Finite Element Investigation of the Influence of Porosity and Resin Infiltration on the Electrical Conductivity of Carbon Nanotube Yarns

Carbon nanotube (CNT) yarns (CNTYs) are porous fibers with a myriad of applications based on their electrical response. This study presents an electrical finite element model of the cross section of CNTYs, comprising smaller hierarchical elements (CNT bundles) arranged in a hexagonal pattern. The model captures the most relevant mechanisms explaining the effect of porosity and resin infiltration on the electrical conductivity of the CNTY and reproduces experimental data. The porosity is generated with a random algorithm that avoids void clustering. The model assists in explaining factors that modify the electrical resistivity of the CNTY when a liquid polymer infiltrates it. The model suggests that the electrical resistivity of the CNTY increases in a sigmoidal fashion with increased porosity, with the highest electrical sensitivity occurring between 40% and 60% porosity. The experimental findings on the porosity effect are better reproduced if the bundle diameter concomitantly changes with the yarn's porosity. The CNTY's electrical resistivity strongly depends on the electrical resistivity of the infiltrating liquid and on the extent of infiltration. The outer 20–30% CNTY radius is the most sensitive to infiltration. High electrical sensitivity is predicted during the first polymerization stages of a thermosetting polymer resin infiltrating the CNTY.