Vol.:(0123456789) 1 3 Applied Physics A (2018) 124:38 https://doi.org/10.1007/s00339-017-1467-3 Thermal and electrical conductivities of epoxy resin-based composites incorporated with carbon nanotubes and TiO 2 for a thermoelectric application Congliang Huang 1,2  · Wenkai Zhen 1  · Zun Huang 1  · Danchen Luo 1 Received: 8 October 2017 / Accepted: 9 December 2017 / Published online: 13 December 2017 © Springer-Verlag GmbH Germany, part of Springer Nature 2017 Abstract For a thermoelectric application, the thermal conductivity, electrical conductivity and fgure of merit of epoxy resin-based composites incorporated with carbon nanotubes and TiO 2 are investigated in this paper. First, the composite is prepared with a solution blending method. Then, the structure, thermal and electrical conductivities are characterized with experimental methods. Finally, the thermal conductivity, electrical conductivity and fgure of merit are discussed. Results turn out that with an increasing content of carbon nanotube fllers, there are diferent changing trends of thermal and electrical conduc- tivities because of large diference between thermal and electrical contact resistances in the composite. With the increasing fller content, the electrical conductivity increases exponentially while thermal conductivity saturates to be a constant value. Due to the large ratio of electrical to thermal conductivities, the fgure of merit with 8 wt% of fllers is more than 50 times larger than that with a low content of fllers. Our results confrm that the recently proposed concept of ‘electron-percolation thermal-insulator’ is a feasible way to enhance the fgure of merit of a polymer composite. 1 Introduction Thermoelectric materials have drawn a wide attention due to their large advantage in realizing energy conversation with- out moving mechanical components and harmful gas emis- sion [1–8]. The thermoelectric performance of a material is characterized by a fgure of merit ZT = S 2 T / , where S is the Seebeck coefcient, σ is the electrical conductivity, κ is the thermal conductivity. Because σ and κ are commonly coupled together according to Wiedemann–Franz law, it is usually difcult to increase σ and decrease κ simultaneously. To solve this problem, some special composites or com- pounds are proposed, such as the so-called phonon-glass/ electron-crystal compounds [9, 10], multilayer flms [11] and others [12–16]. Most recently, a concept “electron-per- colation thermal-insulator” was proposed for designing a polymer-based thermoelectric composite [17]. ZT enhance- ment of this kind of thermoelectric material is based on the diferent changing trend of thermal and electrical conduc- tivities with an increasing fraction of fllers. As a thermo- electric material, polymer-based composites also meet the requirements of future applications that are geared toward personal and portable polymer-based fexible electronics [18, 19], and additionally possess properties of light weight, chemically stability, good fexibility, and easy preparation in solution [20]. In this paper, we validate the idea (electron- percolation thermal-insulator) with an experimental method. First, we prepared the epoxy resin-based compos- ites incorporated with only multi-wall carbon nanotubes (MWCNT@epoxy-resin), and incorporated with MWC- NTs and TiO 2 particles simultaneously (MWCNT + TiO 2 @ epoxy-resin). The TiO 2 particles are added to impede the aggregation of MWCNTs in MWCNT + TiO 2 @epoxy-resin nanocomposites. And then, the structures, thermal and elec- trical conductivities of composites are characterized with experimental methods. Finally, the thermal conductivity, electrical conductivity and ZT are all discussed. It turns out that the ZT of MWCNT + TiO 2 @epoxy-resin composites can be greatly enhanced with a large content of CNT fll- ers, because of the large increase of electrical conductivity * Congliang Huang huangcl@cumt.edu.cn 1 School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221116, People’s Republic of China 2 Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309, USA