Raman spectroscopy and resistance-temperature studies of functionalized multiwalled carbon nanotubes/epoxy resin composite film

Nowadays, flexible sensors and electronics accelerate the development of conductive polymer composites (CPCs). Carbon nanotube (CNT)-based epoxy resin CPCs could lead to possible breakthroughs for engineering applications because of the relatively high mechanical stiffness of this material. In this work, a flexible temperature sensor prototype was prepared from multiwalled carbon nanotubes (MWNTs)/epoxy resin CPC film. The flexible interdigital electrode was integrated to decrease the resistance of the composite film from 10 MΩ to 300 kΩ. The strain in the MWNTs was quantitatively measured by Raman spectroscopy. Temperature dependence of the composite film resistance exhibited clear positive temperature coefficient (PTC) and negative temperature coefficient (NTC) phenomena. The glass transformation temperature of the composite was determined by dynamic mechanical analysis. Finally, a segmented model concerning the entire resistance-temperature relation of the composite was established, and a possible mechanism was proposed according to the synergistic effect between tunneling conduction and electron thermal fluctuation. The segmented equation provided here may be useful for further sensor optimization and theoretical modeling based on such MWNTs/epoxy resin CPCs.