Mechanics in Biology & Fluids
Slip at the Interface Between a Liquid and a Solid

It has been noted that the mean velocity of the liquid molecules adjacent to a solid have a non-zero velocity – that is, they slip-relative to the solid. But, what is the manner in which liquids move over a solid? Do all of the liquid molecules slowly drift over the solid surface? Or, are the liquid molecules mostly stationary, and only a few molecules zip across the solid surface? We have shown that both types of slip can occur. We find the latter type most interesting, for the molecules zipping across the interface do so as solitons, and so slip can be described analytically in terms of a collection of localized disturbances.

Figure 1

In Figure 1, molecular trajectories predicted by a simple analytical model (left column) are compared with numerical computations (right column). The purple ovals show the trajectory of a soliton propagating across the liquid-solid interface (Phys. Rev. Lett. 93: 086001 - 2004).