Matrix Dominated Positive/negative Piezoresistance in Conducting Polymer Nanocomposites Reinforced by CNT Foam

Conducting polymer nanocomposites filled with carbon nanotubes (CNTs) have attracted great interest in developing flexible sensors. This paper reported the preparation of cotton-based CNT foam by using a chemical vapor deposition method. The prepared foam was incorporated into epoxy or polydimethylsiloxane (PDMS) to fabricate corresponding nanocomposites. The results showed that CNT foam exhibited excellent adsorption performance for liquid polymer, thus eliminating the variations on the dispersion, concentration and formation of CNT networks in nanocomposites. CNT/Epoxy nanocomposites had a comparable electrical conductivity (1.2 S/m) with that of CNT foam (1.5 S/m), and a much higher value than that of CNT/PDMS counterpart (0.06 S/m). Interesting, CNT/Epoxy showed a negative piezoresistance, whereas the one with PDMS had a positive effect. It was found that the Poisson's ratio of the matrix and its wettability with nanofiller controlled the contact and tunneling resistance in the system, which in turn affecting piezoresistive behavior of bulky nanocomposites.