Abstract
Shear-induced melting and crystallization were investigated by
confocal microscopy in concentrated colloidal suspensions of hardsphere-
like particles. Both silica and polymethylmethacrylate suspensions
were sheared with a constant rate in either a countertranslating
parallel plate shear cell or a counterrotating cone-plate
shear cell. These instruments make it possible to track particles
undergoing shear for extended periods of time in a plane of zero
velocity. Although on large scales, the flow profile deviated from
linearity, the crystal flowed in an aligned sliding layer structure at
low shear rates. Higher shear rates caused the crystal to shear melt,
but, contrary to expectations, the transition was not sudden.
Instead, although the overall order decreased with shear rate, this
was due to an increase in the nucleation of localized domains that
temporarily lost and regained their ordered structure. Even at
shear rates that were considered to have melted the crystal as a
whole, ordered regions kept showing up at times, giving rise to
very large fluctuations in 2D bond-orientational order parameters.
Low shear rates induced initially disordered suspensions to crystallize.
This time, the order parameter increased gradually in time
without large fluctuations, indicating that shear-induced crystallization
of hard spheres does not proceed via a nucleation and
growth mechanism. We conclude that the dynamics of melting and
crystallization under shear differ dramatically from their counterparts
in quiescent suspensions.
| Original language | Undefined/Unknown |
|---|---|
| Pages (from-to) | 10564-10569 |
| Number of pages | 6 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Volume | 106 |
| Issue number | 26 |
| Publication status | Published - 2009 |