  Diffusiophoresis, a ubiquitous phenomenon that induces particle transport
whenever solute concentration gradients are present, was recently observed in
the context of microsystems and shown to strongly impact colloidal transport
(patterning and mixing) at such scales. In the present work, we show
experimentally that this nanoscale mechanism can induce changes in the
macroscale mixing of colloids by chaotic advection. Rather than the decay of
the standard deviation of concentration, which is a global parameter commonly
employed in studies of mixing, we instead use multiscale tools adapted from
studies of chaotic flows or intermittent turbulent mixing: concentration
spectra and second and fourth moments of the probability density functions of
scalar gradients. Not only can these tools be used in open flows, but they also
allow for scale-by-scale analysis. Strikingly, diffusiophoresis is shown to
affect all scales, although more particularly the small ones, resulting in a
change of scalar intermittency and in an unusual scale bridging spanning more
than seven orders of magnitude. By quantifying the averaged impact of
diffusiophoresis on the macroscale mixing, we explain why the effects observed
are consistent with the introduction of an effective P\'eclet number.
