Alternating-Current Properties of Elastomer-Carbon Nanocomposites** By Maris Knite,* Valdis Teteris, Ilze Aulika, Heinz Kabelka, and Armin Fuith Regardless to widespread technological use of electrically conductive polymer composites [1] fundamental and applied studies of the materials are still of acute interest. Conductive polymer composites are obtained when particles of good con- ductors (carbon black, graphite powder, carbon fibres, micro- particles of metals) are implanted into an insulating polymer matrix. Most often such polymer composites are used as the so-called inactive materials in electric heating elements and resistors. Recently efforts have been made [2,3] to obtain active polymer composites the conductivity of which would depend on external thermodynamic parameters Ð pressure, tempera- ture, and other. A new generation of cheap large-size sensors might be developed on the basis of such materials. New interesting properties are expected in case the com- posite contains dispersed nano-size conducting particles. In earlier studies [4,5] reversible change of conductivity by more than four orders has been observed in a composite containing 10 mass parts of extra-conductive carbon black nano-particles (ECBN) in polyisoprene matrix. In other words, a giant tenso- resistance effect is observed in the nanocomposite. Analysis of conductivity and dielectric permittivity as functions of applied AC frequency and features responsible for the giant tenso-resistance effect [4] in polyisoprene-ECBN composites are presently reported. A continuous insulator-conductor transition is observed at gradual increase of the number of randomly dispersed con- ductor particles in an insulator matrix. Most often such tran- sitions are described by the model of statistical percolation [6] and called percolation transitions. The volume concentration of conductor particles V C at which the transition proceeds is called the percolation threshold or the critical point. Accord- ing to the model, conductor particles, in the vicinity of V C , as- semble in clusters the correlation radius n (average distance between two opposite particles of a cluster) diverges as n ~ |V±V C | ±m (1) upon approaching V C . [6] In agreement with the general scaling principle of the per- colation theory, the relative dielectric permittivity of a two- component system (hereafter ± the composite) at low AC fre- quencies, [7] approaching the percolation threshold from both sides, diverges as n: e ~ |V±V C | ±s , V<V C , V>V C (2) ADVANCED ENGINEERING MATERIALS 2004, 6, No. 9 1 Knite et al./Alternating-Current Properties of Elastomer-Carbon Nanocomposites DOI: 10.1002/adem.200400063 ± [*] jPlease check title and addresses of authors!j Prof. M. Knite, Dr. V. Teteris Institute of Technical Physics Riga Technical University Azenes Str. 14/24, LV-1045 Riga (Latvia) E-mail: knite@latnet.lv Dr. I. Aulika Institute of Solid State Physics University of Latvia Kengaraga Str. 8, LV-1063 Riga (Latvia) Dr. H. Kabelka, Dr. A. Fuith Institute of Experimental Physics University of Vienna Strudlhofgasse 4, Vienna 1090 ( Austria) [**] The authors are thankful to Aris Solovjovs and Janis Barloti for preparing the samples. The research has been supported by the Council of Science of Latvia.