Palestrante
Descrição
Every day humanity uses more than a million Terajoules of energy, mostly from fossil fuels. Needless to say that the usage of fossil fuels has been linked to the rising levels of greenhouse gases in the Earth’s atmosphere and is one of the leading contributors to climate warming. This scenario must change. For years a crucial technology that is an important candidate to join the team of renewable and green solutions was out of the spotlight. This is the Seebeck Generator or, simply, Thermoelectrical Generator. Such a generator relies on the difference of temperature to generate electrical current. Basically, a temperature gradient throughout the material results in heat flow, causing the diffusion of charge carriers from the hotter to the cooler zone. Most of the materials currently applied as a thermoelectric platform are based on metals alloys as well as inorganic semiconductors, such as bismuth telluride. However, recently conjugated polymers have also joined the pallet of available materials for thermoelectric applications, especially due to the possibility of an easy-to-manufacture flexible thermoelectric generator. In metals and most inorganic semiconductors, there is a relation between the thermal conductivity (κ) and the electrical conductivity (σ), known as the Wiedemann-Franz law.(1)This relation states that the ratio between the thermal and the electric conductivities is proportional to the temperature, with the constant of proportionality being independent of the system. The main question that arises here is: what is the correlation between the electronic and thermal conductivity in a conjugated polymer? In this research project, we intend to study the validity of the Wiedemann-Franz Law for conjugated polymers. The most commonly used and developed p-type material for thermoelectric applications is PEDOT:PSS and its derivatives, which will be used as our prototype materials. For the thermal conductivity measurements, Thermal Mirror technique (TM) will be performed.(2) TM is a pump and probe method which considers the laser induced surface deformation. The amplitude of the deformation is directly related to the optical absorption and the linear thermal expansion coefficients, and the time evolution of the deformation depends on the heat diffusion properties. The technique is a nondestructive, remote and high-sensitive photothermal method, capable of measuring thermal properties such as thermal expansion and thermal conductivity. For the measurements of electrical conductivity, we plan on using the well-established four-probe measurement.(3) The method requires equally spaced four probes, which are placed in contact with the material to be analyzed. A current source is connected between the two outer probes and a current is applied to them. This process will generate a voltage difference between the two inner probes. Knowing the applied current, the difference of potential between the inner probes and the distance between probes, it is possible to calculate the resistivity/conductivity of the material. Knowing κ and σ for PEDOT:PSS, we will study the validation of the Wiedemann-Franz Law.
Referências
1 FRANZ, R.; IEDEMANN, G. Ueber die Wärme-Leitungsfähigkeit der Metalle. Annalen der Physik,v.89, n.8,1853. doi:10.1002/andp.18531650802.
2 ZANUTO, V. S. et al. Thermal mirror spectrometry: an experimental investigation of optical glasses. Optical Materials, v.35,n.5, p.1129-1133,2013. doi:10.1016/j.optmat.2013.01.003.
3 GIROTTO, E. M; SANTOS, I. A. Medidas de resistividade elétrica DC em sólidos: como efetuá-las
corretamente. Quimica Nova, v.25, n.4, p.639-647,2002. doi:10.1590/S0100-40422002000400019.
| Subárea | Física da Matéria Condensada |
|---|---|
| Apresentação do trabalho acadêmico para o público geral | Não |
