Kerstin Nordstrom
Clare Boothe Luce Assistant Professor of Physics, Mount Holyoke College
PhD, University of Pennsylvania, 2010
MS, University of Pennsylvania, 2006
BA, Bryn Mawr College, 2004
Current research interests: microfluidics, colloids,
biophysics, rheology of complex fluids
Faculty Collaborators: Jerry Gollub*, Paulo Arratia, Paul
Janmey, Arjun Yodh
*co-advisor
Complex fluids possess structure on a mesoscopic length
scale between the molecular scale and the macroscopic
scale. Examples include foams, colloidal suspensions,
polymer solutions, emulsions, etc. While the macroscopic
and molecular scales may be well understood, fluids may
have complex properties solely due to underlying mesoscopic
structure. Think about a bottle of soapy water with a layer
of air at the top. The molecular properties are
established: the water is well understood, the air is well
understood. The macroscopic properties are established: the
relative percentages of water, soap, and air. However, a
shaken bottle will have much different behavior than an
unshaken bottle, simply due to the presence of the
mesoscopic foam bubbles.
Microfluidics offers unique opportunities for studying
various phenomena such as complex fluid flow. Most
importantly, since microfluidic channels are small, flows
are kept to low Reynolds number, making flows laminar (not
turbulent) and easier to interpret. The device size also
makes microscopy a valuable tool for studying flows, in
other words, we can directly see the microstructure of the
flows of interest. In a complex fluid, one may expect
confinement effects to become important as the channel size
approaches the size of the mesoscale structure. Indeed this
can be the case, and is an additional important area of
inquiry in microfluidics, especially from a practical
standpoint as microfluidic devices become more common in
clinical settings.
Microfluidic Rheology of
Microgel Pastes
with Emilie Verneuil
The complex fluid we study is a dense suspension, a “paste”
of NIPA particles. NIPA particles are tiny gel particles,
about 1 um in diameter, suspended in water. We flow these
particles into a channel, and can take a video of the flow.
Using this video, we can extract strain rates. As we are
using a well-defined geometry and pressure drop, we know
the shear stresses present in our flow. Thus it is possible
to capture actual rheological data simply by looking at a
video.
One neat aspect of these particles is that they can swell
or shrink with changes in temperature. So we can change the
relative density of particles without changing the sample.
In essence, we would like to see how the flow curves
(stress vs strain rate) change as the volume fraction
changes, especially as we sweep through the jamming point.
Clogging in a Model Porous
Medium
with Emilie Verneuil and
Tim Huber
By fabricating networks of channels we create a toy model
of transport through porous media. Clogs occur at very low
particle densities. We are studying dependence of clog
formation on flow rate, particle size, volume fraction, and
surface properties.
clog
Cell Durotaxis on Gradient
Gels
with Qi Wen
It has been shown that cells migrate to stiffer substrates.
Using microfluidics, we have been able to fabricate gels
with controlled stiffness gradients. Quantitative cell
studies are underway in the Janmey group.