The Molecular Origin of Slip*

Liquid flow adjacent to a solid surface can slip resulting in a finite liquid velocity at the solid/liquid interface. However, how this liquid slip occurs is poorly understood. Here, we study liquid films driven over a solid surface. We show that slip over the surface is not simply the result of independent molecular hops over the solid substrate. Rather, much of the velocity at the solid/liquid interface results from correlated motion of several molecules which propagate as nonlinear waves similar to solitons. Solitons are fundamentally important in the fluid mechanics of slip. Understanding their dynamics may suggest new methods of designing low drag surfaces and new technologies for chemical separations.