  Extreme deformation of soft matter is central to our understanding of the
effects of shock, fracture, and phase change in a variety of systems. Yet,
despite, the increasing interest in this area, far-from-equilibrium behaviours
of soft matter remain challenging to probe. Colloidal suspensions are often
used to visualise emergent behaviours in soft matter, as they offer precise
control of interparticle interactions, and ease of visualisation by optical
microscopy. However, previous studies have been limited to deformations that
are orders of magnitude too slow to be representative of extreme deformation.
Here we use a two-dimensional model system, a monolayer of colloids confined at
a fluid interface, to probe and visualise the evolution of the microstructure
during high-rate deformation driven by ultrasound. We observe the emergence of
a transient network of strings, and use discrete particle simulations to show
that it is caused by a delicate interplay of dynamic capillarity and
hydrodynamic interactions between particles oscillating at high-frequency.
Remarkably, we find evidence of inertial effects in a colloidal system, caused
by accelerations approaching 10,000g. These results also suggest that extreme
deformation of soft matter offers new opportunities for pattern formation and
dynamic self-assembly.
