INTRODUCTION
An
emulsion is a thermodynamically unstable system consisting of at least two
immiscible liquid phases, one of which is dispersed as globules in the other
liquid phase. It contains both a dispersed and a continuous phase, with the
boundary between the phases called the "interface". Emulsions are
part of a more general class of two-phase systems of matter called colloids.
Although the terms colloid and emulsion are sometimes used interchangeably,
emulsion should be used when both the dispersed and the continuous phase are
liquids.
Common
emulsions are inherently unstable and, thus, do not tend to form spontaneously.
Energy input such as through shaking, stirring, homogenizing, or exposure to
power ultrasound are needed to form an emulsion. Another method to make it
stable is by adding a substance called stabilizing agent .In one method called
HLB (hydrophilic- lipophilic balance) is used to determine the quantity and
types of surfactant (stabilizing agent) needed to make an appropriate emulsion.
This experiment is conducted primarily to determine the effect on adding
emulsifying agent to emulsion.
Whether
an emulsion of oil and water turns into a "water-in-oil" emulsion or
an "oil-in-water" emulsion depends on the volume fraction of both
phases and the type of emulsifier (commonly a surfactant). Emulsifiers and
emulsifying particles tend to promote dispersion of the phase in which they do
not dissolve very well. For example, proteins dissolve better in water than in
oil, and so tend to form oil-in-water emulsions (that is, they promote the
dispersion of oil droplets throughout a continuous phase of water).
OBJECTIVES
1. To
determine the effect on adding HLB surfactant on emulsion stability.
2. To
investigate the effects of content of different emulsifying agents on the
physical appearance and stability of emulsion formulation.
APPARATUS
8 test tubes, 1
measuring cylinder 50ml, vortex mixer, weighing boat, 2 set of Pasteur pipette
and droppers, 1 set of mortar and pestle, light microscope, microscope slide, 1
set of pipette 5ml and bulb, 1 beaker 50ml, 1 centrifuge tube 15ml, coulter
counter, centrifuge, viscometer, water bath (45 ̊ C), refrigerator (4 ̊ C).
MATERIALS
Palm oil, arachis oil,
olive oil, mineral oil, distilled water, span 20, tween 80, sudan solution III
(0.5 %), isoton III solution.
Procedures:
1. Each
test tube was labeled and drew a 1 cm of straight line from the bottom of test
tube.
2. 4
ml of arachis oil was mixed with 4ml of distilled water into a test tube.
3. Span
20 and tween 80 were dropped into the mixture according to the table. Test tube
was closed and put on the vortex mixer for 45s. Time needed to achieve
separation phase was recorded. HLB for each sample was decided.
4. A
few drop of sudan III solution was added to 1 g of emulsion in weighing boat
and flatten. The sample was put on microscope slide and observed. The shape and
size of globules were drew, explained and compared.
5. One
formulation of mineral oil emulsion (50 g) was prepared according to the
formula :
Mineral oil 25ml
Acacia 6.25g
Syrup 5ml
Vanillin 2g
Alcohol 3ml
Distilled water, qs 50
6. 40
g of emulsion was put in beaker 50ml and was homogenized for 2 min with
homogenizer.
7. 2g
of emulsion (before and after homogenization process) put in the weighing boat
and labeled. A few drops of sudan III solution was added and flatten.
8. Viscosity
of the emulsion( 15g in beaker 50ml) after homogenization was determined
through viscometer which calibrated with spindle type LV-4. Then, the sample
was exposed to temperature 45 ̊ C(water bath) for 30min and then temperature 4
̊ C for 30 min. The viscosity was determined after exposed to temperature cycle
and emulsion reached room temperature (10-15 min).
5g of emulsion that homogenized was put in the
centrifuge tube and centrifuged (4500 rpm, 10min, 25 ̊ C). The height of the
separation was measured and ratio of the separation height was determined.
RESULTS
Tube no.
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Span 20(drops)
|
15
|
12
|
12
|
6
|
6
|
3
|
0
|
0
|
Tween
80(drops)
|
3
|
6
|
9
|
9
|
15
|
18
|
15
|
0
|
HLB value
|
9.667
|
10.733
|
11.343
|
12.44
|
13.171
|
14.086
|
15
|
0
|
Separation
time (min)
|
-
|
-
|
-
|
84
|
74
|
98
|
53
|
5
|
Stability
|
No
|
Yes
|
No
|
No
|
No
|
No
|
No
|
Yes
|
Colour sample
after addition of Sudan III
|
-
|
Immediately
turns brick red
|
Turns to brick
red
|
Turns to light
peach
|
Slowly become
light peach
|
Turns to light
orange
|
Turns peach
|
Immediately
turns brick red
|
Time
to become interphase(pm)
|
2.45-
|
2.48-
|
2.49-
|
2.50-4.14
|
2.51-4.05
|
2.52-4.30
|
2.54-3.47
|
2.55-3.00
|
The image of the solution after a few drops of Sudan
solution under microscope:
1st test tube:
2nd test tube:
3rd test tube:
4th test tube:
5th test tube:
6th test tube:
7th test tube:
8th test tube:
Part
2
The texture,
consistency, degree of oily configuration and colour dispersion of sample under
light microscope.
Emulsion
form before homogenation
Emulsion
form after homogenation
Results A (Mineral
Oil-30mL)
Reading
|
Viscosity (cP)
|
Mean+ Standard
Deviation (SD)
|
||
1
|
2
|
3
|
||
Before the
temperature cycle
|
440
|
550
|
570
|
520 ± 70
|
After
temperature cycle
|
2800
|
2900
|
2250
|
2650 ± 350
|
Difference
(100%)
|
134.38%
|
|||
Results B (Mineral Oil—30mL)
Height (mm)
|
|
Interface
|
30
|
Original emulsion
|
50
|
Height ratio
|
3:5
|
DISCUSSION
1. What are HLB values that can produce stable emulsion? Discuss.
From the journal written by Vasiliki Polychniatou,
Constantina Tzia, the HLB values of the used surfactants ranged between 16, 7
to 4,3. In our experiment, surfactant used are Span 20 and Tween 80 which have
surfactant value of 8.6 and 15 respectively. The surfactants with an HLB value
closer to the requested value are expected to be more suitable for
emulsification.
In order to keep the emulsion stable, correct
amount and type of surfactant must be used. This keeps the small droplets
dispersed properly. From the result obtained, the most stable emulsion will be
the one with HLB 9.67. The separation is the least and doesn’t reach 1cm mark
even after few hours.
Surfactant is used to stabilise two immisible layer
by incorporating its hydrophilic head in aqueous phase and hydrophobic tail
with hydrophobic drug particles. At certain concentration of surfactant added,
micelle will be formed and it will try to keep the hydrophobic drug particles or
lipid globules in the core with tail pointing inward center while the head will
remain in aqueous phase. This will lower the interfacial tension thus,
stability and emulsification is enhanced.
Surfactants have HLB values. The HLB value of a
surfactant is determined by the ratio of the weight of the hydrophilic
(water-loving) portion of the molecule to the lipophilic (oil-loving)
molecules. Proper use of the surfactant enable good mixing the two immiscible
phase which are the aqueous phase and oily phase. As a result, the phase of
separation will occur slowly. Usually idea HLB value cannot be obtained
directly. The usage of two or more surfactant will give the required HLB value
leading to a very stable emulsion. This can be observed by the no phase separations
until 1 cm occur after 3 hour for test tube 1 till test tube 7 which use a
combination of Span 20 and Tween 80.
Arachis oil emulsion should have HLB value of 6-7.
In our experiment, the first test tube shows the most stable emulsion compare
to other 7 test tube emulsion. This result is almost compatible with the
required HLB value.
2. Compare the physical structures
for the mineral oil emulsions formed and explain. What is the Sudan III
Solution? Compare the colour dispersion in the emulsions formed and explain.
Sudan III test is a
teat using Sudan III which is oil soluble to show amount and location of
lipids. Sudan III is also a fat-soluble dye used for staining of triglycerides
in frozen sections, some protein bound lipids and lipoproteins on paraffin sections.
Sudan III has the appearance of reddish brown crystals. It stained red in oil.
When the emulsion is oil in water, the Sudan III does not disperse in the
emulsion. While in the water in oil emulsion, the Sudan III colouring will
disperse in the emulsion. In this experiment, Sudan III solution is used to
show the shape and physical
characteristic of oily phase in an emulsion thus determine the type of
emulsion formed. We can classify the emulsion into oil-in-water
emulsion (o/w emulsion) or water-in-oil (w/o emulsion) through this test.
The
phase separation of the emulsions is clearly seen before homogenization.
Moreover, the texture of the emulsions formed before undergo homogenization are
coarse and less viscous. The globules also appeared to be larger in size. The
emulsions are less consistent and feel greasy. The emulsion shows poor colour
dispersion in the emulsions after adding Sudan III solution.
The textures generally are smoother and more after
homogenization as the sample tube is spun in the high rate and the globules are
broken into smaller sizes. The emulsion is also more consistent. The colour of
the emulsions becomes milky in colour after adding Sudan III solution. It also
showed good colour dispersion in the emulsions.
3.
Plot
and discuss
a. Graph
of sample viscosity before and after the temperature cycle vs. the content of
mineral oil.
Mineral
oil (ml)
|
Viscosity
average (cP)
x
± SD
|
Difference in viscosity (%)
|
|
Before
|
After
|
||
20
|
18.93
± 2.04
|
19.30
± 3.98
|
1.95%
|
25
|
1360
± 636.63
|
1180
± 75.50
|
13.24%
|
30
|
4998±0
|
833
± 28.87
|
83.30%
|
35
|
5350
± 334.17
|
6373
± 412.65
|
19.12%
|
From the graph, the
viscosity of the emulsion at room temperature increased when the content of the
mineral oil increased from 20ml to 35ml. However due to experimental errors,
there is a decrease in viscosity when 25ml and 30ml of mineral oil are
subjected to temperature cycle.
Theoretically,
the placement of emulsion samples into the water bath at 450c for 30
minutes in the temperature cycle will cause an increase in viscosity. Decrease
in apparent viscosity of the continuous phase and increased kinetic motion of
the disperse droplets and the emulsifying agent at o/w interface are attributed
to increase in temperature. Therefore, it is placed into into freezer at 40c
for 30 minutes to reduce the kinetic energy of the system, thereby increasing
the viscosity of the continuous phase as well as decreasing the rate of
migration of the globules in the disperse phase. Thus, the viscosity of the
emulsion will increase after the temperature cycle.
However, the result
obtained is not positively associated with the theory. This might be due to
errors made in the measurement of the viscosity. The tip of viscometer might be
place too close to the base of the beaker thus affecting the results obtained.
b. Graf
of the viscosity difference (%) vs. various amount of mineral oil.
From
the graph above, the differences in viscosity fluctuated as the content of the
turpentine oil increased. The various content of the mineral oil will influence
the viscosity of emulsion. Theoretically, higher amount of oil globules in the
continuous phase will increases the viscosity of the emulsion.
5. What are the functions of each
ingredient used? How these different ingredients affect the physical
characteristics and stability of an emulsion formulation?
Acacia
is an emulsifying agent used to increase the viscosity among the interphase of
the oily and aqueous phase. It is a good medium for the microbial growth since
acacia is a natural product. Therefore antimicrobial agent such as benzoic acid
0.1% is added to prevent the emulsion from microbial growth. It is different
from the surfactant which reduce the surface tension.
Mineral
oil forms the dispersed phase in the oil in water emulsion (o/w emulsion). Different
oils with different oil may give rise to different colouration of the emulsion
we obtained. The amount of arachis oil (dispersed phase) and distilled
water (continuous phase) added to form an emulsion will determine the type
of emulsion formed. The stability of
emulsion formed will decrease if the volume of dispersed phase exceeds 50% of
the emulsion. Phase inversion tends to occur for emulsions containing more than
about 70% dispersed phase.
Meanwhile,
vanillin serves as vanilla taste flavouring agent. Syrup is a sweetening agent
and can increase the viscosity of the emulsion too. This is mainly to increase
patient’s compliance. However, the amount of syrup used will affect rheological
and physical properties of the emulsion.
Alcohol
as preservative, is added to emulsion to ensure chemical stability and prevent
microbiological contamination of the emulsion. The emulsion will have stable physicochemical
properties for longer duration. However the amount of alcohol that can be added
to emulsion should not be exceeded as it produces toxicity in larger amount.
CONCLUSION
The surfactants with an HLB value closer to
the requested value are expected to be more suitable for emulsification. From
the result of the experiment, the most stable emulsion will be the one with HLB
9.67. While, acacia is an emulsifying agent used to increase the viscosity
among the combined phase of the oily and aqueous phase. The higher the amount
of emulsifying agent used, the higher the viscosity of the interphase. So the
globules also appeared to be smaller in size. Thus, the solution is tends to be
more stable.
REFERENCE
i. Liquids and their interfaces. http://www.chem1.com/acad/webtext/states/liquids.html.
Retrieved on: 16/4/2014
ii. Concentration-dependent,
temperature-dependent non-Newtonian viscosity of lung surfactant dispersions.
PubMed. http://www.ncbi.nlm.nih.gov/pubmed/11518568.
Retrieved on: 17/4/2014
iii. Surfactants: the ubiquitous
amphiphiles. Royal Society of Chemistry. http://www.rsc.org/chemistryworld/Issues/2003/July/amphiphiles.asp.
Retrieved on: 20/4/2014
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