Thermal properties of solid-liquid nanocomposites ; Propriétés thermiques des nanocomposites solide-liquide

The solid-liquid hybrid systems are extensively present in various industrial applications. Furthermore, with the rapid development of nanomaterials elaboration, it is possible to fabricate series of nanostructured and nanoporous materials with confined liquid. Consequently, the experimental and theoretical studies of the solid/liquid interface and their nanocomposites became increasingly necessary. Compared to the macroscale, their physical properties might be altered considerably, for example thermal properties of solid/liquid composites. In this thesis, the thermal conductivity (TC) of solid-liquid hybrid nanocomposites is investigated, and more specifically for the dry and wet nanoporous crystalline silicon with the confined water. Several parameters have been studied in details. The thermal conductivity is calculated using Molecular Dynamics (MD) simulations, which are performed with LAMMPS. At first, a simulation cell of crystalline silicon with a spherical pore in the center is studied. The cases of dry and wet samples are compared. Using the Equilibrium Molecular Dynamics (EMD) simulations, the effects of temperature and effective density on the TC are examined, separately. I found that for certain temperature (at 300 K) or effective density (0.8 g/cm3), a surprising maximum value of TC was obtained. Furthermore, a stratification of water molecules close to the solid/liquid interface is observed confirming in the literature. To clarify the physical mechanisms behind the thermal transport at solid/liquid interfaces and the intermolecular interaction of nanoconfined water, several structural and dynamical parameters of the nanoconfined water were explored: the radial distribution function, mean square displacements, water molecules orientation, and hydrogen bond networks. Additionally, the existence of new heat flux channels between a solid matrix and a nanoconfined liquid was proved, with clear signatures in the phonon density of states. In the second part of the thesis, the effects of spatial, size and ...