UNCORRECTED PROOF Electrical properties and fractal behavior of polyurethane elastomer/ polyaniline composites under mechanical deformation Erika Hrehorova a , Valery N. Bliznyuk b, * , Alexander A. Pud c , Valery V. Shevchenko d , Kateryna Yu. Fatyeyeva c a Department of Paper Engineering, Chemical Engineering and Imaging, Western Michigan University, Kalamazoo, MI 49008-5462, USA b Department of Materials Science and Engineering, Western Michigan University, Kalamazoo, MI 49008-5462, USA c Institute of Bioorganic Chemistry and Petrochemistry of National Academy of Science of Ukraine, 50, Kharkivske shose, 02160 Kiev, Ukraine d Institute of Macromolecular Chemistry of National Academy of Science of Ukraine, 48, Kharkivske shose, 02160 Kiev, Ukraine Received 24 March 2007; received in revised form 16 May 2007; accepted 22 May 2007 Abstract Present work reports on electrical properties of polyurethane elastomer/polyaniline (PU/PANIeHCl) composite films under tensile deforma- tion. Two types of surface-modified and one type of volume-modified composite of PU and PANIeHCl were prepared. Surface modification of PU film was performed by swelling the parent film in aniline followed by its contact with the acidified oxidant solution to polymerize aniline and form PANIeHCl distributed inside surface/subsurface layer of the film. Volume-modified PU was prepared by mixing of the polymer compo- nents in a joint solution and then solution casting. Nonlinear currentevoltage characteristics were observed for surface-modified samples while linear ones were typical of volume-modified samples. Deformation of the polymer composites caused partially reversible decrease of their con- ductivity characteristics, which could be described mathematically with a power law function of the strain with an exponent being dependable on the type of PU modification. Such behavior was interpreted in terms of deformation of a fractal percolation network formed in the system during its formation and chemical synthesis. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: PU/PANIeHCl composite films; Fractal properties; Q2 Percolation network 1. Introduction During the last decade intrinsically conductive polymers (ICPs) became an efficient alternative to inorganic conductors in many practically important applications. In particular, com- posites based on common polymers and ICPs often possess electrical characteristics (especially being represented as spe- cific ones, i.e., normalized to the material’s specific gravity) highly competitive to those of traditional conductive compos- ite materials in applications as electrode active mass of light- weight batteries, electromagnetic interference shielding, corrosion protection coatings, etc. [1e4]. Due to the occur- rence of additional environmentally dependable properties (smart materials) for some ICPs they can be employed in mod- ern sensor, electrochromic or electro-mechanical actuator devices [5e8]. High electrical conductivity [9], nonlinear electrical or piezo-electric responses [10e12] have been also demonstrated for such composites. These and other publications stressed the crucial role of the morphology, microstructure and type of the matrix polymer on the electrical behavior of conductive polymer composites. For example, as has been demonstrated for PVDF based compos- ites currentevoltage (IeV) characteristics were switching from linear type for the case of ICP component distributed within the volume of the composite film to essentially nonlin- ear type for the case of surface modification (formation of PANIeHCl via polymerization of aniline in a thin surface * Corresponding Q1 author. Tel.: þ1 (269) 276 3213; fax: þ1 (269) 276 3211. E-mail addresses: erika.hrehorova@wmich.edu (E. Hrehorova), valery. bliznyuk@wmich.edu (V.N. Bliznyuk), echoc@mail.kar.net (A.A. Pud), valshevchenko@yandex.ru (V.V. Shevchenko). 0032-3861/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2007.05.065 ARTICLE IN PRESS Please cite this article in press as: Hrehorova E et al., Polymer (2007), doi:10.1016/j.polymer.2007.05.065 Polymer xx (2007) 1e9 www.elsevier.com/locate/polymer + MODEL JPOL11789_proof  6 June 2007  1/9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114