High piezoresistivity and its origin in conducting polyaniline/TiO2 composites

Highly piezoresistive conducting polyaniline-titanium oxide (PANI/TiO2) com posites have been synthesized by 'in situ' deposition technique by placing the fine grade powder (average particle size of approximately 100 nm) of an atase TiO2 in the polymerization reaction mixture of aniline. The polyanili ne was formed preferentially on the oxide particles giving a much higher yi eld of polyaniline than in the absence of oxide particles. These composites exhibited high piezosensitivity with the piezosensitivity (S) being maximu m at a certain polyaniline/TiO2 composition. (Our experiments showed that t he piezosensitivity is maximum at 35% of polyaniline with piezosensitivity of the order of 10(3).) The current-voltage (I-V) characteristics of these composites clearly revealed a non-linear space charge controlled charge tra nsport process. A large hysteresis in these current-voltage (I-V) character istics is also observed which in turn is found to depend on composite forma tion (i.e., amount of TiO2 added). The various results have been explained on the basis of the charge transport mechanism in the heterogenous conducti ng material having 'dispersed' semiconducting domains dispersed in it. (C) 1999 Elsevier Science S.A. All rights reserved.