Rob R. Graham

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Production of Co-Polymer Particles in
Microfluidic Devices

• Rob R. Graham
• Patrick C. Lewis
• Eugenia Kumacheva

Lash Miller Chemical LaboratoriesToronto, ON
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Schematic of a Microfluidic Chip
Material of the mould can be either Polyurethane
(PU) or poly(dimethyl siloxane) (PDMS). PU is
relatively hydrophilic with a contact angle of
ca. 80, compared to PDMS with 108 3.
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Materials Methods
Acrylic Acid
Tripropylene glycol diacrylate (TPGDA)
TPGDA AA mixture with 5 AA particles. The scale
bar is 100µm. Droplets were photopolymerized in
situ using a polyurethane Microfluidic flow
focusing device (MFFD)
Schematic from 1
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What are potential applications?

• Quick an easy way to prepare 10-100µm polymer
  particles, a size regime usually inaccessible to
  conventional polymerization.
• Particles have extremely high monodispersity
  measured by the coefficient of variation.
• Microbeads can be used for detection and
  separation of biomolecules.
• Particles can be easily doped with quantum dots
  or magnetic nanoparticles.

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Tuning Droplet Size
Significant droplet size decrease upon adding a
more hydrophilic monomer
The ratio between the outer channel flow rate to
the inner channel flow rate is called the flow
rate ratio. This is usually greater than 50.
Figure courtesy of Patrick Lewis
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Interfacial Tension
v is fluid velocity, ? is viscosity, and ? is the
interfacial tension between the monomer and the
continuous phase. The capillary number can be
used to explain trends, but not to calculate
absolute values.
Pure TPGDA has viscosity of 13cP. 5 and 8AA
have viscosities of 12.6 and 12.2cP resp. Only 6
reduction from original.
8AA has interfacial energy that is 15 less than
pure TPGDA
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Size of Droplets
Right 8 AA in TPGDA. Droplets are 75 µm. The
flow rate ratio is 501
A Main goal of the project is to miniaturize
droplets to make ca. 10 micron particles via UV
polymerization One approach is to decrease the
interfacial tension, which allows for smaller
droplets to form.
Left 20 AA in TPGDA. The Interfacial tension is
too low for the stream to be emulsified.
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Size of Droplets
TPGDA droplets, Orifice cross sectional area 75
x 60 µm Droplet size is ca. 75 µm
Scale bars are 75 µm
TPGDA droplets, Orifice cross sectional area 15
x 41 µm Droplet size is ca. 40 µm
TPGDA droplets, Orifice cross sectional area 25
x 20 µm Droplet size is ca. 14 µm
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Phase Inversion
In general the liquid that most likes to wet the
mould will form the continuous phase past the
orifice 2.
(a,c) moap-dms in outer channel, 2 wt. SDS
solution in inner channel. (b,d) 2 wt. SDS
solution in outer channel, moap-dms in inner
channel.
Scale bar is 200µm moap-DMS is methacryloxypropyl
terminated dimethylsiloxane
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Emulsification of TPGDA
PU
PDMS
Moderately hydrophobic monomers like TPGDA can be
emulsified using either PU or PDMS for the MFFD
Scale bar 75 microns
The flow rate ratio was 1001
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Emulsification of a Hydrophobic Monomer at low
Flow Rates
The extremely hydrophobic monomer sticks to PDMS
much more than PU
1H, 1H- heptafluorobutyl methacrylate
The Flow Rate Ratio was 101 Scale bar is 75
microns
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Conclusions

• Both viscosity and interfacial tension are
  responsible for the decrease in size observed for
  droplets of monomer mixtures.
• The affinity of monomers to the MFFD is critical
  in determining if the emulsion will be direct or
  inverse.
• Both PU and PDMS can be used to emulsify
  moderately hydrophobic monomers.
• Miniaturizing the orifice reduces droplet size
  significantly.

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Future Work
Copolymerize TPGDA with primary amine containing
monomers. Continue to miniaturize dimensions in
MFFDs to make even smaller droplets. Test
emulsion conditions using sandwich MFFDs where
glass is replaced with mould material.
Aminoethyl methacrylate
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Selected References
1. Duffy, D. C., Anal Chem,1998, 70, 4974 2.
Umbanhowar, P. B., Prasad, V., Weitz, D. A.,
Langmuir, 2000, 16, 347 3. Lee, J. N., Park, C.,
Whitesides, G. M., Anal. Chem., 2003, 75, 6544
Acknowledgements
I would like to thank the entire Kumacheva group
for a fantastic research and learning
experience. I would also like to gratefully
acknowledge the U of T Department of Chemistry,
the University of Toronto, and everyone who made
SOUSCC 2005 happen.