Effect of CNT alignment on the strain sensing capability of carbon nanotube composites

The effect of carbon nanotube (CNT) alignment on the strain sensing capabilities of multi-walled carbon nanotube/polycarbonate (MWCNT/PC) composites was investigated. Injection and compression molding techniques were used to fabricate 5 wt% MWCNT/PC composites. The effects of these molding techniques on the alignment of the MWCNTs were observed through micrographs obtained from transmission electron microscopy (TEM) and investigated quantitatively using the electrochemical impedance spectroscopy (EIS) technique. A one-dimensional piezoresistive model was developed to predict the changes in the resistance of the MWCNT/PC composites with respect to the applied strain. The strain sensing capabilities of the composites were examined along the lengths and widths of the samples through tensile testing, and gauge factors were calculated to compare the strain sensitivities. A linear correlation was observed between the resistance change and the applied strain when subjected to tension, and the composite samples fully recovered to their unstressed states upon unloading. A sensitivity factor defined by relating the analytical model and experimental data provided an indirect measure of the degree of MWCNT alignment in the composite. From the results obtained, it was evident that the injection molded samples, which exhibited high alignment, showed higher gauge factors than the compression molded samples. The highest gauge factor was found in the injection molded samples perpendicular to the MWCNT alignment. (paper)