Ce manuscrit présente une description théorique des propriétés de transport exceptionnelles des liquides dans les nanotubes de carbone (CNT). La perméabilité de ces canaux dépasse largement ce qui est prévu par les équations de l'hydrodynamique et la condition limite de non-glissement. Au cours des dernières années, plusieurs groupes ont effectué des expériences d'écoulement de liquides dans des membranes de CNT. Une perméabilité très supérieure à l'attente classique a été observée. Dans ce contexte, nous avons mené une étude exhaustive du frottement liquide/solide qui apparaît pendant l'écoulement d'un fluide dans un CNT, à l'aide de simulations de dynamique moléculaire. Le coefficient de frottement a été mesuré pour différents systèmes en utilisant plusieurs méthodes indépendantes. Les simulations ont montré que le coefficient de frottement était indépendant du confinement, mais qu'il dépendait considérablement de la courbure de la paroi. Pour l'eau dans un CNT, le coefficient de frottement diminue avec le rayon du tube. Nous avons ensuite établi une expression approchée du coefficient de frottement, qui le relie à des propriétés microscopiques de l'interface entre le liquide et la paroi. Cette expression reproduit la dépendance du coefficient de frottement avec la courbure, et permet de l'expliquer à partir des trois paramètres statiques suivants : la densité surfacique de l'eau, la rugosité de la paroi et la commensurabilité entre les structures de la paroi et de la première couche d'eau à l'interface. En résumé, notre étude a permis une compréhension détaillée du frottement de l'eau dans les CNT, qui explique l'origine de sa valeur extrêmement basse. / Within the scope of this thesis, a theoretical study of liquid flow in graphitic nanopores was performed. More precisely, a combination of numerical simulations and analytic approach was used to establish the special properties of carbon nanotubes for fluid transport: Molecular dynamics flow simulations of different liquids in carbon nanotubes exhibited flow velocities that are 1-3 orders of magnitude higher than predicted from the continuum hydrodynamics framework and the no-slip boundary condition. These results support previous experiments performed by several groups reporting exceptionally high flow rates for water in carbon nanotube membranes. The reason for this important flow enhancement with respect to the expectation was so far unclear. In this work, a careful investigation of the water/graphite friction coefficient which we identified as the crucial parameter for fast liquid transport in the considered systems was carried out. In simulations, the friction coefficient was found to be very sensitive to wall curvature: friction is independent of confinement for water between at graphene walls with zero curvature, while it increases with increasing negative curvature (water at the outside of the tube), and it decreases with increasing positive curvature (water inside the tube), eventually leading to quasi frictionless flow for water in a single file configuration in the smallest tubes. A similar behaviour was moreover found with several other liquids, such as alcohol, alcane and OMCTS. urthermore, a theoretical approximate expression for the friction coefficient is presented which predicts qualitatively and semi-quantitatively its curvature dependent behavior. Moreover, a deeper analysis of the simulations according to the proposed theoretical description shed light on the physical mechanisms at the origin of the ultra low liquid/solid friction in carbon nanotubes. In fine, it is due to their perfectly ordered molecular structure and their atomically smooth surface that carbon nanotubes are quasi-perfect liquid conductors compared to other membrane pores like, for example, nanochannels in amorphous silica. The newly gained understanding constitutes an important validation that carbon nanotubes operate as fast transporters of various liquids which makes them a promising option for different applications like energy conversion or filtration on the molecular level.

Within the scope of this thesis, a theoretical study of liquid flow in graphitic nanopores was performed. More precisely, a combination of numerical simulations and analytic approach was used to establish the special properties of carbon nanotubes for fluid transport: Molecular dynamics flow simulations of different liquids in carbon nanotubes exhibited flow velocities that are 1-3 orders of magnitude higher than predicted from the continuum hydrodynamics framework and the no-slip boundary condition. These results support previous experiments performed by several groups reporting exceptionally high flow rates for water in carbon nanotube membranes. The reason for this important flow enhancement with respect to the expectation was so far unclear. In this work, a careful investigation of the water/graphite friction coefficient which we identified as the crucial parameter for fast liquid transport in the considered systems, was carried out. In simulations, the friction coefficient was found to be very sensitive to wall curvature: friction is independent of confinement for water between flat graphene walls with zero curvature, while it increases with increasing negative curvature (water at the outside of the tube), and it decreases with increasing positive curvature (water inside the tube), eventually leading to quasi frictionless flow for water in a single file configuration in the smallest tubes. A similar behavior was moreover found with several other liquids, such as alcohol, alcane and OMCTS. Furthermore, a theoretical approximate expression for the friction coefficient is presented which predicts qualitatively and semi-quantitatively its curvature dependent behavior. Moreover, a deeper analysis of the simulations according to the proposed theoretical description shed light on the physical mechanisms at the origin of the ultra low liquid/solid friction in carbon nanotubes. In fine, it is due to their perfectly ordered molecular structure and their atomically smooth surface that carbon nanotubes are quasi-perfect liquid conductors compared to other membrane pores like, for example, nanochannels in amorphous silica. The newly gained understanding constitutes an important validation that carbon nanotubes operate as fast transporters of various liquids which makes them a promising option for different applications like energy conversion or filtration on the molecular level.