Thèses

Vendredi 13 Décembre 2024 à 14h00.

Ultrafast heat transfers from Carbon Nanotubes to their environment

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Directeurs de thèse / thesis directors :
Paolo MAIOLI and Natalia DEL FATTI

Membres du jury / jury members :
Tatiana Itina, Rapporteure
Bertrand Audoin, Rapporteur
Frédéric Caupin, Examinateur
Giorgia Fugallo, Examinatrice
Natalia Del Fatti, Directrice de thèse
Paolo Maioli, Co-Directeur de thèse
Matteo Fasano, Invité

Résumé / Abstract :
Carbon-based nanostructures are widely utilized in applications such as light harvesting and energy conversion. The study of their fundamental properties is crucial for efficient device engineering and implementation. Specifically, to accurately predict heat transfer phenomena, it is essential to quantitatively understand the thermal transport at the interface with the external environment. In this context, the Thermal Boundary Resistance (TBR) plays a pivotal role, being the dominant resistance hindering efficient thermal energy exchanges between nano-objects and their surroundings.

In this thesis, we employ ultrafast time-resolved optical spectroscopy, a robust, non-contact, and far-field experimental technique to explore nanoscale heat exchange processes around carbon-based nanostructures. The samples are Carbon Nanotubes (CNTs) in different environments, namely, liquid water, liquid ethanol, and solid water (ice). We develop a finite element method (FEM) thermo-optical model that incorporates time- and temperature-dependent dynamics to reproduce time-resolved experimental signals and quantitatively extrapolate the TBR in each case.

We first quantitatively extract TBR values at the interface between CNTs and water and assess the influence of hydroxyl (-OH) groups covalently bound to the CNTs on TBR. We then examine the impact of the solvent by studying CNTs in ethanol, drawing a comparison with the results observed in water. These experimental findings are evaluated against numerical results from Molecular Dynamics (MD) simulations, developed in collaboration with Politecnico di Torino, which analyze thermal transfer across solid-liquid interfaces involving carbon nanotubes or graphene with water or ethanol. The extracted TBR values are validated, and the influence of surface wettability and interfacial phonon mismatch on the TBR is qualitatively explained. Finally, CNTs are analyzed in different phases of water, liquid at room temperature and solid at -20 °C, demonstrating that ultrafast optical spectroscopy can effectively distinguish between the solid and liquid states of the water surrounding the CNTs, paving the way to future applications. The measurement and analysis protocol developed in this study is versatile and can be applied to various nanofluids and nanocomposite materials.

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