Colloidal
Interactions
The forces between colloidal particles play a crucial role in
determining the structure and stability of suspensions, and therefore
their response to optical, mechanical and electromagnetic
stimuli. We're developing new ways to measure and
manipulate these forces. In nonpolar environments, we're
exploring
methods to control electrostatic forces. In aqueous
environments,
we're exploiting the properties of biological molecules to create novel
interactions
|
 |
|
|
Micro-Opto-Mechanical Systems
(MOMS)
We manipulate individual colloidal particles using optical
forces. An single optical tweezer can trap a micron-sized
particle near the focal point of a laser beam. We have
developed
holographic methods to manipulate hundreds of particles
simultaneously. Each particle can be independently and
dynamically moved in 3D. We're developing new applications
for
this powerful tool in the physical and biological sciences.
|
|
|
|
Complex Fluids in Microchannels
Suspensions may flow through microchannels very
differently than they do through macroscale devices. For example,
the effective viscosity of blood in the microcirculation may be less
than half the bulk viscosity. Indeed, micro-scale flow may
be non-Newtonian in regimes where bulk rheology is linear and
Newtonian. Mechanisms such as geometric confinement, Brownian
motion, particle/particle interactions and particle/wall
interactions can all play important roles. We are interested in
understanding the behavior of both model hard- and soft-sphere systems
as well as real biological suspensions. Using both high-speed and
confocal microscopy, we investigate the flow of these suspensions
through microfluidic channels. We reconstruct the flow in 3D to
analyze its structure and dynamics. More...,
|
 |
|
|
|
Plasmonics
Nanoscale metallic structures exhibit
suprising
optical phenomena. By coupling photons to surface
resonanances
(surface plasmon-polaritons), metallic nanowires can guide
and
redirect light can over tens of microns. We are
investigating
the fundamental physics of this phenomenon and exploring potential
applications to integrated nanophotonic devices. |
 |
|
|
Mechanics of Drying Suspensions
Drying suspensions can fracture and buckle like elastic solids - even
when the concentration of solid particles is vanishingly small. The
basic physics of these instabilities are relatively well-understood for
elastic materials. However, drying suspensions can be viscoelastic:
depending on the experimental timescale, they can either store energy
in elastic deformation or relieve stress through viscous flow. In
addition, the kinetics of drying drives suspensions far from
equilibrium, leading to dramatic changes in material properties as
solvent evaporates. We're trying to understand the interplay
of
forces, structure and kinetics that causes colloidal fluids to jam,
buckle and crack. We're exploring applications to spray-dried
powders, coatings and ceramics.
|
 |
Research Supported by:
|
|
    
|
|
|
