Quasi-static and dynamic strain sensing using carbon nanotube/epoxy nanocomposite thinfilms

Abstract

Thin films are developed by dispersing carbon black nanoparticles and carbonnanotubes (CNTs) in an epoxy polymer. The films show a large variation in electricalresistance when subjected to quasi-static and dynamic mechanical loading. Thisphenomenon is attributed to the change in the band-gap of the CNTs due to the appliedstrain, and also to the change in the volume fraction of the constituent phases inthe percolation network. Under quasi-static loading, the films show a nonlinearresponse. This nonlinearity in the response of the films is primarily attributed to thepre-yield softening of the epoxy polymer. The electrical resistance of the films isfound to be strongly dependent on the magnitude and frequency of the applieddynamic strain, induced by a piezoelectric substrate. Interestingly, the resistancevariation is found to be a linear function of frequency and dynamic strain. Sampleswith a small concentration of just 0.57% of CNT show a sensitivity as high as2.5% MPa−1 for static mechanical loading. A mathematical model based on Bruggeman’seffective medium theory is developed to better understand the experimentalresults. Dynamic mechanical loading experiments reveal a sensitivity as high as0.007% Hz−1 at a constant small-amplitude vibration and up to0.13%/μ-strain at 0–500 Hz vibration. Potential applications of such thin films include highlysensitive strain sensors, accelerometers, artificial neural networks, artificial skin andpolymer electronics.