Thermoelectric properties of n-type poly (ether ether ketone)/carbon nanofiber melt-processed composites

• Autor(a) principal: Paleo, Antonio J.
• Data de Publicação: 2022
• Outros Autores: Krause, Beate, Soares, Delfim, Melle-Franco, Manuel, Muñoz, Enrique, Pötschke, Petra, Rocha, A. M.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: https://hdl.handle.net/1822/82718
• topic: Carbon nanofibers; Poly(ether ether ketone); Conductive polymer composites; Seebeck coefficient; Variable-range hopping; Electronic doping; Science & Technology

The thermoelectric properties, at temperatures from 30 °C to 100 °C, of melt-processed poly(ether ether ketone) (PEEK) composites prepared with 10 wt.% of carbon nanofibers (CNFs) are discussed in this work. At 30 °C, the PEEK/CNF composites show an electrical conductivity (σ) of ~27 S m⁻¹ and a Seebeck coefficient (S) of −3.4 μV K⁻¹, which means that their majority charge carriers are electrons. The origin of this negative Seebeck is deduced because of the impurities present in the as-received CNFs, which may cause sharply varying and localized states at approximately 0.086 eV above the Fermi energy level (E_F) of CNFs. Moreover, the lower S, in absolute value, found in PEEK/CNF composites, when compared with the S of as-received CNFs (−5.3 μV K⁻¹), is attributed to a slight electron withdrawing from the external layers of CNFs by the PEEK matrix. At temperatures from 30 °C to 100 °C, the σ (T) of PEEK/CNF composites, in contrast to the σ (T) of as-received CNFs, shows a negative temperature effect, understood through the 3D variable-range hopping (VRH) model, as a thermally activated hopping mechanism across a random network of potential wells. Moreover, their nonlinear S (T) follows the same behavior reported before for polypropylene composites melt-processed with similar CNFs at the same interval of temperatures.