Anisotropic Thermal Transport in Thermoelectric Composites of Conjugated Polyelectrolytes/Single-Walled Carbon Nanotubes

Abstract

We report a method to determine the thermal conductivities of polymer composites with single-walled carbon nanotubes (SWNTs) using time-domain thermoreflectance. Both through-plane and in-plane thermal conductivities were determined. Two types of CPEs used in these studies are of the same conjugated backbone but with either cationic (CPE-PyrBIm 4 ) or anionic (CPE-Na) pendant functionalities. The CPE-Na/SWNT composites are p-type conductors, whereas the CPE-PyrBIm 4 /SWNT counterparts exhibit ntype charge transport. The CPE/SWNT films were prepared through a filtration method that preferentially aligns the SWNTs in the in-plane direction. Attaching the composites onto glass substrates with a precoated heat transducer allows one to measure the through-plane thermal conductivity of materials with rough surfaces. The in-plane thermal conductivity can be measured by embedding thick samples into epoxy followed by microtoming to expose the relatively smooth cross sections. The thermal conductivity along the in-plane direction is found to be higher than that along the through-plane direction. Indeed, the anisotropy factor of thermal conductivity in these composites is approximately an order of magnitude, favoring in-plane direction.

Farming thermoelectric paper

“…We now turn to the thermal properties, and in particular, we are interested in determining if the characteristic low thermal conductivity of the porous bacterial cellulose of about 0.5 W m –1 K –1 35,36 is retained in the composites. To avoid misinterpretations related to possible anisotropic behavior,19 we have measured the thermal conductivity in-plane by using Raman thermometry 47. This method uses a laser to simultaneously excite the resonant Raman signal and heat the sample.…”

“…highly conductive thick films are required for efficient thermoelectric generators). An alternative to high doping levels consists in adding conductive fillers such as carbon nanotubes (CNTs) to the organic semiconductor matrix;11–16 an approach that has already successfully yielded ZT ≈ 0.2 13,17–19. The polymer matrix acts as a binder for the otherwise airborne hazardous CNTs, while providing additional doping paths and a reduced thermal conductivity 18,20.…”

“…Different types of polymer matrices have been recently employed in thermoelectric composites, including conjugated polymers21 non-conjugated polymers,22 water-soluble conjugated polyelectrolytes19 and multicomponent polymeric matrices 6. While very promising in terms of thermoelectric performance, these systems still lack some desirable traits.…”

Thermoelectrics: From history, a window to the future

“…The inclusions can be nanostructured inorganic thermoelectric materials, such as for example Te-nanowires, metal nanowires, or carbon-based fillers, such as graphene and carbon nanotubes (CNTs). In these composites, the matrix material serves to bind the filler together, while also conferring additional benefits, such as a lowered κ, [629,630] a tunable doping level, [631] solution processability [623], reduction of overall cost or flexibility compared to bulk films of neat filler. [632] Due to their versatility, polymers are often the matrix of choice.…”

Percolation and Transport Properties in The Mechanically Deformed Composites Filled with Carbon Nanotubes

“…Nowadays, the the critical study points are the determination of the properties of composites filled with the carbonaceous fillers, like carbon nanotubes (CNT) [1][2][3][4], or graphene nanoplatelets (GNP) [5][6][7][8]. All these objects have high aspect ratios, and there is an interest to develop anisotropic composites using the partially oriented fillers [9][10][11]. There are several ways to reach the anisotropy in case of a CNT-filled composite, for instance: mechanical deformation, curing the CNT-filled polymer in external fields, or template-based techniques (see [12] and Refs therein).…”