Begoña Abad

Improved power factor of polyaniline nanocomposites with exfoliated graphene nanoplatelets (GNPs)

In this work, exfoliated graphene nanoplatelets (GNPs)/polyaniline (PANI) nanocomposites have been prepared by sequential processing comprising: (i) a first aniline oxidative polymerization step under acidic conditions and (ii) mechanical blending with GNPs at different percentages. Thermoelectric pellets of the hybrid materials have been obtained at suitable circular geometry by means of cold pressing. Thermoelectric parameters have been determined at room temperature (electrical conductivity, Seebeck coefficient and thermal conductivity). Thermoelectric measurements show a drastic enhancement in both electrical conductivity and Seebeck coefficient with the addition of GNPs. A respectable maximum power factor value of 14 μW m−1 K−2 is reached for hybrid materials charged at 50 wt% GNP content, evidencing a 1000-fold enhancement with respect to the raw PANI polymer. The measured thermal conductivity is in the range of 0.5 W m−1 K−1 for pure PANI to 3.3 W m−1 K−1 for 50 wt% GNP content, which matches the parallel thermal resistor model for this nanocomposite.

Anisotropic Effects on the Thermoelectric Properties of Highly Oriented Electrodeposited Bi2Te3 Films.

Highly oriented [1 1 0] Bi2Te3 films were obtained by pulsed electrodeposition. The structure, composition, and morphology of these films were characterized. The thermoelectric figure of merit (zT), both parallel and perpendicular to the substrate surface, were determined by measuring the Seebeck coefficient, electrical conductivity, and thermal conductivity in each direction. At 300 K, the in-plane and out-of-plane figure of merits of these Bi2Te3 films were (5.6 ± 1.2)·10−2 and (10.4 ± 2.6)·10−2, respectively.

Enhancement of thermoelectric efficiency of doped PCDTBT polymer films

Conjugated polymers may be used as thermoelectric materials due to their low thermal conductivity and have the advantageous characteristics of conventional polymers, such as low weight, non-toxicity and low cost. Here, a detailed investigation into the thermoelectric properties of PCDTBT films is reported. Moreover, in order to improve the thermoelectric properties of this polymer, FeCl3 is used as a doping agent. For the most optimally doped film reported in this work, a power factor value of 24 μW m−1 K−2 is obtained at 150 °C. The different films were characterized by wide-angle X-ray scattering (WAXS) experiments at different temperatures. In order to see the temperature effect, the thermoelectric power factor is measured as a function of temperature from (from RT to 150 °C). Thermal conductivity at room temperature is calculated with two independent methods which give values in agreement within the margin of uncertainty. The results obtained show promise and give insight to motivate future investigation into these types of carbazole derivates.

Tailoring thermal conductivity via three-dimensional porous alumina

Three-dimensional anodic alumina templates (3D-AAO) are an astonishing framework with open highly ordered three-dimensional skeleton structures. Since these templates are architecturally different from conventional solids or porous templates, they teem with opportunities for engineering thermal properties. By establishing the mechanisms of heat transfer in these frameworks, we aim to create materials with tailored thermal properties. The effective thermal conductivity of an empty 3D-AAO membrane was measured. As the effective medium theory was not valid to extract the skeletal thermal conductivity of 3D-AAO, a simple 3D thermal conduction model was developed, based on a mixed series and parallel thermal resistor circuit, giving a skeletal thermal conductivity value of approximately 1.25 W·m−1·K−1, which matches the value of the ordinary AAO membranes prepared from the same acid solution. The effect of different filler materials as well as the variation of the number of transversal nanochannels and the length of the 3D-AAO membrane in the effective thermal conductivity of the composite was studied. Finally, the thermal conductivity of two 3D-AAO membranes filled with cobalt and bismuth telluride was also measured, which was in good agreement with the thermal model predictions. Therefore, this work proved this structure as a powerful approach to tailor thermal properties.