Uncertainties in Electric Circuit Analysis of Anisotropic Electrical Conductivity and Piezoresistivity of Carbon Nanotube Nanocomposites

Abstract

Electrical conductivity and piezoresistivity of carbon nanotube (CNT) nanocomposites are analyzed by nodal analysis for aligned and random CNT networks dependent on the intrinsic CNT conductivity and tunneling barrier values. In the literature, these parameters are assigned with significant uncertainty; often, the intrinsic resistivity is neglected. We analyze the variability of homogenized conductivity, its sensitivity to deformation, and the validity of the assumption of zero intrinsic resistivity. A fast algorithm for simulation of a gauge factor is proposed. The modelling shows: (1) the uncertainty of homogenization caused by the uncertainty in CNT electrical properties is higher than the uncertainty, caused by the nanocomposite randomness; (2) for defect-prone nanotubes (intrinsic conductivity ~104 S/m), the influence of tunneling barrier energy on both the homogenized conductivity and gauge factor is weak, but it becomes stronger for CNTs with higher intrinsic conductivity; (3) the assumption of infinite intrinsic conductivity (defect-free nanotubes) has strong influence on the homogenized conductivity.

Separating Curing and Temperature Effects on the Temperature Coefficient of Resistance for a Single-Walled Carbon Nanotube Nanocomposite

“…Carbon nanotubes (CNTs) enhance polymer properties as a nanofiller and have been promising candidates to increase the electrical conductivities of epoxy-based nanocomposites with high precision and piezoresistive sensitivity [ 3 , 4 , 5 , 6 , 7 ]. Especially in the field of high-precision sensors [ 8 , 9 , 10 ], the influence of environment temperature [ 11 , 12 ] cannot be ignored for multiple polymer functionalities. Considering electrical properties, this phenomenon is commonly related to the temperature coefficient of resistance ( TCR ).…”

“…The CNT intrinsic conductance and tunnelling (or contact) conductance between CNTs are the two basic types of conductance determining the electrical response of a CNT/ polymer nanocomposite [ 14 , 15 , 16 , 17 , 18 ]. Both are complementary one to another [ 9 ] when the leading mechanism of resistance is determined by many factors, first of all, chirality. Besides, the electrical behaviour of CNT networks is significantly influenced by CNT shapes, CNT wall count, functional surface groups, bundling, agglomeration, and CNT deformation at contacts–phenomena that are difficult to be described quantitatively.…”

“…CNT shapes, described by curvature and torsion of their centerlines, also significantly influence the nanocomposite resistance [ 18 ]. Often studies assume a ballistic limit of infinite CNT intrinsic conductance, but detailed analysis [ 9 ] demonstrates that more experimental evidence is required, especially since experiments are often biased by CNT bundling (van der Waals attraction causing single-walled CNTs to form bundles) and CNT agglomeration (entanglement). Moreover, the investigations of humidity effects [ 22 , 23 , 24 , 25 ] show that the resistivity of CNT networks exponentially depends on the development of water absorption.…”

Negative Temperature Coefficient of Resistance in Aligned CNT Networks: Influence of the Underlying Phenomena

“…The CNT minimal contact distance can, in principle, be affected by CNT compression. The effect of this on the homogenized conductivity was evaluated in [ 21 ] and found to be weak; therefore, the value of 0.34 nm is retained in the present calculations.…”

“…In [ 21 ], the present authors compared the influence of parameters defining different conductance mechanisms and found that g intr is the most influential one and has to be fitted in the first place. When this was completed, the use of most common values for the tunnelling resistance and inter-CNT contact distance gave good correspondence with the experimental measurements in [ 8 ].…”