Transcript Laura Schmidt, PHY335, Dec. 2, 2003 Selective withdrawal

Laura Schmidt, PHY335, Dec. 2, 2003
Selective 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 nonNewtonian fluids.
Newtonian fluids vs. non-Newtonian fluids
Newtonian fluids follow Newton’s law of viscosity:
the shear stress is proportional to the rate of shear
strain, with the constant of proportionality defined as
the viscosity, η.
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.
Selective withdrawal is used to coat microparticles
The selective withdrawal process is one of
the most viable means of coating microparticles, 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
The experimental set-up
pump
waste
pipette
oil
camera
solution
8 cm
Polyethylene glycol diacrylate
Q
The transition’s 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.
Q