Effect of microstructure on the piezoresistive behavior of carbon nanotube composite film

This paper focuses on the piezoresistivity of a nanocomposite film under tensile strain, which consists of continuous carbon nanotube (CNT) network and is synthesized by floating catalyst chemical vapor deposition. The effects of matrix content, film thickness, CNT alignment and purification on the piezoresistive sensitivity of CNT composite film were investigated. The results show that the resistance changes of all these CNT composite films are consistent with the pattern of applied strain, which monotonically increase with increasing tensile strain during loading process. As matrix content increases, the piezoresistive response of CNT composite film becomes less obvious. The thicker composite film shows a bigger gauge factor than the thinner one. For aligned composite film, CNT's intrinsic resistance becomes the controlling factor on the overall resistance change, and its piezoresistivity along aligned direction becomes more sensitive than random composite film. Aligned CNT composite film has an anisotropic piezoresistive behavior. The gauge factor along perpendicular direction to alignment is smaller than that in aligned direction. After purification with hydrochloric acid the piezoresistive behavior becomes more obvious for both random and aligned composite films. The baseline of resistance change shifts towards higher resistance for R-CNT/epoxy, while purified CNT composite film exhibits stable resistance change after 100 cycles. The gauge factors of aligned and random CNT/epoxy composite film after purification are 11.3 and 15.7, respectively. These results reveal the key factors for tailoring piezoresistive response of CNT composite film.