Entradas recentes
Enhanced structural and thermal stability of carbon nanofibre-reinforced wet-spun coaxial phase change fibres with fatty acids
( 2026 ) Hammes, Nathalia; Pinheiro, Inês Marafão Esteves; Júnior, Orlando Sousa Lima; Silva, Maria Manuela; Zille, Andrea; Felgueiras, Helena Prado; Rocha Segundo, Iran Gomes da; Carneiro, Joaquim A. O.
The increasing instability of the energy sector and the rising pressure to reduce carbon emissions have intensified the search for passive solutions that can lower energy use in buildings. Since the thermal properties of construction materials directly influence heating and cooling demands, thermal energy storage has become an important strategy for managing temperature fluctuations and advancing energy efficiency. In this context, phase change materials (PCMs) are particularly appealing because they can store and release thermal energy as latent heat. However, directly integrating PCMs into construction materials may cause leakage, physicochemical incompatibilities, and a decrease in mechanical performance during phase changes. Encapsulation is therefore an effective method for containing the PCM within a protective shell, maintaining its thermal performance, and minimising negative impacts on the host material's structural integrity. In this study, coaxial polymeric phase change fibres (PCFs) were successfully fabricated via wet-spinning, a technique that controls polymer precipitation in a coagulation bath to form continuous core-sheath structures. Linoleic acid (LA) and oleic acid (OA), both fatty acids and PCMs, were used as core materials, while cellulose acetate (CA) reinforced with carbon nanofibres (CNF, 0.05 and 0.10 wt.%) was used as the protective sheath. Bright-field microscopy confirmed the formation of well-defined coaxial structures and showed good dispersion of CNF within the sheath. Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) verified the preservation of chemical structures after processing and confirmed the presence of characteristic fatty acid functional groups in the encapsulated fibres. Thermogravimetric analysis (TGA) revealed a two-stage degradation profile, with fatty acid volatilisation occurring at 230–310 °C and CA decomposition at 310-400 °C. Differential scanning calorimetry (DSC) demonstrated consistent phase change behaviour, with higher melting enthalpy observed in CNF-reinforced PCFs, indicating improved thermal energy storage capacity. Dynamic mechanical analysis (DMA) showed that adding CNF enhanced the stress-strain response and increased the time to failure, suggesting improved structural reinforcement and mechanical stability. Overall, these findings demonstrated that wet-spinning is an effective method for encapsulating fatty acids into coaxial PCFs, while CNF reinforcement offered a promising approach to simultaneously improve thermal energy storage and mechanical strength. The developed composite material is a promising solution for sustainable, energy-efficient use in the built environment.
Thermoelectric analysis of Pyrograf® III carbon nanofiber/polypropylene composites with considerable high positive Seebeck coefficients
( 2026 ) Paleo, Antonio J.; Krause, B.; Mánuel, J. M.; Beltrán, A. M.; Ribeiro, Ana; Cerqueira, M. F.; Muñoz, E.; Melle-Franco, M.; Sanchez-Valdes, S.; Pötschke, P.
This study presents, for the first time, the thermoelectric (TE) properties of as provided Pyrograf® III PR 24 HHT XT carbon nanofibers (CNFs) and their effect on the TE properties of polypropylene (PP) processed by melt mixing with 6% by weight of these CNFs. At 30 °C, the CNFs present a modest σ of ∼37 S m−1 and a considerable high S of ∼40 μVK−1, equivalent to a power factor (PF) of 6 × 10−2 μW m−1 K−2, which makes them the CNFs with the greatest TE properties among the others Pyrograf® III grades. As for the PP/CNF composites, they show lower σ and S at 30 °C, with values of ∼7 × 10−2 S m−1, and ∼ 38 μVK−1, respectively, equivalent to a PF of 1 × 10−4 μW m−1 K−2. From the TE results of the CNFs and their derived PP/CNF composite, a simplified quantum chemical model is applied to investigate the transfer of electrons (n-type doping) from PP to CNFs, concluding that this transfer depends on the adsorption mode of PP molecules and CNFs at their interface. Moreover, the σ of the CNFs and PP/CNF composite show negative temperature effect (NTC) in the interval from 30 to 100 °C, explained as thermally activated hopping mechanism by the 3D variable range hopping (VRH) model, while their S shows nonlinear character, also observed in others Pyrograf® III grades and derived PP/CNF composites, in that interval of temperature. These results are presented with the aim of determining the role played by this type of CNFs, on the thermoelectric properties of the polymer composites melt mixed using them, with a view to their use as p-type materials in thermoelectric generators (TEGs).
Exploring event distributions with a simple granular flow experiment
( 2026 ) Vieira, L. G.
Probability distributions describing random events are central to many areas of physics, from radioactive decay to photon detection. Yet laboratory demonstrations of counting statistics often rely on specialized, costly instrumentation that is unavailable in many educational settings. Moreover, traditional experiments typically present the underlying random processes as a ‘black box,’ limiting students’ ability to connect physical mechanisms with statistical models. This work introduces a simple, inexpensive, and visually transparent experiment in which granules are released from a funnel through manual mechanical shaking and collected on a digital precision balance. Rather than serving merely as a verification tool, the system naturally violates key prerequisites of the classical Poisson distribution due to funnel geometry and granular‑flow mechanics, thereby placing students at the center of active model evaluation. The proposed task offers an accessible introduction to counting statistics, stochastic processes, and data analysis for introductory physics courses.