Influence of Emulsifiers on Stability andRheological Properties of Concentrated Oil in
Water Emulsions
Masami Kawaguchi

Division of Chemistry for Materials, Graduate School ofEngineering, Mie University, 1577 Kurimamachiya, Tsu,
Mie 514-8507, JAPANOutline
1. Introduction
2. Emulsions prepared by polymeric emulsifiers
3. Conclusions for the emulsions prepared bypolymeric emulsifiers
4. Pickering emulsions
5. Conclusions for Pickering emulsions

Introduction
Emulsions, i.e. dispersions of liquid droplets
stabilized by emulsifiers in a continuous liquidmedium, are very interesting objects forrheological investigations. Studies of emulsions
under shear flow have long been a subject of boththeoretical and experimental interest and various
systematic results have been reported.
Emulsions are not thermodynamically stablestates and they are metastable dispersions.

Diagram of the free energy and entropy change ofa system during emulsification∆G or ∆SDropletsγ∆A increases−T∆S decreases∆G = γ∆A − T∆Sγ∆A >> T∆S
Two separatephases∴ ∆G = γ∆AEmulsification

Since emulsions are metastable dispersions,instability of emulsions, such as Ostwald
ripening and coalescence are not negligible.
Ostwald ripeningCoalescenceOn the other hand, other instabilities such as creaming andaggregation also occur after preparation of emulsions.

Creaming

Aggregation

Emulsification

C regniamAggregation

Changes in rheological properties by packing of droplets
DiluteConcentrated
Randomly close Compressed

φ: Volume fraction of droplets in emulsified phase
G sm = 2

σ in
D 3,2

φ (φ − 0 . 64 )( Mason − Bibette − Weitz )Characterization of emulsions
1. Type of emulsions (Dilution method)
2. Amounts of adsorbed emulsifiers(Spectroscopic techniques)
3. Droplet Size distribution (Coulter counter,Optical microscope)
4. Stability of emulsions (Optical methods)
5. Interfacial properties
6．Emulsion rheology

In this presentation, we will force on stability andrheological properties of silicone oil droplets stabilized bysome emulsifiers such as water-soluble polymers and silica
particles pre-adsorbed polymers in water. The respective
emulsifiers were adsorbed on the silicone oil droplets. The
resulting oil in water (O/W) emulsions were classified into
concentrated emulsions because their volume fraction of oildroplets in the emulsified phase was greater than 0.6.
Rheological properties of the corresponding O/W emulsions
have been carried out by the measurements of stress-strain
curve together with the optical microscopic observation ofchanges in oil droplets under shear flow, and oscillatory
shear viscoelasticity.

Emulsifiers
Polymeric emulsifiers: Hydroxyl propyl methyl
Cellulose (HPMC), PEO-PPO-PEO, Poly-N-isopropyl
acrylamide (PNIPAM) . Their aqueous solutions
were surface active, leading to a decrease in thesurface tension.
Silica particles: Hydrophilic Aerosil130 fumed silica
and hydrophobic Aerosil R-972 fumed silica (silanecoupling modification of silanol groups of 130 withdimethyldichlorosilane)
Silica particles pre-adsorbed polymers: Aerosil 130
and Aerosil R-972 silica particles were pre-adsorbed
by HPMC and PNIPAM below at the plateau regionof adsorption isotherm of the respective polymers.
The silica particles pre-adsorbed polymers wererinsed with water to remove the free polymers.

Features of emulsions stabilized bypolymeric emulsifiers
Formation of an adsorbed polymer film layer thickness h on
droplet surface provides that
1) a lager effective volume fraction φeff ≈ φ[1 + 3h / D] , where D
is the droplet diameter (D>>h),2) a decrease in the deformation of the interface,3) an increase in the repulsive forces between droplets.

Adsorbed polymeric emulsifiers in the schematic representation
is extremely exaggerated.

Emulsions prepared by HPMC and PEO-PPO-PEO
HPMC: 60SH-400
Mw = 380 x 103
C* = 0.172 g/100 mL

HOHO-R
HO-RHHOCH 3 -O-R

HO

CH 3 -O-R
O
HHO-R
H
HO-Rn

R : -CH 3 , -CH 2 CH(OH)CH 3 , -H
DS = 1.8

MS = 0.25

PEO-PPO-PEO: F-108, 80 wt% PEO, Mw = 15.5 x 103
Silicone oil: KF96L-1 (1 cSt), KF96-10 (10 cSt), KF96-100 (100 cSt),
KF96-1000 (1000 cSt)
Interfacial tensions of the oil/aqueous solution of HPMC and PEOPPO-PEO are 17.3 and 8.4 mN/m, respectively.
Preparation of emulsions: 25g of silicone oil were agitated with 50g of0.5g/100 mL aqueous solution of HPMC or PEO-PPO-PEO for given
times ranging from 10 s to 60 min at 8000 rpm and 25 oC.

abcdIII50 µm

Optical microscopic images of silicone oil droplets preparedby HPMC (I) and PEO-PPO-PEO (II): silicone oil with kinetic
viscosity of 1 (a), 10 (b), 100 (c), and 1000 cSt (d).

120
φ = 0.72

D3,2(µm)

100
80
60
40200

◇: 1 cSt△: 10m n D3D3 ,2 = ∑ i i2i =1 ni Di

01020□: 100○: 1000

3040506070time (min)Plots of Sauter size D3,2 of oil droplets of the emulsions prepared byHPMC as a function of agitation time for different silicone oils.

6(g/g)

3A x 104-452◇: 1 cSt△: 1010□: 100○: 1000

0102030405060

70time (min)Plots of the adsorbed amounts of HPMC on oil droplets as a functionof agitation time for different silicone oils.

Rheoscope１

2

Shear stress (Pa)10HPMCPEO-PPO-PEO

101
100-1

1010-2
10-2

100

102

104

106

Strain (%)
Stress-strain curves of the emulsions prepared by HPMC and PEO-PPO-PEO for 1cSt silicone oil, together with the optical microscopic images of the corresponding
emulsions at given strains. A red circle in each image indicates the same oil droplet.

3Shear Viscosity (Pas)

10HPMC-1
HPMC-100
F108-1
F108-1002

10110100-1

10-2

10-2

10-1

100

10

1

10

2

10103

Shear rate (1/s)
Plots of shear viscosities of the emulsions prepared by HPMC (opensymbols) and PEO-PPO-PEO (filled symbols) as a function of shear
rate for different silicone oils:1 cSt (circles); 100 cSt (squares).210G', G" (Pa)101
01010-1

G' HPMC-100
G" HPMCG' PEO-PPO-PEO
G" PEO-PPO-PEO

10-210-3-1

10100

11010

2Frequency (rad/s)
Plots of G’ (open symbols) and G” (filled symbols) of the emulsions
prepared by HPMC (circles) and PEO-PPO-PEO (squares) as a functionof frequency for 100 cSt silicone oil

Comparison of the measured G’ and the calculated one ofthe emulsions prepared by HPMC for different silicone oils
Oil viscosity D3,2(cSt)(µm)
110100100037.645.3
60.7
85.9

Measured G’
at 1 rad/s (Pa)Calculated G’(Pa)

123
74.1
49.7
34.2

64.5
53.7
40.9
31.5

Calculated G’ = φeff(φeff - φc)2σin/D3,2; φeff = φ(1 + 3h/ D3,2), where φc is thevolume fraction of the random close-packing (0.64), σin is an interfacialtension (17.3 mN/m), φ is the volume fraction of the emulsion (0.72), and h is
the adsorbed polymer layer thickness (20 nm).

Emulsions prepared by PNIPAMPNIPAM: PNIPAM-80 (Mw = 833×103, C* = 0.85 g/100 mL),PNIPAM-150 (1.54 x 106 , C* = 0.62 g/100 mL), PNIPAM1000 (1.01 x 107 , C* = 0.23 g/100 mL)
CH2 CHOn CH3

N C CH3
HCH3

Silicone oil: KF96L-1; Kinetic viscosity = 1 cSt
Interfacial tension of oil/aqueous solution of PNIPAM =12.3 mN/m
Preparation of emulsions: 10g of silicone oil were agitatedwith 20g of aqueous solutions of PNIPAM with different
concentrations for 30 min at 8000 rpm and 25 oC.

Characteristics of the emulsions prepared by PNIPAM
0.5g/100 mL
PNIPAM-80

1.3g/100 mL
PNIPAM-150

D3,2 = 43.2 µm

D3,2 = 34.1 µm

Just

Deminiere et al. predicted a linear
decreasing relationship between thereciprocal of square of the droplet
size and the evolution time

D3,2 = 55.2 µm

D3,2 = 35.7 µm

1 week100 µmAdsorbed amount of
Adsorbed amount of
PNIPAM = 1.17 mg/g
PNIPAM = 1.78 mg/g

1/(D3,2)2 x 104 (1/µm2)

6PNIPAM150 0.5wt%
PNIPAM80 0.5wt%

543050100

Time (h)150200Stress (Pa)10210110010-110-2-110100101102103104105106Strain (%)
Stress-strain curves of the emulsions prepared by 1.7 g/100 mL PNIPAM-80 (△),
1.3 g/100 mL PNIPAM-150 (□), and 0.5 g/100 mL PNIPAM-1000 (○), together
with the optical microscopic images of the corresponding emulsions at givenstrains. A red circle in each image indicates the same oil droplet. The respective
PNIPAM concentrations correspond to 2C*.

Shear viscosities of the emulsions prepared by PNIPAM
1Viscosity (Pa s)

100.5 g/100 mL PNIPAM-1000
0.5 g/100 mL PNIPAM-150
0.5 g/100 mL PNIPAM-80
1.3 g/100 mL PNIPAM-150
1.7 g/100 mL PNIPAM-80

10010-110-2 010101102

Shear Rate (1/s)

103

Dynamic moduli of the emulsions prepared by PNIPAM

G', G" (Pa)103
G' :0.5 g/100 mL PNIPAM-1000
G': 1.3 g/100 mL PNIPAM-150
G': 1.7 g/100 mL PNIPAM-80
G": 0.5g/100 mL PNIPAM-1000
G": 1.3 g/100 mL PNIPAM-150
G": 1.7 g/100 mL PNIPAM-80

10211001010-1100101102

Angular Frequency (rad/s)

Conclusions for the emulsions prepared by polymers
1. HPMC, PEO-PPO-PEO, and PNIPAM are useful to prepare
O/W emulsions.
2. The emulsions prepared by HPMC showed solidlike viscoelastic responses, whereas the emulsions prepared by
PEO-PPO-PEO indicated liquidlike viscoelastic behavior.
Moreover, the simultaneous optical microscopic observation
showed that the emulsions stabilized by HPMC do not flow
below the yield stress and beyond the yield stress themovements of oil droplets occur first.
3. The emulsions prepared at twice C* of PNIPAM showedsolidlike viscoelastic responses. On the other hand, below
C* the emulsions cause coalescence.

Pickering emulsions
Emulsions stabilized by solid particles are wellknown as Pickering emulsions. The solid particles
were ranged from inorganic materials to organic
ones. The contact angle θ between oil-waterinterface is an important parameter to determine
the type of Pickering emulsion.

R. J. G. Lopetinsky, J. H. Maliyah, and Z. Xu,
in Colloidal Particles at Liquid Interfaces,eds. B. B. Binks and T. S. Horozov,
Cambridge Univ. Press, p. 186 (2006).

Bilayer Stabilization

Bridging by asingle layer

2-D network

Domains ofparticles

3-D network

Emulsions stabilized by silica particles
Aerosil-130: specific area = 130 m2/g, silanol density =2.5/nm2
Aeosil-R972: specific area = 110 m2/g, silanol density =0.2/nm2
Silicone oil: KF96L-1; Kinetic viscosity of 1 cSt

Preparation of emulsions: 15 g of silicone oil were mixed
with 30 g of water dispersions with 0.45g of Aeosil-130;
10 g of silicone oil dispersions with 0.3g of Aerosil-R972
were agitated with 20g of water for 30 min at 8000 rpm
and 25 oC.

Emulsions prepared by Aerosil silica particles
130: O/W emulsion
Stress-strain curves

R972: W/O emulsion

Stress (Pa)

102

101

100
130
R972

10-1 -2
10100

102

104

Strain (%)
100μm

106

Emulsions prepared by silica particles
pre-adsorbed HPMC
Emulsifiers: Aerosil-130 particles pre-adsorbed by HPMC
(Mw = 380×103, C* = 0.172 g/100 mL) below at the plateau
region of adsorption isotherm of HPMC (0.14 g/g) were
washed out to remove the free HPMC.
Silicone oil: KF96L-1; Kinetic viscosity of 1 cSt
Preparation of emulsions: 15 g of silicone oil were mixed
with 30 g of water dispersions with 0.45 g of Aeosil-130
pre-adsorbed HPMC were agitated for 30 min at 8000 rpm
and 25 oC.

Optical microscopic images of the emulsions

Silica only
100μm

D3,2 = 113 µm
HPMC：0.015g

HPMC：0.030g

HPMC：0.050g

HPMC only
100μm

D3,2 = 50,4 µm

100μm

D3,2 = 46.7 µm

100μm

D3,2 = 41.1 µm

Silica preadsorbed
HPMC
100μm

D3,2 = 81.4 µm

100μm

D3,2 = 27.0 µm

100μmD3,2 = 14.5 µm

Characteristics of the emulsions prepared by the hydrophilic
silica particles pre-adsorbed HPMC
Silica (g)φrel

Ad (mg/g)

0.015

0.0

1.0

1.0

50.4

17.3

0.030

0.0

1.0

2.0

46.7

17.3

0.050

0.0

1.0

3.3

41.1

17.3

0.0

0.45

0.8

0.0

113

36.8

0.015

0.45

0.95

17.2

81.4

36.6

0.030

0.45

0.89

22.4

27.0

36.3

0.050

0.45

0.82

30.4

14.5

20.5

HPMC (g)D3,2 (µm) σin (mN/m)

G' (Pa)

103

102

101
10-1

45-0
0-1.5
0-3.00-5.0

100

45-1.545-3.045-5.0101

102

Angular frequency (rad/s)
G’ of the emulsions prepared by Aerosil-130 pre-adsorbed
HPMC, HPMC, and Aerosil-130

Shear stress (Pa)

102

101

100
Silica-HPMC
HPMC
Silica10-1 -2
10100

102

104

106

Strain (%)
Stress-strain curves of the emulsions prepared by silica (△)、HPMC (□) and silica pre-adsorbed by HPMC (○). HPMC = 0.050g

Emulsions prepared by Aerosil-130 and AerosilR972 silica particles pre-adsorbed ＰＮＩＰＡＭ
Emulsifiers: Aerosil-130 and Aerosil-R972 particles preadsorbed by PNIPAM below at the plateau region ofadsorption isotherm (0.12 g/g) of PNIPAM (Mw = 492×103
and C* = 1.12 g/100 mL) were washed out to remove thefree PNIPAM.
Silicone oil: KF96L-1; Kinetic viscosity of 1 cSt
Preparation of emulsions: 10 g of silicone oil were mixed
with 20 g of water dispersions with 0.30g of Aeosil-130
and Aerosil-R972 pre-adsorbed PNIPAM were agitated for30 min at 8000 rpm and 25 oC.

Optical microscopic images of the emulsions preparedby Aeosil-130 pre-adsorbed PNIPAMPNIPAM: 0 g

0.00025

D3,2 = 122 µm

128 µm100μm0.00300.01000.020085.3 µm30.5 µm15.7 µm

Optical microscopic images of the emulsions preparedby Aeosil-R972 pre-adsorbed PNIPAMPNIPAM: 0 g

0.00025

D3,2 = 46.0 µm

34.8 µm
100 µm

0.00300.01500.020034.9 µm26.8 µm

24.0 µm

Characteristics of the emulsions prepared by the hydrophilic
and hydrophobic silica particles pre-adsorbed PNIPAMPNIPAM (g)φrel

Ad (mg/g) D3,2 (µm)

Aerosil-130

φrel

Ad (mg/g) D3,2 (µm)
Aeosil-R972

0.0

0.72

0.0

122

1.00

15.0

46.0

0.00025

0.89

0.4

125

0.97

13.4

34.8

0.001

1.00

2.6

146

0.99

12.6

34.8

0.003

1.00

4.2

85.3

0.99

12.6

34.9

0.01

1.00

10.8

30.5

0.98

13.6.

34.8

0.015

1.00

14.6

19.3

1.00

19.2

26.8

0.02

1.00

17.9

15.7

0.82

26.8

24.0

Stress (Pa)

102

101

100

10-1
10-3

130 Only
0.003 g
0.01
0.02

10-1

101

103

105

107

Strain (%)
Stress-strain curves of the emulsions prepared by Aerosil130 pre-adsorbed PNIPAM

10430-030-0.025
30-0.30

G' (Pa)10330-1.030-1.5
30-2.0102
101
100 -1
10010

110210Angular frequency (rad/s)
G’ of the emulsions prepared by Aerosil-130 pre-adsorbed
PNIPAM.

Stress (Pa)

103
102
101
100
10-1 -3
10R972 Only
0.00025 g
0.003 g0.02 g

10-1

101

103

105

107

Stain (%)
Stress-strain curves of the emulsions prepared by AerosilR972 pre-adsorbed PNIPAM

G', G" (Pa)

104
103
102
R972 G'
R972 G"
0.00025 G'
0.00025 G"
0.003 G'
0.003 G"0.02 G'
0.02 G"

101
10-1

100

101

102

Angular frequency (rad/s)
G’ and G” of the emulsions prepared by Aerosil-R972 preadsorbed PNIPAM

Conclusions for the emulsions prepared by silicaparticles pre-adsorbed polymers
1. Silica particles pre-adsorbed HPMC and PNIPAM are usefulto prepare O/W emulsions. The hydrophilic silica particles
pre-adsorbed PNIPAM can fully emulsify silicone oil.
2. With an increase in the adsorbed amounts of polymers, theemulsions prepared the hydrophilic silica particles preadsorbed polymers showed a decrease in the size of oildroplets and an increase in the elastic response.
3. On the other hand, the emulsions prepared the hydrophobic
silica particles pre-adsorbed polymers showed little changes inthe size of oil droplets and the viscoelastic response.

Acknowledgements
Dr. Kazuhisa Hayakawa (Shin-etsu Chemical Co)
Mr. Kenji Kubota
Mr. Kazuma Ozawa
Mr. Noriaki Sugita
Mr. Chikara Morishita
Mr. Tomoyuki Suzuki