Electrical and dielectrical properties of the percolating system polystyrene/polypyrrole particles L.C. Costa a, * ,F.Henry b , M.A. Valente a , S.K. Mendiratta a , A.S. Sombra c a DepartmentofPhysics,UniversityofAveiro,3810-193Aveiro,Portugal b O.M.M.,C.N.R.S.,94320Thiais,France c DepartmentofPhysics,FederalUniversityofCear a,Fortaleza,CE,Brazil Received 23 November 2001; received in revised form 28 December 2001; accepted 11 January 2002 Abstract Percolation is a commonly observed phenomenon in the properties of many composite materials. In two-phase materials,wheretheelectricalconductivityofthedispersephaseissignificantlydifferentthanthatofthehostphase,the conductivity versus concentration (of the dispersed phase) shows a percolation behaviour. Withthemainaimofcontrolthepercolationthreshold,inordertooptimisetheRadarelectromagneticabsorption, new composite materials were prepared, based on polystyrene (PS) and polypyrrole (PPy) particles. The percolation criticalconcentrationwascontrolled,changingtheratioofthesizeofthatparticles,andthiswillbepresentedinanext communication. Inthispaperwereportthedcconductivity(r dc ),withappliedfieldsupto100kVm 1 ,andthecomplexpermitivitty (e 0 , e 00 )atlowfrequencies(1mHz < f < 500Hz),atconstanttemperature T ¼ 300K,ofoneofthatcomposites(ratio diametersizeofPSandPPyparticlesofabout3.3),withdifferentconcentrationofdispersedPPyconductingparticles. Apercolationthreshold,intheconductivity,wasobservedatavolumeconcentrationabout12%ofPPy.Atthesame concentration, the behaviour of the complex permitivitty changes significantly, and the Cole–Cole plot (e 00 versus e 0 ) shows a clear asymmetry for concentrations higher than the percolation threshold. Ó 2002 Elsevier Science Ltd. All rights reserved. PACS: 72.80.Tm; 77.22.Gm; 77.84.Lf Keywords: Electrical conductivity; Dielectric response; Percolation 1. Introduction In the last few years the dielectric constant spectro- scopyhasproventobeaveryusefultoolforstudyingthe structure and the dynamics of polymeric systems [1–4]. Thisknowledgeisalsoimportantforthedevelopmentof new materials for industrial applications, with specific electrical properties. Particularly, the conducting poly- mers have been proposed for use as conducting wires, electromagnetic shielding materials [5,6], light emitting diodes [7], sensors [8], etc. The electrical conductivity of an insulating polymer can be altered by adding conducting particles like car- bon [9–11], iron [12], nickel [13] or another conducting polymer [14–16]. The conductivity of the composite materialcanthusbecontrolledbyproperlychoosingthe components, their shape and their relative concentra- tions. Polypyrrole (PPy) is one of the most interesting con- ducting polymers because it exhibits high conductivity [17],andcanbeeasilyintroducedinapolymericmatrix. The composites formed with low contents of PPy dem- onstrate reasonable high conductivities [18]. On the otherhand,polystyrene(PS)isasuitablehostbecauseit isreadilyavailable,andiseasytocastintodesiredforms maintaining the mechanical integrity of the matrix. European Polymer Journal 38 (2002) 1495–1499 www.elsevier.com/locate/europolj * Corresponding author. Tel.: +351-234-370-944. E-mailaddress: kady@fis.ua.pt (L.C. Costa). 0014-3057/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0014-3057(02)00044-7