Enhancement of thermoelectric conversion efficiency of polymer/carbon nanotube nanocomposites through foaming-induced microstructuring

Semiconducting-based materials such as bismuth antimony are current thermoelectric (TE) materials of choice because of their superior TE efficiency, which can be characterized by the dimensionless figure of merit (ZT). However, factoring the cost, weight, and environmental concerns, polymeric TE material systems have become attractive alternatives despite their lower ZT values. The potential to tailor the flexibility of polymeric TE materials also represent another key advantage, especially for wearable electronics. One of the key challenges to enhance their ZT values is the need to simultaneously increase the electrical conductivity and the Seebeck coefficient, while supressing the thermal conductivity. In this research, physical foaming is suggested as an innovative and effective processing strategy to circumvent this challenge. Multi-walled carbon nanotube (MWCNT)/high density polyethylene (HDPE) nanocomposite foams were fabricated as a case example. Experimental results showed that introducing cellular structures in MWCNT/HDPE nanocomposites, loaded with 15 wt % MWCNT, would result in a 600-fold increase in their ZT values. This great improvement was achieved through significantly reducing their effective thermal conductivity, while simultaneously increasing their electrical conductivity and Seebeck coefficients. The findings have proven that foaming can serve as a novel strategy to enhance the efficiency of various polymeric TE materials. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45073.