Capillary forces are dominant in adhesive forces measured with an atomic force microscope (AFM) in ambient air, which are thought to be dependent on water film thickness, relative humidity and the free energy of the water film. In this paper, besides these factors, we study the nature of the 'pull-off' force on a variety of atmospheres as a function of the contact time. It is found that capillary forces strongly depend on the contact time. In lower relative humidity atmosphere, the adhesion force is almost independent of the contact time. However, in higher relative humidity, the adhesion force increases with the contact time. Based on the experiment and a model that we present in this paper, the growth of the liquid bridge can be seen as undergoing two processes: one is water vapour condensation; the other is the motion of the thin liquid film that is absorbed on the substrate. The experiment and the growth model presented in this paper have direct relevance to the working mechanism of AFM in ambient air.

For the first time, the enhanced recovery of confined methane (CH₄) with carbon dioxide (CO₂) is investigated through molecular dynamics simulations.

Coupling effects among lithium diffusion, stress evolution and crack propagation have a significant effect on lithium diffusion and crack propagation.

Dynamic wetting of a droplet on lyophilic pillars was explored using a multiscale combination method of experiments and molecular dynamics simulations. The excess lyophilic area not only provided excess driving force, but also pinned the liquid around the pillars, which kept the moving contact line in a dynamic balance state every period of the pillars. The flow pattern and the flow field of the droplet on the pillar-arrayed surface, influenced by the concerted effect of the liquid–solid interactions and the surface roughness, were revealed from the continuum to the atomic level. Then, the scaling analysis was carried out employing molecular kinetic theory. Controlled by the droplet size, the density of roughness and the pillar height, two extreme regimes were distinguished, i.e. $R\sim {t}^{1/ 3} $ for the rough surface and $R\sim {t}^{1/ 7} $ for the smooth surface. The scaling laws were validated by both the experiments and the simulations. Our results may help in understanding the dynamic wetting of a droplet on a pillar-arrayed lyophilic substrate and assisting the future design of pillar-arrayed lyophilic surfaces in practical applications.

The boundary slip and its mechanism were investigated using theoretical analysis and molecular dynamic simulations. We proposed a new slip boundary condition based on molecular kinetic theory, which was extended by the introduction of the critical shear stress, which determines the onset of the slip, and the energy dissipation near the liquid–solid interface at high shear stress. Our results revealed that the critical shear stress increases exponentially with the liquid–solid interactions. In particular, we discussed the energy dissipation contributed from the friction between the liquid layers near the interface. The results demonstrated that the momentum transfer among the liquid layers and the bulk liquid must be considered according to the wetting conditions of the solid surface, which can interpret the contradictory published results of slip behavior at high shear stress. The analytical expression of our slip boundary condition can be compared with the simulation results since it uses parameters consistent with that used in our molecular dynamic simulations. Furthermore, we suggested a dimensionless number to qualify the transition from Poiseuille-like to plug-like flow in the carbon nanotubes. These findings can enhance our understanding of the boundary slip.