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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
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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