Difference between revisions of "High-Order Multiple Emulsions Formed in Poly(dimethylsiloxane) Microfluidics"

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== Results and Discussion ==
 
== Results and Discussion ==
[[Image:Abate2009 1.png|600px|thumb|left|'''Fig. 1''' Ordered droplets (water and oil, alternating) formed by linear drop maker arrays. Photomicrographs of a) single, b) double, c) triple, d)quadruple, and e)quintuple emulsion drop maker arrays.The multiple emulsions produced by the arrays are shown to the right. (The scalebars are 100mm.)]]
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[[Image:Abate2009 1.png|600px|thumb|right|'''Fig. 1''' Ordered droplets (water and oil, alternating) formed by linear drop maker arrays. Photomicrographs of a) single, b) double, c) triple, d)quadruple, and e)quintuple emulsion drop maker arrays.The multiple emulsions produced by the arrays are shown to the right. (The scalebars are 100mm.)]]
[[Image:Abate2009 2.png|500px|thumb|right|'''Fig. 2''' Hexagonally packed a) single, c) double, e) triple, g) quadruple, and i) quintuple emulsions in a monolayer. The diameter distributions are shown for the b) single, d) double, f) triple, h) quadruple, and j) quintuple emulsions; the distributions for the outer drops and each of the nested inner drops are plotted individually.]]
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[[Image:Abate2009 2.png|600px|thumb|right|'''Fig. 2''' Hexagonally packed a) single, c) double, e) triple, g) quadruple, and i) quintuple emulsions in a monolayer. The diameter distributions diameter distribution (coefficient of
 +
variation (CV) of 2%) are shown for the b) single, d) double, f) triple, h) quadruple, and j) quintuple emulsions; the distributions for the outer drops and each of the nested inner drops are plotted individually.]]
  
A single emulsion of water droplets in fluorocarbon oil (w/o) is formed by injecting water at 200mL/h in the first inlet of a microtube and oil in a second inlet at 400mL/h (Fig. 1a). The single drop maker has uniform hydrophobic wettability. To form a double emulsion of o/w/o a third inlet is added to the linear drop maker where the fluid is injected at 600mL/h (Fig. 1b). By adding even more inlets and synchronizing the fluid speeds at each inlet even triple, quadruple and quintuple emulsion were formed (Fig. 1c-e).
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Microfluidic drop formation of monodisperse emulsions in monolayers were combined with the scalability of lithographically fabricated devices. A single emulsion of water droplets in fluorocarbon oil (w/o) is formed by injecting water at 200mL/h in the first inlet of a microtube and oil in a second inlet at 400mL/h (Fig. 1a). The single drop maker has uniform hydrophobic wettability. To form a double emulsion of o/w/o droplets a third inlet is added to the linear drop maker where the fluid is injected at 600mL/h (Fig. 1b). By adding even more inlets and synchronizing the fluid speeds at each inlet even triple, quadruple and quintuple emulsion were formed (Fig. 1c-e). Droplets are confined in between two plates that are 50 <math>\mu m</math> apart to guarantee a monolayer formation.
  
In that way monodisperse higher order emulsion can be formed. Since the microcapillary devices fabrication is very difficult the scalability of the emulsification process is restricted. Linear arrays of poly(dimethylsiloxane) (PDMS) drop makers with alternating wettability were fabricated such that drops form from each channel. The nozzle is desgined such that it is slightly narrower than the incoming emulsion from the previous drop maker: "This allows the incoming emulsion to obstruct the nozzle, perturbing flow, and triggering the formation of the outer drop."
+
Linear arrays of poly(dimethylsiloxane) (PDMS) drop makers with alternating wettability were fabricated such that drops form from each channel. The nozzle is desgined such that it is slightly narrower than the incoming emulsion from the previous drop maker: "This allows the incoming emulsion to obstruct the nozzle, perturbing flow, and triggering the formation of the outer drop."
  
A superior method would combine the control of
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In that way monodisperse higher order emulsion can be formed, which all pack hexagonally. Since the microcapillary devices fabrication is very difficult the scalability of the emulsification process is still restricted.  
microfluidic drop formation with increased scalability.
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Devices in PDMS were coated with a photoreactive sol-gel mixture which provides hydrophilic channels where exposed with UV light and hydrophobic channel parts where not exposed. In that way the devices were fabricated using softlithography. Hydrophilic channels are suited to form oil-in-water emulsions.
method here combines the control of microfluidic drop formation with the scalability of lithographically fabricated devices.[10] We use
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+
 
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Weconfine our
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drops in a monolayer by sandwiching them between two plates
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that are 50mmapart.
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diameter distribution is narrow, with coefficient of
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variation (CV) of 2%,
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Similarly, the
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triple, quadruple, and quintuple emulsions all pack hexagonally
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because all are monodisperse
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The emulsions pack hexagonally because they
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areconfinedinamonolayerandmonodisperse.
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Experimental Section
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Preparation of devices: The devices are fabricated using softlithography
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in PDMS. [10] All devices are fabricated at a fixed
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channel height of 50 mm. The PDMS devices are bonded to a glass
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plate using oxygen-plasma treatment To spatially control wettability,
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the devices are coated with a photoreactive sol–gel
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[11]
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within 15 minutes after plasma bonding. The devices are filled
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with the photoreactive sol–gel mixture and heated with a hotplate
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set to 225 8C; this vaporizes the solvent in the mixture and
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deposits the coating. The coating makes the channels hydrophobic
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by default; to spatially pattern wettability, we graft patches
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of hydrophilic polyacrylic acid onto the interface using utraviolet
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(UV) light-initiated polymerization. To accomplish this we fill the
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coated channels with the hydrophilic monomer solution and
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expose them to spatially patterned UV light. When exposed to
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light, the photoinitiator silanes embedded in the sol–gel release
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radicals that initiate polymerization of the acrylic acid monomers
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in solution. The resulting acrylic acid polymers are grafted to the
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sol–gel interface, tethered by covalent linkages with the photoinitiator
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silanes. This results in a dense covering of polyacrylic
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acid of the interface, making it very hydrophilic, suitable for
+
forming oil-in-water emulsions.
+

Latest revision as of 23:47, 20 September 2010

Birgit Hausmann
Abate2009 4.jpg

Reference

A. R. Abate and D. A. Weitz "High-Order Multiple Emulsions Formed in Poly(dimethylsiloxane) Microfluidics" Small 5(18), 2030-2032 (2009)

Keywords

microfluidics, multiple emulsions, photoresponsive materials, sol–gel processes, wettability

Overview

Droplets encapsulated multiple times in droplets of alternating kinds of fluids (oil, water) were emulsified in a highly controlled way. PDMS microcapillary devices were used to guarantee monodispersity of higher order emulsions, at the expense of large quantity formation.

Results and Discussion

Fig. 1 Ordered droplets (water and oil, alternating) formed by linear drop maker arrays. Photomicrographs of a) single, b) double, c) triple, d)quadruple, and e)quintuple emulsion drop maker arrays.The multiple emulsions produced by the arrays are shown to the right. (The scalebars are 100mm.)
Fig. 2 Hexagonally packed a) single, c) double, e) triple, g) quadruple, and i) quintuple emulsions in a monolayer. The diameter distributions diameter distribution (coefficient of variation (CV) of 2%) are shown for the b) single, d) double, f) triple, h) quadruple, and j) quintuple emulsions; the distributions for the outer drops and each of the nested inner drops are plotted individually.

Microfluidic drop formation of monodisperse emulsions in monolayers were combined with the scalability of lithographically fabricated devices. A single emulsion of water droplets in fluorocarbon oil (w/o) is formed by injecting water at 200mL/h in the first inlet of a microtube and oil in a second inlet at 400mL/h (Fig. 1a). The single drop maker has uniform hydrophobic wettability. To form a double emulsion of o/w/o droplets a third inlet is added to the linear drop maker where the fluid is injected at 600mL/h (Fig. 1b). By adding even more inlets and synchronizing the fluid speeds at each inlet even triple, quadruple and quintuple emulsion were formed (Fig. 1c-e). Droplets are confined in between two plates that are 50 <math>\mu m</math> apart to guarantee a monolayer formation.

Linear arrays of poly(dimethylsiloxane) (PDMS) drop makers with alternating wettability were fabricated such that drops form from each channel. The nozzle is desgined such that it is slightly narrower than the incoming emulsion from the previous drop maker: "This allows the incoming emulsion to obstruct the nozzle, perturbing flow, and triggering the formation of the outer drop."

In that way monodisperse higher order emulsion can be formed, which all pack hexagonally. Since the microcapillary devices fabrication is very difficult the scalability of the emulsification process is still restricted. Devices in PDMS were coated with a photoreactive sol-gel mixture which provides hydrophilic channels where exposed with UV light and hydrophobic channel parts where not exposed. In that way the devices were fabricated using softlithography. Hydrophilic channels are suited to form oil-in-water emulsions.