High piezoresistivity and its origin in conducting polyaniline/TiO2 composites

Highly piezoresistive conducting polyaniline–titanium oxide (PANI/TiO2) composites have been synthesized by `in situʹ deposition technique by placing the fine grade powder (average particle size of approximately 100 nm) of anatase TiO2 in the polymerization reaction mixture of aniline. The polyaniline was formed preferentially on the oxide particles giving a much higher yield of polyaniline than in the absence of oxide particles. These composites exhibited high piezosensitivity with the piezosensitivity (S) being maximum at a certain polyaniline/TiO2 composition. (Our experiments showed that the piezosensitivity is maximum at 35% of polyaniline with piezosensitivity of the order of 103.) The current–voltage (I–V) characteristics of these composites clearly revealed a non-linear space charge controlled charge transport process. A large hysteresis in these current–voltage (I–V) characteristics is also observed which in turn is found to depend on composite formation (i.e., amount of TiO2 added). The various results have been explained on the basis of the charge transport mechanism in the heterogenous conducting material having `dispersedʹ semiconducting domains dispersed in it.