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

Abstract

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.

Giant piezoresistivity in aligned carbon nanotube nanocomposite: account for nanotube structural distortion at crossed tunnel junctions

“…[10][11][12][13][14] Consider a 3-dimensional (3D) CNT percolation network model containing uniformly distributed and aligned CNTs in the polymer matrix as shown in Figure 1a and 1b, respectively. The CNT percolation network theory assumes the resistivity of the percolating CNT networks in the composite can be represented by the resistivity of an effective resistor network, where the CNTs that do not participate in conducting current flow are eliminated by the Dulmage-Mendelsohn decomposition.…”

“…44 It is worth to note that CNTs were considered either as ''soft-core" or "hard-core" in the existing percolation network models. [10][11][12][13][14] The former led to a physically incorrect CNT overlap or penetration at CNT junctions, 39 while the latter assumed CNTs as rigid and non-deformable tubes. 45 All of them ignored the effect of CNT structural distortion and thus overestimated the electrical conductivity by orders of magnitude.…”

“…Existing percolation model cannot predict these characteristics correctly, because it considered only two piezoresistive mechanisms of composites under external strain. [10][11][12][13][14] One of the mechanisms is the length change of CNT segments that participate in conducting the current flow in reorientation process. The length change is caused by the movement of CNT junctions.…”

Carbon Nanotubes for Mechanical Sensor Applications

“…Macroscopic approaches are not capable of testing structures of single CNTs; instead, they focus on the creation of macroscopic structures as films, dog bones, or yarns which are tested using macroscopic tensile testing devices Besides this, substrate bending (as shown in Figure ) and three‐ or four‐point bending setups are discussed as alternatives. Besides such classical approaches, studies are presented in which CNT compounds are directly attached to the human body to sense the action of knees, fingers, and facial muscles—which also strains or bends the substrate.…”

Effect of carbon nanotube alignment on nanocomposite sensing performance

“…Khan et al [16] assembled aligned MWCNT-epoxy nanocomposites by applying direct current (DC) of 200-1,200 V. The applied DC voltage allowed CNT bundles to align in the direction of the electric field, and the results showed that aligning MWCNTs resulted in a lower percolation threshold and higher conductivity than composites with randomly distributed MWCNTs. Parmar et al [17] fabricated 5 wt% MWCNT-polycarbonate (PC) composites using injection and compression molding techniques. The electrical resistance of the randomly dispersed MWCNT-PC specimen was lower (740 Ω) than that of the aligned MWCNT-PC specimen (13.9 kΩ).…”