A microfluidic toolbox for

emulsions and foams

9 December 2015

Karin Schroën, Kelly Muijlwijk, Claire Berton-Carabin

Food process engineering group

Droplets and bubbles

Making them

Trying to brake them

Trying even harder to break them

Making more in 2 ways (bonus)

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!

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

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Unpublished results Kelly Muijlwijk;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

Benefits of microfluidics

Insights in dynamic surfactant behaviour

● Sub mill-second scale (process conditions)

● Variation of ingredients

But how about stability?

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

Collision chamber

Krebs et al (2012) Lab on a Chip, 12(6), 1060-1070

Coalescence time

Approach

● Linear

Film drainage

● Coalescence

time

Krebs et al (2012) Soft Matter 8(41), 10650-10657

Coalescence time distribution

1 on 1 droplet

Average time

Log normal distribution

Krebs et al (2012) Soft Matter 8(41), 10650-10657

Expected average coalescence time

Process conditions

Volume fraction

Emulsifier

● Concentration

● Type

Krebs et al (2012) Soft Matter 8(41), 10650-10657

Benefits of microfluidics

Insights in coalescence behaviour

● Variation of ingredients (including volume fractions)

● Variation in process conditions

But can we speed this up?

Breaking harder: One step further....

Krebs et al. (2013) Soft Matter, 9(15), 4026-4035

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

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

Micro-centrifuge foam

Relative g-force a/g=10

Xiaoxiao Zhang, Master thesis, 2012

0.1 % whey protein isolate

Benefits of microfluidics

Insights in coalescence behaviour

● Variation of ingredients

● Wider variation in process conditions

● Flexibility

Can we also make more (bonus)?

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

Upscaling Partitioned plateau?

Aiming

● Higher pressure stability

● More droplet formation points

Sahin and Schroën (2015) Lab on a Chip, 15(11), 2486-2495

That is possible (hexadecane/SDS solution)!

9 µm droplets

33 micro-plateaus 100% active

S. Sahin, K. Schroën, 2015, lab on a chip

2 µm

5 µm

10 µm

Next stage.....

Stacked main plateaus with micro-plateaus

S. Sahin, K. Schroën, 2015, lab on a chip

Making more in different ways

10 μm10 μm

Images courtesy Francisco Rossier, Hassan Sawalha, Meinou Corstens

Benefits of microfluidics

Very monodisperse emulsions

● Based on previous designs

● Interfacial tension

● Stability tests

Findings relevant for many fields

● Making

● Breaking

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