Influence of nanomaterial parameters on the thermoresistivity and electrical conductivity of hybrid conglomerated CNT/GNP piezoresistive polymer strain sensors

Abstract

Temperature dependence of resistance known as thermoresistivity and sharp enhancement of electrical conductivity known as percolation are unique electrical properties affected by temperature and agglomeration of carbon nanotubes (CNTs), respectively. An investigation of the thermoresistivity of a hybrid agglomerated CNT-graphene nanoplatelet (GNP) polymer strain sensor is conducted, taking into account the tunneling mechanism. Rod-like CNTs and disk-shape GNPs are used to generate the representative volume element for evaluating the piezoresistivity caused by the strain and thermoresistivity induced by temperature. The percolation model predicts the tunneling conductance based on contacts that exist inside conductive channels. It is demonstrated that percolation occurs at a GNP concentration of 1.3 vol% when the GNPs have a lateral size of 1 μm, which represents their largest dimension. The effects of CNT aspect ratio and agglomeration radius, and orientation state on the sensitivity of the piezoresistive strain sensor are analyzed. It is found that the piezoresistivity of the 1 vol% CNT polymer nanocomposite increases by 60 % at 1.5 % strain when the orientation state shifts from randomly oriented to partially aligned or when the aspect ratio changes from 370 to 250. The comparison shows that resistance drops as temperature increases because thermal activation hopping becomes more dominant than the thermal expansion of the matrix. A 1 vol% CNT/polymer nanocomposite with 20 nm diameter CNTs with average length of 1.5 μm experiences a 40 % reduction in resistance over a 110 °C temperature increase. © 2025 Elsevier B.V.