Molecular dynamics study for channel size dependence of shear stress between droplet and wall

In this study, the channel size dependence of the shear stress between water droplets and solid walls in nm-order channel was analyzed. We considered a several different-sized and highly hydrophobic channel whose macroscopic contact angle was about 150 degrees. We have evaluated the shear stress and the normal pressure by molecular dynamics simulation. Analyzing shear stress and normal pressure based on the macroscopic model, we have discussed the difference between the macroscopic model based on hydrodynamics and the microscopic model. As a result, in the high hydrophobic case, it became clear that the shear stress depends on the channel size due to the large Laplace pressure. Furthermore, in the case that the channel size was less than 50 A˚, the normal pressure by the molecular simulation didn't agree with the expected value from the Young-Laplace equation. From this study it was clear that molecular simulation is needed when the channel size is less than 40 A˚.