  When a mixture of two viscous liquids flows past a solid wall there is an
ambiguity in the use of the no-slip boundary condition. It is not obvious
whether the mass-averaged velocity, the volume-averaged velocity, the
individual species velocities, all or none of the above, or none of the above
should exhibit no-slip. Extensive molecular dynamics simulations of the
Poiseuille flow of mixtures of coexisting liquid species past an atomistic wall
indicate that the velocity of each individual liquid species satisfies the
no-slip condition and, therefore, so do mass and volume averages.
