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Oil in Water Emulsions

Oil in Water emulsions (O/W) are widely used in industrial and R&D environments to manufacture droplets (e.g., for compartmentalization applications), wax beads (e.g., carnauba or cosmetic wax), and polymer beads (e.g., PLGA, Styrene, methacrylates, etc.). Of particular importance is the ability to produce high-quality, monodisperse droplets and the ability to do so reproducibly and at a viable production rate. 

The combination of Pressure based flow controller units and Raydrop microfluidic devices enable smooth fluid delivery, precision flowrate control, automation, and reproducibility necessary to generate high-quality oil in water emulsions.

In this application note, we present droplet generation data obtained using decane in Water, a system that demonstrates the expected behavior of most hydrocarbons in Water. We demonstrate the ability of Fluigent equipment coupled with Raydrop microfluidic devices to generate high-quality emulsions with controlled droplet sizes and with high throughput.

We kindly thank of SMALL Biotechnologies for this collaboration.

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Materials and Methods

Reagents

Droplet Phase: Decane

Continuous phase: Water + 2% (wt) Sodium dodecyl sulfate (SDS)

Reagent
Supplier
Catalogue number
CAS Number
Water
Ultrapure 18.2 MΩ – cm
-
7732-18-5
Decane
Sigma Aldrich
D901
124-18-5
Sodium dodecyl sulfate
Sigma Aldrich
436143
151-21-3

Microfluidic Setup

The microfluidic setup was composed of:

2x Flow EZ (2000 mbar) pressure pumps

Microfluidic flow controller

2x Flow Units enabling flowrate control

Flow sensor

RayDrop chip

Droplet generator

 

Optical microscope

FlowUnit
RayDrop microfluidic droplet generator
Digital high-speend microscope 7092 fps

The Flow EZ is the most advanced flow controller for pressure-based fluid control. It can be combined with a Flow Unit to control pressure or flow rate. It can be used without a PC. Two Flow EZ with 2 bar of full-scale pressure are used in the setup presented here.

The Flow Unit is a flow sensor that allows real-time flow rate measurement. By combining a Flow Unit with the Flow EZ, it is possible to switch from pressure control to flow rate control, allowing for the generation of highly monodispersed droplets over a long time. Two Flow Units M are used here to monitor and control the flow rates of the dispersed and continuous phase during the run.

The RayDrop droplet and emulsion chip is used to control the generation of alginate droplet. The RayDrop is based on the alignment of two capillaries immersed in a pressurized chamber containing the continuous phase. The dispersed phase exits one of the capillaries through a 3D-printed nozzle, placed in front of the extraction capillary for collecting the droplets. This non-embedded implementation of an axisymmetric flow-focusing is referred to co-flow-focusing.

Fluigent high-speed camera is a package that contains all necessary instruments to have a good optical device.

It contains:

  • Microscope
  • High-speed camera
  • Light controller

This package is connected with a USB 3.0 wire to a PC where the user can visualize its microfluidic device with the Pixelink Capture Software together with other Fluigent Software (MAT, A-i-O). The camera has been selected to reach rates up to 7028 fps, ideal for droplet experiments. 

Figure 1: Scheme of the fluidic setup

Figure 2: Pictures of the Fluigent equipment

Results

Continuous phase flowrate
(μl/min)
Droplet phase flowrate
(μl/min)
Droplet diameter
(μm)
Production rate
(Hz)
100
5
63
637
100
10
67
1058
100
15
73
1227
50
5
71
445
50
10
75
754
50
15
82
866
25
5
75
377
25
10
77
697
25
15
81
898
15
15
83
835

Figure 3: Droplet phase diagram

 

Figure 4: Images of decane droplets in water generated using Fluigent equipment and Raydrop microfluidic device 

 

Conclusion

Fluigent pressure-based flow controller units and Raydrop microfluidic device were successfully used to generate high-quality, monodisperse droplets of decane in water. The droplet size was controlled in the range of 63 – 83 μm by adjusting the continuous and dispersed phase flowrates. Peak stable droplet production rate was recorded for 73 μm droplets at 1227 Hz. The production techniques developed here can be extended to the generation of wax, p, or polymer beads by adding suitable post-processing steps.

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