a microfluidic toolbox for emulsions and foams · • small droplets / bubbles coalescence channel...
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A microfluidic toolbox for
emulsions and foams
9 December 2015
Karin Schroën, Kelly Muijlwijk, Claire Berton-Carabin
Food process engineering group
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Droplets and bubbles
Making them
Trying to brake them
Trying even harder to break them
Making more in 2 ways (bonus)
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Properties of the product
Volume fraction of the dispersed phase
Droplet/bubble size distribution
● Monodisperse (amount of surfactant)
● Polydispersity (packing density & creaming stability)
Scaling relations to predict size?
Surfactant dynamics?
Coalescence dynamics?
Product formulation?
Use microfluidic tools!
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0
10
20
30
40
50
0.01 0.1 1 10 100Dyn
amic
inte
rfac
ial t
ensi
on
(m
N/m
)
Droplet formation time (ms)
Making: Dynamic interfacial tension
Ca: Capillary number
c: Viscosity
vc : Velocity
: Interfacial tension
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Preparation of emulsions
Starting point: Y-shaped microfluidic junctions
Very short formation times production (milliseconds)
Possibility to work with small droplets (micrometres)
Comparative technology: DVT sub mm, seconds
Unpublished results Kelly Muijlwijk;
Steegmans et al. (2009) Langmuir 25(17) 9751-9758
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Benefits of microfluidics
Insights in dynamic surfactant behaviour
● Sub mill-second scale (process conditions)
● Variation of ingredients
But how about stability?
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Breaking: Stability of emulsions
Combination of emulsion preparation and coalescence
oil
oil
water
water
emulsion emulsion
Krebs et al (2012) Lab on a Chip, 12(6), 1060-1070
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Collision chamber
Krebs et al (2012) Lab on a Chip, 12(6), 1060-1070
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Coalescence time
Approach
● Linear
Film drainage
● Coalescence
time
Krebs et al (2012) Soft Matter 8(41), 10650-10657
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Coalescence time distribution
1 on 1 droplet
Average time
Log normal distribution
Krebs et al (2012) Soft Matter 8(41), 10650-10657
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Expected average coalescence time
Process conditions
Volume fraction
Emulsifier
● Concentration
● Type
Krebs et al (2012) Soft Matter 8(41), 10650-10657
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Benefits of microfluidics
Insights in coalescence behaviour
● Variation of ingredients (including volume fractions)
● Variation in process conditions
But can we speed this up?
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Breaking harder: One step further....
Krebs et al. (2013) Soft Matter, 9(15), 4026-4035
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Coalescence in a centrifugal field
t = 0.03 s 0.26 s 0.41 s 0.56 s 2.91 s 38.5 s
Krebs et al. (2013) Soft Matter, 9(15), 4026-4035
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Also unstable emulsions!
0 s 10 s 100 s
Radius coloured scale bar (μm) 100 200 300 500 1000 20000 front
Feng et al. (2015) Lab on a Chip, 15(1) 188-194
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Micro-centrifuge foam
Relative g-force a/g=10
Xiaoxiao Zhang, Master thesis, 2012
0.1 % whey protein isolate
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Benefits of microfluidics
Insights in coalescence behaviour
● Variation of ingredients
● Wider variation in process conditions
● Flexibility
Can we also make more (bonus)?
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Making more
Van Dijke et al (2009) Lab on a Chip, 9 (19), 2824-2830
From single droplet from one unit, to multiple droplets from one unit
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Upscaling Partitioned plateau?
Aiming
● Higher pressure stability
● More droplet formation points
Sahin and Schroën (2015) Lab on a Chip, 15(11), 2486-2495
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That is possible (hexadecane/SDS solution)!
9 µm droplets
33 micro-plateaus 100% active
S. Sahin, K. Schroën, 2015, lab on a chip
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2 µm
5 µm
10 µm
Next stage.....
Stacked main plateaus with micro-plateaus
S. Sahin, K. Schroën, 2015, lab on a chip
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Making more in different ways
10 μm10 μm
Images courtesy Francisco Rossier, Hassan Sawalha, Meinou Corstens
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Benefits of microfluidics
Very monodisperse emulsions
● Based on previous designs
● Interfacial tension
● Stability tests
Findings relevant for many fields
● Making
● Breaking
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Dynamic interfacial tension
• Short times • Small droplets / bubbles
Coalescence channel
• Flow • Short times
Microcentrifuge
• Compression • Short times
Muijlwijk, Berton-Carabin and Schroën (2015). How microfluidic methods
can lead to better emulsion products, Lipid Technology, 27 (10), 234-236.
Microfluidic toolbox for emulsions/foams