Influence of carbon nanotube surface treatment on resistivity and low‐frequency noise characteristics of epoxy‐based composites

Resistivity and low‐frequency (10 Hz–20 kHz) noise characteristics of composite materials with multi‐walled carbon nanotubes (MWCNTs) of different surface treatment, that is, MWCNTs covered with bisphenol‐A based liquid epoxy resin (epoxy‐grafted) and polyethylene polyamine (amino‐grafted), have been carried out over the temperature range from 73 to 380 K. The resistivity of the investigated materials decreases with temperature increase up to 250 K; at higher temperatures polymer matrix expansion leads to the resistivity increase and above 340 K the conductivity in the matrix becomes significant. Low‐frequency noise spectra of the investigated materials are 1/f^α‐type and noise spectral density is proportional to the squared voltage. The observed fluctuations in the investigated materials are resistance fluctuations. The conduction in the investigated composites is caused by tunneling inside and between MWCNTs controlled by charge carrier capture and release processes in localized states. MWCNT's surface treatment by polyethylene polyamine leads to the larger density of surface states what causes lower resistivity and more intensive low‐frequency fluctuations. POLYM. COMPOS., 39:E1224–E1230, 2018. © 2018 Society of Plastics Engineers