Motion of grains, droplets, and bubbles in fluid-filled nanopores.

Molecular dynamics studies of nanometer-sized rigid grains, droplets and bubbles in nanometer-sized pores indicate that the drag force may have a hydrodynamic form if the moving object is dense and small compared to the pore diameter. Otherwise, the behavior is nonhydrodynamic. The terminal speed is insensitive to whether the falling droplet is made of liquid or a solid. The velocity profiles within droplets and bubbles that move in the pore are usually nonparabolic and distinct from those corresponding to individual fluids. The density profiles indicate motional shape distortion of the moving objects.