  We propose a novel strategy for designing chaotic micromixers using curved
channels confined between two flat planes. The location of the separatrix
between the Dean vortices, induced by centrifugal force, is dependent on the
location of the maxima of axial velocity. An asymmetry in the axial velocity
profile can change the location of the separatrix. This is achieved physically
by introducing slip alternatingly at the top and bottom walls. This leads to
streamline crossing and Lagrangian chaos. An approximate analytical solution of
the velocity field is obtained using perturbation theory. This is used to find
the Lagrangian trajectories of fluid particles. Poincare sections taken at
periodic locations in the axial direction are used to study the extent of
chaos. The extent of mixing, for low slip and low Reynolds numbers, is shown to
be greater when Dean vortices in adjacent half cells are counter-rotating. Wide
channels are observed to have much better mixing than tall channels; an
important observation not made for separatrix flows till now. Eulerian
indicators are used to gauge the extent of mixing with varying slip length and
it is shown that an optimum slip length exists which maximizes the mixing in a
particular geometry.
