Stability of Flowing NonNewtonian Liquids of Cylindrical Shape

1
Stability of Flowing Non-Newtonian Liquids of
Cylindrical Shape

• Kazem Edmond, A.D. Dinsmore,
• Department of Physics, U. Mass., Amherst
• J.P. Rothstein,
• Department of Mechanical and Industrial
  Engineering, U. Mass., Amherst
• Manuel Marquez
• Kraft Foods, Inc. and Los Alamos National
  Laboratories

2
Motivation

• Ultimate Goal Develop a method for the
  self-assembly of rigid cylinders.
• Coat cylindrical fluid interfaces with
  nano-spheres.

3
Motivation Continued

• Develop a consistent method for the creation of
  long-lived coherent jets.
• Build a device that produces cylindrically shaped
  fluid interfaces via flowing streams of water and
  oil.

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Outline

• Motivation
• Part 1 Jetting
• History and Previous Work
• Design of Apparatus
• Results
• Part 2 Encapsulation
• History
• Results (Self-Assembled Cylinders)
• Conclusion

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Spheres are easy

• Droplets of water suspended in oil normally form
  spheres, and not cylinders.
• But we need a cylindrical fluid interface

A sphere maximizes volume, while minimizing
surface area, resulting in the least amount of
surface tension. Less surface tension requires a
lower amount of free surface energy.
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but cylinders are hard.

• While we cannot force droplets to be cylindrical,
  jets of water are naturally cylindrical.
• To produce jets
• Overcome the Rayleigh Instability, which is
  responsible for droplet formation.
• Use a coaxial hydro-dynamic flow-focusing
  geometry.

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Related Work

• Previous experiments have demonstrated a
  controlled method of droplet production (oil and
  water).
• Jetting was observed at high oil-flow velocities.
• We will use a non-Newtonian inner fluid.
• A polymer (polyacrylamide) dissolved in water
  will help maintain a longer lasting coherent jet,
  giving enough time for particle adsorption.

S.L. Anna, N. Bontoux, H.A. Stone, Appl. Phys.
Lett. 82, Number 3, 20 Jan. 2003.
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Polyacrylamide

• Polyacrylamide is a long polymer. MW (5-6)x106
• The polymer acts as a non-linear entropic spring.
• Stretches, resists extensional flow (very high
  extensional viscosity).
• Exerts normal stress on the oil-water
  interface--counters the Laplace pressure.
• The waters viscosity changes with shear-rate.

Elongated Entropic spring
Random Coil
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Design
OIL
WATER
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Apparatus

• Producing long-lived coherent jets using a
  flow-focusing geometry.
• Oil flows around an inner stream of water.

Water
Oil
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Jetting in Action
100 mm
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Controllable Jets
100 mm
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Data
JETTING
80 mm
50 mm
30 mm
DROPLETS
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Jet Encapsulation

• We want to coat our stable jets with nano-spheres.

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Encapsulation

• Shells formed with spherical droplets
• A.D. Dinsmore, et al., Science 298, 1006 (2002)
• Y. Lin, et al., Science 299, 226 (2003)

A Scanning electron microscope of a dried
10-µm-diameter colloidosome composed of 0.9-
µm-diameter polystyrene spheres.
A 0.7- µm-diameter PMMA spheres adsorbed onto
surface of water droplet. B Single-layer-thick
image of PMMA particles.
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Spheres
20 mm
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Cylinders
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More Cylinders
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Conclusion

• Cylindrical fluid interfaces were achieved using
  a coaxial flow arrangement.
• Interface is stable long enough for adsorption to
  take place.
• Plans for the Future
• Make more and better cylinders.
• Dynamics of the Assembly.
• Mechanical Properties of the Cylinders.