Electrical properties and fractal behavior of polyurethane elastomer/polyaniline composites under mechanical deformation

Present work reports on electrical properties of polyurethane elastomer/polyaniline (PU/PANI-HCl) composite films under tensile deformation. Two types of surface-modified and one type of volume-modified composite of PU and PANI-HCl 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 PANI-HCl distributed inside surface/subsurface layer of the film. Volume-modified PU was prepared by mixing of the polymer components in a joint solution and then solution casting. Nonlinear current-voltage 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 conductivity 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. (c) 2007 Elsevier Ltd. All rights reserved.