1 Preparation and Characterization of Oil-in-Water and Water-in-Oil Emulsions Prepared For Dr. Reza Foudazi, Ph.D. Chemical and Materials Engineering New Mexico State University By Muchu Zhou May 10, 2016
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Preparation and Characterization of
Oil-in-Water and Water-in-Oil Emulsions
Prepared
For
Dr. Reza Foudazi, Ph.D.
Chemical and Materials Engineering
New Mexico State University
By
Muchu Zhou
May 10, 2016
2
1 Introduction
1.1 Purpose of This Report
The objective of this report is to clarify what I have done this semester for
research course CHME 498. The research interest is “Preparation and
Characterization of Oil-in-Water and Water-in-Oil Emulsions”. Thus, I would like
to talk about what is emulsion, what are the main characteristics of emulsions,
what are the existing methods for preparations of emulsions and how to make
simple emulsions.
1.2 Background of This Report
Emulsion is a kind of mixture comprised of two or more liquids, which usually
are immiscible, and surfactant. The common types of emulsions are oil-in-water
emulsion and water-in-oil emulsion. According to Aronson (1988), the emulsions
have important industrial value in the wide range of field and it has been studied
extensively recently. The emulsions play an important role in the industrial
production and it has been applied to many fields including food industry,
cosmetics industry and pharmaceutical industry. In the food industry, emulsifier
can function as dough conditioners in order to improve tolerance to variations in
flour and other ingredient quality. In the cosmetic industry, the majority of facial
creams and lotions are emulsions.
1.3 Scope of This Report
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This report is going to cover the following contents.
Introduction of emulsions.
Effect of surfactant.
Common materials for preparation of emulsions.
Main methods to make emulsions.
How to make simple emulsions.
Conclusions.
2 Emulsions
2.1 Introduction to emulsions
What is emulsion? Emulsion is two or more different immiscible liquids with a
surfactant. Thus, there is going to be two phases, one is continuous phase and
another one dispersed phase. Generally speaking, the two phases are oil phase
and water phase. Generally speaking, there are two common types of emulsions,
one is oil-in-water emulsion, and another one is water-in-oil emulsion. The
oil-in-water emulsion is usually common.
Figure 2-1-1: Introduction to emulsion
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Mason, T., Wilking, J., Meleson, K., Chang, C., & Graves, S. (2006).
Nanoemulsions: Formation, structure, and physical propertites.
Figure 2-1-2: The types of emulsion
2.2 Instability of Emulsions
According to Aronson (1988), there are two main kinds of instabilities of
emulsions, which are flocculation and coalescence. The flocculation is a
reversible aggregation of droplets, which could result in phase separation in the
field of gravity. Compare with flocculation, coalescence is caused by the
rupturing of film of the continuous phase and it is a fusion of droplets into a
larger droplets so that there will be separation of emulsion into discrete bulk
phases.
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Figure 2-2-1: Flocculation
Figure 2-2-2: Instability of emulsions
2.3 Microemulsion and Nanoemulsion
Moreover, there is existing microemulsion and nanoemulsion. Microemulsion
is a kind of thermodynamically stable isotropic liquids including oil, water and
surfactant. In the most microemulsion phases, the surfactant is highly soluble in both
liquid phases. However, the nanoemulsion is a type of traditional emulsion and the
droplets size is different.
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According to Gupta (2010), the composition of the microemulsion and
nanoemulsion are similar, are oil, water and surfactant. The droplets size is similar
either. And the particle structure is similar, which is small spherical particles
consisting of oil and surfactant molecular dispersed in the water phase. Yet they are
absolutely different since the nanoemulsion is formed by mechanical shear and the
micro emulsion is formed by self-assembly, that is why the microemulsion could be
made without and external energy.
3 Effect of Surfactant
The surfactant is so significant, because surfactant affects the emulsification in
many ways.
3.1 Lowers interfacial tension
If two immiscible liquids are in contact with each other, they will tend to
maintain as small as interface as possible. Consequently, it is very difficult to mix
them. When you shake them, they will become spherical droplets, but after a while,
there will be phase separation since the liquids tend to maintain as small a surface
area as possible and an interfacial tension will be maintained. However, when a
“surface active” ingredient is added, its molecular will tend to be oriented between the
two faces with the polar ends in the polar phase and non-polar ends in the non-polar
phase, which will lower the cohesive force.
3.2 Allows an interfacial tension gradient dγ/dz to exist
The presence of surfactant allows an interfacial tension gradient to exist which
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implies that the tangential stress and velocity are no longer continuous across the
droplet boundary, and the internal circulation in the droplet is impeded or even be
prevented. It facilitates droplet deformation, hence breakup.
3.3 Coalescence is slowed down
The instability coalescence is slowed down, it enhance the stability.
3.4 Interfacial instability can facilitate emulsification
Interfacial instability may be occur, it facilitates the emulsification process.
4 Common materials for preparation of emulsions
The common oil phases are the list as below.
Density kg/m3 Boiling
Point C。
Viscosity
mPa·s
Structure
Silicone Oil 965-980(25C。) >140 100
Refined
Sunflower
Oil
920(20C。) 232 68
Paraffin Oil 800(25C。) 260 0.001 /
Table 4-1: Common Oil Phases
The common surfactants are the list as below.
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Melt
Point C。
Density kg/m3 Structure
PGPR 90 / /
SDS 204-207 1010
F 68 52 /
Table 4-2: Common Surfactants
5 Main methods to make emulsions
There are many ways to produce emulsions. What I used is injection and stirring.
Injection method is that the disperse phase (oil phase) is injected into the continuous
phase and then it could be broken into large droplets. And stirring method is that using
some equipments to make emulsion mixed homogenously and broke the large
droplets into smaller one.
6 How to make simple emulsions
What I have done is made some emulsion samples. The main method is
combination of injection with stirring. The procedure is the following steps:
Weight the surfactant.
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Add water.
Stir the liquid.
Add silicone oil slowly using syringe pump.
Stir the mixture for mixing homogeneously.
Reduce the droplet size by the shear stress.
The following figures are the samples.
Figure 6-1: Sample with Ф = 0.4 silicone oil and wt% 1.0 SDS
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Figure 6-2: Sample with Ф = 0.4 silicone oil and wt% 5.0 SDS
Figure 6-3: Sample with Ф = 0.4 silicone oil and wt% 10.0 SDS
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Figure 6-4: Sample with Ф = 0.3 silicone oil and wt% 5.0 Pluronic F68
Figure 6-5: Sample with Ф = 0.4 silicone oil and wt% 5.0 Pluronic F68
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Figure 6-6: Sample with Ф = 0.3 silicone oil and wt% 5.0 SDS
Figure 6-7: Sample with Ф = 0.4 silicone oil and wt% 5.0 SDS
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7 Conclusions
Figure 7-1: Observation through Microscope
The figure as above is oil-in-water emulsion I made through microscope. The
black line is from ruler which is 1mm length. The sample composition is wt% 5.0
SDS and Ф0.4 silicone oil. According to measurement, the max diameter is about 44
μm, and the min diameter is about 11μm. Thus, we can conclude that the droplet
size is larger than we expected.
The new question I need to think about is how to make the droplet size become
much smaller. Increase the agitation energy means higher rotating speed when mixing
two phases. If there is higher mixing speed, more shear stress could be obtained and
the shear stress is significant in the disruption of droplets. The objective is to generate
smaller stable droplets. We want to have rapid adsorption, lower the interfacial
tension and form protective membrane. And we want to control the droplet size, so the
disruption of droplet size is significant.
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8 Appendix
Method Related
to
method
Drop
formation
Drops
manly
disrupted
bya
Energy
densityb
Mode of
operationc
Restrictionsd
1.Shaking 4a + (T) L B N
2.Pipe flow
a.Laminar 5 (+) V L - M C V
b.Turbulent
4a + T L - M C N
3.Injection 10a + - L C
4.Stirring
a.Simple
stirrrer
1, 2b + T, V L B, C
b.Rotor-
stator
(5) + T, V M - H B, C
c.Scraper 5 + V L - M B, C V
d.Viberator
8a + ? L B, C N
5.Colloid
mill
2a, 4c, 6 (+) V M - H C V
6.Ball and
roller mills
5 + V M B (C) V
7.High-press.
homogenizer
(2b) - T, C, V H C N
8.Ultrasonic
a.Vibrating
knife
4d + C, T M - H C W
b.Magneto-
striction
+ C M - H B, C W
aV = viscous forces in laminar flow, T = turbulence, C = cavitation. bL = low, M = moderate, and H = high. cB = batch and C = continuous dThe continuous phase should be V = viscous, N = not too viscous, W = aqueous.
(This table is from “Encyclopedia of Emulsion Technology, Volume 1”)
9 References
Aronson, M. P. (1989). The role of free surfactant in destabilizing oil-in-water
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emulsions. Langmuir, 5(2), 494-501.
Elbers, N. A., Jose, J., Imhof, A., & van Blaaderen, A. (2015). Bulk Scale Synthesis of
Monodisperse PDMS Droplets above 3 μm and Their Encapsulation by Elastic
Shells. Chemistry of Materials, 27(5), 1709-1719.
Fryd, M. M., & Mason, T. G. (2012). Advanced nanoemulsions. Annual review of
physical chemistry, 63, 493-518.
Gupta, A., Eral, H. B., Hatton, T. A., & Doyle, P. S. (2016). Nanoemulsions:
formation, properties and applications. Soft matter, 12(11), 2826-2841.
Márquez, A. L., Medrano, A., Panizzolo, L. A., & Wagner, J. R. (2010). Effect of
calcium salts and surfactant concentration on the stability of water-in-oil (w/o)
emulsions prepared with polyglycerol polyricinoleate. Journal of colloid and
interface science, 341(1), 101-108.
Mason, T. G., Wilking, J. N., Meleson, K., Chang, C. B., & Graves, S. M. (2006).
Nanoemulsions: formation, structure, and physical properties. Journal of Physics:
Condensed Matter, 18(41), R635.