Coupled Effects of Film Thickness and Filler Length on Conductivity and Strain Sensitivity of Carbon Nanotube/Polymer Composite Thin Films

The coupled effects of varying composite film thicknesses and filler lengths on the conductivity and strain sensitivity of carbon nanotube (CNT)/polymer composite films are investigated through modeling and experiments. Change in average intertube distance is calculated statistically through the Monte Carlo simulations for samples with different CNT concentrations and film thicknesses for a given filler aspect ratio. The composite conductivity is then estimated from the intertube distance with a semi-analytical model based on a tunneling current. The dependence of conductivity on mechanical strain is investigated for varying film thickness for strain sensor applications. A partial alignment of CNTs introduced at film thicknesses less than the CNT length is observed to have a significant influence on the composite conductivity and strain sensitivity, specially at low CNT concentrations. The modeling results can explain the observed experimental results of conductivity for CNT composites, which illustrate a unique dip in conduction with increasing thickness. These results are important for understanding the composite characteristics with different filler orientations and film thicknesses for a given filler length, and useful for the design optimization of high performance composite electronic films for applications in electronic skin and sensors.