Piezoresistive response of carbon nanotube composite film under laterally compressive strain

Carbon nanotubes (CNTs) have attracted great attention for strain sensor application due to their excellent electromechanical property. This paper focused on the piezoresistive response of high CNT loading composite film. The piezoresistive behavior of floating catalyst chemical vapor deposition (FCCVD)-grown CNT composite film under tension and lateral compression was investigated and compared with a graphite composite film. The effects of matrix type, functionalization and acid treatment on piezoresistive response of CNT composite film were discussed. The results showed that CNT composite film exhibited positive piezoresistive response under tension and negative piezoresistive effect under lateral compression. After eliminating the effect of geometrical deformation on gauge factor, the change in resistivity was more sensitive under lateral compression than under tension. Different from CNT composite film, graphite composite film showed less obvious piezoresistive behavior, and showed positive piezoresistive response regardless of tensile and laterally compressive loads. Furthermore, the piezoresistive response of CNT composite film was found to closely correlate with its modulus. Stronger interfacial bonding was proved to effectively enhance the piezoresistive response and increase the corresponding gauge factor. CNT/epoxy composite film with 1 h treatment in potassium permanganate solution reached a gauge factor of −5.9. These results revealed the key factors tailoring piezoresistive response of CNT composite film, and presented one potential approach to monitor biaxial strain. The present work should be useful in the in-plane strain monitoring by incorporating the CNT film into traditional composite.