Article Dans Une Revue Journal of Physical Chemistry B Année : 2024

Thermal Conductivity of a Fluid-Filled Nanoporous Material: Underlying Molecular Mechanisms and the Rattle Effect

Nikolas Ferreira de Souza
  • Fonction : Auteur
Luís Fernando Mercier Franco
  • Fonction : Auteur
Benoit Coasne

Résumé

Nanoporous materials are central to the energy/environmental crisis with key applications in adsorption, separation, and catalysis. While confinement and surface effects on fluids severely confined in their porosity are well-documented, the thermal behavior of nanoporous solids subjected to fluid adsorption remains puzzling by many aspects. With striking phenomena such as the so-called rattle effect through which fluid/solid collisions decrease the overall thermal conductivity, the thermal conductivity and, more generally, heat transfer and dispersion in these complex systems challenge classical approaches (e.g. mixing rules including effective medium approaches fail to capture such effects as shown here). In particular, a robust 1 molecular framework to describe the crossover between thermal conductivity decrease through the rattle effect in very narrow pores to the thermal conductivity increase when replacing vacuum by a fluid phase in larger pores is still missing. Here, using a prototypical model of fluid-filled nanoporous materials (a Lennard-Jones phase confined in an all-silica zeolite), we perform a molecular simulation study to shed light on the parameters that govern the rattle effect in nanoporous solids. First, by varying the fluid/fluid, fluid/solid and solid/solid interaction strengths as well as the fluid number density and mass density, we unravel the ingredients that lead to the essential coupling between fluid adsorption and phonon transport. Second, despite this complex interplay, inspired by pioneering molecular approaches on the rattle effect, we show that all data obey a simple statistical physics model which relies on the change in the speed of sound due to the fluid adsorbed density and the decrease in phonon lifetime due to scattering by fluid molecules. This framework, which provides a simple formalism to rationalize the thermal behavior of this class of solid/fluid composites, points to a thermal conductivity decrease upon fluid confinement (up to 30% in some cases). Such effect paves the way for the design of novel applications involving fluids in interaction with nanoporous materials.

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hal-04730490 , version 1 (10-10-2024)

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Nikolas Ferreira de Souza, Cyril Picard, Luís Fernando Mercier Franco, Benoit Coasne. Thermal Conductivity of a Fluid-Filled Nanoporous Material: Underlying Molecular Mechanisms and the Rattle Effect. Journal of Physical Chemistry B, 2024, 128 (10), pp.2516-2527. ⟨10.1021/acs.jpcb.3c07088⟩. ⟨hal-04730490⟩

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