| dc.description.abstract | Macroscopically, liquid °ows smoothly under external shears. Neverthe-
less, the physical picture of a sheared liquid beyond the continuous limit
remains elusive. The studies of micro-motions and structures in a sheared
liquid have been mainly limited to the macroscopic force and the velocity
measurement on the con¯ning boundary because of the lack of microscopic
measures at the small scale, which is insu±cient to provide an obvious mi-
croscopic picture at the discrete molecular level.
A dusty plasma liquid (DPL) formed by micrometer sized dust particles
negatively charged and suspended in a low-pressure weakly ionized discharge
background is an inspiring system to mimic and understand the generic dy-
namical behaviors of a liquid in nature at the kinetic level because of the
capability of directly visualization. Vertically, the suspended dust particles
are aligned through the wake-¯eld e®ect of the downward ion °ow. Thus,
these particles cannot hop vertically. When the number of particles in each
chain is less than 10, particles in the same chain move together horizontally.
Consequently, it can be regarded as a quasi-2D system. In this work, us-
ing a con¯ned mesoscopic quasi-2D DPL sheared by two counter steadily
or periodic chopped laser beams along the opposite boundaries, we investi-
gate the shear banding and thinning, and explore the physical origins of the
visco-elastic response of a thin liquid through correlating the micro-structural
evolution and displacements using a novel correlation probability method.
We demonstrate the shear banding and the enhanced avalanche-type lo-
cal topological transitions with stress relaxation in the form of clusters in
steadily sheared mesoscopic dusty plasma liquids. The frequently avalanche-
type structural rearrangements exhibiting in the outer sheared zone dissipate
i
the external stress and screen the momentum cascaded into the center. It
leaves two outer thin regions a few inter-particle distance in width with high
shear rate sandwiching a plug-like central region with low shear rate. When
we use the periodic moderated shear-pulse instead of a constant stress, the
visco-elastic response is observed. The relations of the elastic (reversible)
and viscous (irreversible) responses and the topological structural memory
are further identi¯ed by correlating the micro-structural evolutions and dis-
placements in the laser-on and -o® durations. The plastic deformation is
generated by bond breaking, kinking, and reconnection through hopping.
The strain energy accumulation in the twisted regions without topological
rearrangement is the source for local rebound. The reorganized structure ex-
hibits di®erent spatiotemporal response in the next stress-on and -o® cycle.
In addition, increasing the number of particles, we can turn the quasi-2D
DPL into the ’’2+1’’D DPL which is composed the bundles of long vertical
particle chains. A digital stereo video particle imaging system is constructed
to directly track the trajectories of particles in the xy planes at di®erent
heights. We present the micro-motions of the ’’2+1’’D DPL at the di®erent
heights, identify its basic excitations. The preliminary observation of the
dynamical behaviors of the entanglement, breaking and reconnection are also
investigated and discussed in this thesis. | en_US |