Piezoresistance characterization of poly(dimethyl-siloxane) and poly(ethylene) carbon nanotube composites

This study examines the piezoresistive behavior of polymer-carbon nanotube composites. Piezoresistive composites of poly(dimethyl-siloxane) (PDMS) and poly(ethylene) (PE) filled with multiwall carbon nanotubes (MWNTs) were prepared. The morphology and the electrical conductivity of the composites were characterized at various MWNT compositions. The percolation threshold was found to be 3 wt% for PDMS composites and 2.2 wt% for PE composites. The piezoresistive behavior under compression was measured using a setup comprised of a mechanical tester and a digital sourcemeter. Negative piezoresistive behavior was observed, signifying a reducing mean interparticulate distance in the composites. The PE-MWNT composites were found to be more sensitive than the PDMS composites (97% versus 78% change in resistance), which was attributed to the dissimilar morphologies as a result of difference in processing. Increasing the MWNT concentration in the PE composites resulted in decreasing the sensitivity to stress. The results were found to fit well to a modified version of a piezoresistance model. PDMS and PE composites were found to have different piezoresistance behavior during stress relaxation and cyclic loading. The resistance of PE, in comparison to PDMS, was less prone to changes in stress during stress relaxation and exhibited greater sensitivity and less drift during cyclic loading.