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A microfluidic cross-flowing emulsion generator for producing biphasic droplets and anisotropically shaped polymer particles

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Abstract

We present a microfluidic cross-flowing system for producing biphasic emulsion droplets and non-spherical polymer microparticles. Microfluidic channels on a glass chip comprise a Y-shaped channel so as to form a two-phase organic stream of photocurable and non-curable phases, and a T-junction to generate phase-separated droplets in a cross-flowing aqueous stream. The biphasic droplets at equilibrium formed a Janus configuration (partial engulfing) or a core–shell configuration (complete engulfing) consistent with minimizing the interfacial free energies among the three liquid phases, according to the three spreading coefficients. When silicone oil was used as the non-curable phase, monodisperse Janus droplets were generated reproducibly in a one-step process; for e.g., the mean particle size was 119 μm with a coefficient of variation (CV) of 1.9%. Subsequent UV-initiated polymerization yielded monodisperse particles with controlled convex/concave structures, which were tunable through variation of the ratio of the flow rates between the two organic phases. In contrast, when perfluorocarbon fluid, which is more hydrophobic than silicone oil, was used as the non-curable phase, monodisperse core–shell droplets were generated in a two-step regime, leading to the synthesis of cross-linked polymeric shells with a pore on their surfaces. We also investigated how the asymmetric flow configuration influenced droplet formation at the T-junction.

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Abbreviations

2D:

Two dimensional

3D:

Three dimensional

Ca :

Capillary number

CV:

Coefficient of variation

D h :

Hydraulic diameter

DRIE:

Deep reactive ion etching

f b :

Rate of droplet breakup

HDDA:

1,6-hexanediol diacrylate

M w :

Molecular weight

PFC:

Perfluorocarbon fluid

PTFE:

Poly(tetrafluoroethylene)

PVA:

Polyvinyl alcohol

Q c :

Volumetric flow rate of the continuous phase

Q d :

Total volumetric flow rate of the photocurable and non-curable phases

Q m :

Volumetric flow rate of the photocurable monomer (HDDA)

Q p :

Volumetric flow rate of the perfluorocarbon fluid

Q s :

Volumetric flow rate of the silicone oil

SDS:

Sodium dodecyl sulfate

SEM:

Scanning electron microscopy

S i :

Spreading parameter

UV:

Ultraviolet

v :

Flow velocity

wt%:

Weight percent

γ :

Interfacial tension or surface tension

γ 12 :

Interfacial tension at the interface 12

γ 23 :

Interfacial tension at the interface 23

γ 31 :

Interfacial tension at the interface 31

η :

Fluid viscosity

η m :

Viscosity of the photocurable monomer (HDDA)

η s :

Viscosity of the silicone oil

η p :

Viscosity of the perfluorocarbon fluid

ρ m :

Density of the photocurable monomer (HDDA)

ρ s :

Density of the silicone oil

ρ p :

Density of the perfluorocarbon fluid

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Acknowledgments

TN gratefully acknowledges the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) in Japan (Grant-in-Aid for Young Scientists (B) No. 19710114 and No. 21710124), Hosokawa Particle Technology Foundation, and Yazaki Memorial Foundation for Science & Technology for their support of this project.

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Authors and Affiliations

  1. Precision and Intelligence Laboratory, Tokyo Institute of Technology, R2-6, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan

    Takasi Nisisako & Takeshi Hatsuzawa

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  1. Takasi Nisisako
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  2. Takeshi Hatsuzawa
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Correspondence to Takasi Nisisako.

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Nisisako, T., Hatsuzawa, T. A microfluidic cross-flowing emulsion generator for producing biphasic droplets and anisotropically shaped polymer particles. Microfluid Nanofluid 9, 427–437 (2010). https://doi.org/10.1007/s10404-009-0559-6

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  • DOI: https://doi.org/10.1007/s10404-009-0559-6

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