Laura Schmidt, PHY335, Dec' 2, 2003 Selective withdrawal using nonNewtonian fluids

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Laura Schmidt, PHY335, Dec. 2, 2003Selective
withdrawal using non-Newtonian fluids
The process withdrawing fluid through a pipette
positioned above a two-fluid interface. Much
work has already been done to characterize the
interface profiles for Newtonian, but not
non-Newtonian fluids.
Newtonian fluids vs. non-Newtonian
fluids Newtonian fluids follow Newtons law of
viscosity the shear stress is proportional to
the rate of shear strain, with the constant of
proportionality defined as the viscosity, ?.
Newtonian water, oil, glycerol.
non-Newtonian gels, pastes, polymer solutions
I. Cohen, Scaling dependence on the fluid
viscosity ratio in the selective withdrawal
transition, 2001.
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Selective withdrawal is used to coat
microparticles
The selective withdrawal process is one of the
most viable means of coating micro-particles,
crucial in -immobilized catalytic chemical
processes -cell and tissue encapsulation and
-local drug delivery.
I. Cohen et al., Science 292 (2001), 265-267.
Selective withdrawal is preferred over other cell
coating techniques because it can produce uniform
coats on different sized cells and has fewer
restrictions on chemical composition.
0.5 mm
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The experimental set-up
Polyethylene glycol diacrylate
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The transitions dependence on the system
parameters
A series of experiments will be performed to
determine how the transition (from hump to spout
profile) depends on the withdrawal rate (Q) and
the height of the pipette above the interface
(S). The profiles are recorded by a video camera
and then transferred to a computer, where an
already existing edge-tracing program tracks and
records the profile.
For example Vary S and hold Q fixed (for a range
of values). Record at transition - Su, the
transition tube height - k, the radius of
curvature of the hump tip - h, the height of the
hump Then, the dependence on Q of Su, k, and h
can be seen and compared to the Newtonian fluid
cases.