of PPy. The sigmoid dependence of the conductivity of original uncompressed sample on the filler was found and PPy percolation threshold concentration lower than 4 vol.% was estimated. Electrical conductivity of silicone rubber/polypyrrole composites in pressure deformation showed a steep decrease more than five orders of magnitude to values corresponding to an insulator. This “switching effect” had a good reproducibility, which suggests a possible use of this material in microelectronics. © 2004 Elsevier B.V. All rights reserved. Keywords: Silicone rubber; Polypyrrole; Composites; Pressure deformation; Electrical conductivity 1. Introduction Composites of electrically conducting particles in non-conducting polymer matrix are materials increasingly important for variety of practical application [1]. Their possible using as resistors in microelectronic devices, heat- ing elements, electrically conductive adhesives, films and foams, or plastics dissipating static charges, has attracted much attention and stimulated a great deal of research ac- tivity in the past years. In this field a lot of work have been focused on composites filled with particles of electrically conducting polymers [2], such as polyaniline, polypyrrole or polythiophene, which, due to a possible control of their intrinsic conductivity, make it possible to obtain materials with required electrical properties. Especially polypyrrole (PPy) showed high mechanical and thermal resistance and its composites proved promising for practical use. This poly- mer is easy to prepare by oxidative pyrrole polymerization. Thus, poly(butadiene-co-acrilonitrile)/PPy composite was obtained by electrochemical polymerization, using rubber ∗ Corresponding author. Tel.: +420-296-809-351; fax: +420-296-809-410. E-mail address: quadrat@imc.cas.cz (O. Quadrat). coated electrode as a substrate [3]. After rinsing the prepared composite with the appropriate solvent rubber could be com- pletely washed away, producing partially oriented polypyr- role. Also an elastomeric poly(epichlorohydrin-co-ethylene oxide)/polypyrrole blends were prepared electrochemically [4]. Results of differential scanning calorimetry study of prepared composites suggest an association of the guest con- ductive polymer with the ethylene oxide blocks of the rubber copolymer host. Stress–strain measurements show that the conductive polymer guest increases the rigidity and tough- ness of the elastomer host. Semi-interpenetrating networks of PPy and ethylene-propylene-5-ethylidene-2-norbornene rubber (EPDM) were prepared by two methods. In one of them, rubber was mixed with oxidant CuCl 2 and dicumyl peroxide, cross-linked by heating, and exposed to pyrrole vapour [5]. The conductivity of this composite was nearly equal to that of pure rubber. In the second method, EPDM rubber was swollen in FeCl 3 solution in tetrahydrofuran, and then exposed to pyrrole vapour [6]. Conductivity of com- posites prepared following this method was reported to be higher. The present studies revealed that the transport of charge carriers between conducting particles appreciably depends on their distribution in polymer matrix, in addition to particle 0379-6779/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.04.028