Resistive Response of Carbon-Black-Epoxy Nanocomposites Upon Exposure to Moisture

Abstract

Water ingress in composite structures is an extremely costly problem, and its detection before related damage begins to appear is of utmost importance. Nanocomposites, based on epoxy matrices and Carbon Black fillers (CB), are promising humidity sensors that can be integrated in composite structures during production. Nevertheless, the effects of water uptake on the electrical properties of CB-epoxy films have scarcely been reported. Therefore, this paper sheds light on the resistive response (ΔR/R0) of CB-epoxy film sensors (1.5, 2.5, 3.5 and 4.5 wt%CB) hand-coated and screen-printed on glass substrates, and then conditioned in a moist environment (~ 97 %RH). Films (1.5 wt%CB) based on a filler loading close to the Electrical Percolation Threshold (0.5-1.5 wt%CB) have shown an important increase of their resistance, most likely due to a drop of the tunneling currents. By drawing a parallel between previous work of Fauche et al. (2023) and this study, a Parallel Exponential Kinetics (PEK) model is used and describes very well the kinetics of the resistive responses (water uptake and release regimes), except for the two 2.5wt%CB sensors. In moist conditions, an equilibrium (ΔR/R0)∞ of 53.4% for the hand-coated film and 38.4% for the screen-printed film was estimated for the 1.5wt%CB sensors, and thereby revealing a stronger sensitivity to moisture than films produced by Luo et al. (2007) and Llobet et al. (2014) with a maximum ΔR/R0 of 2.5%. This suggests that CB-epoxy film sensors (≤1.5 wt%CB) have a great potential to detect high relative humidity in composite structures.