Temperature dependent AC conductivity of multiwall carbon nanotube-polystyrene micro-thick composite films

Abstract

Light weight electrically conducting materials that can be fabricated at low cost and are important for certain applications like electromagnetic shielding and field emission devices; carbon nanotubes based-composite materials are most suited for such applications. However, it is quite important to study the temperature dependent electrical behaviour. Here, we are presenting the experimental results on temperature dependent AC conductivity of few hundred micron-thick multiwall carbon nanotube-polystyrene (MWCNT-PS) composites (0.5 & 1.0 wt.%), in the temperature and frequency ranges of 154-293 K and 10 Hz-10 MHz, respectively. The free standing MWCNT-PS composite films were prepared by a simple and cost-effective solution approach, and their good quality was ascertained after characterizing by field emission scanning electron microscopy.For 0.5 wt. % composite film, the conductivity did not show any variation up to 1 MHz at all the temperatures whereas it monotonically increased from 1 MHz to 10 MHz; it followed Jonscher's law. Further, the threshold frequency shifted towards higher frequency with the temperature. The DC conductivity was observed to decrease from 34 µS/cm to 22 µS/cm with variation of temperature from 293 to 154 K, respectively; this decrease of DC conductivity is attributed to increase of activation energy of charge carriers at low temperatures. Interestingly, AC conductivity of 1.0 wt. % sampledid not exhibit any frequency dependence at any temperature; however, DC conductivity reduced to 37 µS/cm (154 K) from 70 µS/cm (293 K).