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The Principles of Emulsion Formulation

ByWim Agterof

Unilever Research, The NetherlandsTechnical University of Twente, The Netherlands

New Developments in the Formulation of DispersionsRSC Formulation Science and Technology Group

Umist, Manchester, 2003

Content

Droplet break-up Coalescence Phase inversion Computational approach

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EMULSIONS

Water in oil Oil in water

Duplex emulsies

continue fase

primaire disperse fase

secundaire disperse fase

bv. W/O/W emulsie:

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Double EmulsionDouble Emulsion

Emulsification

Physico-chemical aspects: Interface:tension, visco-elasticity

Multiphase flow aspects: vessel droplet break-up coalescence

4

Droplet break-up

Hydrodynamic and interfacial forces:

σ/Rflow

ηγ.

Capillary number Ca=ηγR/σ.

Grace Curve: binary break-up

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Break-up and EmulsifierBreak-up and Emulsifier

Grace curve

λ

φ= 0: Ωcr = fGr (λ )φ> 0: Ωcr = f (λ , φ )

Rheology group Twente

The Netherlands

Ωcr

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Assumption: break-up depends on the emulsion viscosity η (ϕ ) = ηr (ϕ )ηs instead of ηs

Ω * = η(ϕ) aγ’ /σ

λ* = ηd / η(ϕ)

For ϕ > 0 :

Ω *cr = fGr (λ*)

Rheology group Twente

The Netherlands

Ω*cr

Break-up Mechanisms

Binary break-up Capillary break-up

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Capillary break-up: simple shearflow

Transient binary break-up

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Colloid Mill

Population Balance MethodSplit particle size distribution up in i classes having number-density ni

Ki,j=1/tb

jijj

ii nKK

tn

,1

1, ∑>

+−=∂∂

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PSD evolution in colloid mill

Colloid Mill Droplet Size

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Colloid Mill: size distributions

Sulzer Mixer SMV

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Capillary break-up: elongational flow

Results Sulzer SMV

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Coalescence

Interaction time and force

1 32

4a

< deq or4b

interaction time:

interaction force:

ti = 1&γ

F di c eq= 32

2π µ γ&

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CoalescenceCoalescence rate=collision rate ×

coalescence probability (P)

PtKdt

Nd γφπ4)(ln ==−

)/(exp cdP ττ−=

.

Coalescence Modes

Rigid solids

Immobile droplets deformable

Fully mobile (inviscid)

Partially mobile

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Coalescence: Film Drainage

Coalescence Probability

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Coalescence Frequency

PSD during coalescence

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10 -3 10 -2 10 -1 10 0

Pc_exp

10 -3

10 -2

10 -1

10 0

Pc_mod

Optimal result for α = 1.18, β = 0.79, Ro = 5.7 µm

Coalescence in a stirred vessel

0.0E+00

2.0E-04

4.0E-04

6.0E-04

8.0E-04

1.0E-03

1.2E-03

1.4E-03

1.6E-03

0% 20% 40% 60% 80% 100%

v olume fraction oil

diam

eter

(m) 400 RPM

750 RPM1000 RPM1450 RPM

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Phase Inversion

Phase Inversion: Emulsifier

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Escape

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Escape: mechanism

1:

2:

Inversion after stirring

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Particle size evolution before inversion

Homogeneous flow: no inversion

0,00

0,000,010,020,030,040,050,060,070,080,090,10

1,00E-05 1,00E-04 1,00E-03

diameter[m]

geno

rmal

isee

rd v

olum

e

0,000,010,020,030,040,050,060,070,080,090,10

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PSD in shear distribution

0,00

0,000,020,040,060,080,100,120,140,160,180,20

1,00E-05 1,00E-04 1,00E-03

diameter[m]

geno

rmal

isee

rd v

olum

e 0,00,10,30,50,81,02,010,0

Diameter development on inversion

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Effective volume fraction increasebefore inversion

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ERFProcess Principles

Unilever ResearchVlaardingen

0 200 400 600 800 10000

0.0002

0.0004

0.0006

0.0008

0.001

t (s)

d (m

)

Break-up: experiments

Blue Band vloeibaar

W/O emulsion

SF oil

He-Ne laser

Photo diode

I(t)

d32

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The Sγprinciple

ν Definition of Sγ:

ν Properties of Sγ:λ Sγ is conserved on a volumetric basisλ Any n-parameter distribution is fully characterised by n

different Sγ valuesλ S3 is related to the volume fraction:

( )S nd P d dγγ=

∞

∫ d0

S36

=π

ϕ

S!-Transport equationS!-Transport equationS!-Transport equation

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0 200 400 600 800 10000

0.0001

0.0002

0.0003

0.0004

0.0005

t (s)

d (m

)

µc = 60 mP a .s

N = 250 RP M

N = 500 RP M

Simulation and Experiment

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Conclusions Droplet break-up is understood quite well,

except for viscoelastic fluids Coalescence is not understood quantitatively

especially because good experimental data are missing

Phase-Inversion is getting out of its trial and error approach

There is progress in a computational approach Theory helps in the design of processes

Acknowledgement

• Jo Janssen• Jan Wieringa• Jurgen Klahn• Allan Chesters• Dirk van de Ende• Jorrit Mellema

• Wim van Evert• Roland de Swart• Sasha Korobko• Kaspar Jansen• David Gosman• Raad Issa• Frans Groeneweg

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Escape modelling: concept

ic

cri

tP2

tϕαϕ =−

dd

fraction of internal phase

fluid circulation timein droplet

coalescence probabilityescape range

escape rate

Escape modelling:escape range

αcr depends on: diameter ratio shape of streamlines (i.e. on λ)

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Droplet Break-upDroplet Break-up