OBJECTIVES
1. To determine the effect of HLB
surfactant on the emulsion stability
2. To study the effect on physical
and stability of the emulsion when the different amount of emulsifying agent
have been used
INTRODUCTION
Emulsion is a 2 phase systems that
thermodynamically unstable. It contains at least 2 immiscible liquid which
internal phase distributed homogenously in the other liquid phase (external
phase). Emulsion can be classified into oil in water emulsion (o/w) and water
in oil emulsion (w/o). Emulsion is stabilizing using the emulsifying agents.
The emulsifying agent can be classified into 4 types, which are hydrophilic
colloid, fine solid phase, surface active agent and surfactant.
The HLB (hydrophilic-lipophilic
balance) have been used to determine the quantity and the type of surfactant
need to be used to prepare a stable emulsion. Every surfactant has it own HLB
range which is from 1 (lipophilic) until 20 (hydrophilic). Normally, the usage
of 2 emulsifying agent will form a very stabilize emulsion preparation. The HLB
value can be determine using the equation below:
APPARATUS
8 tests tube
MATERIALS
Palm Oil
Arachis oil
Olive oil
Mineral oil
Span 20, Tween 80
Sudan III solution
(0.5%)
ISOTON III
solution
Distilled water
PROCEDURES
Group
Type of oils
1,2
Palm oil
3,4
Arachis oil
5,6
Olive oil
7,8
Mineral oil
3. Span 20 and Tween 80 is added
to the mixture according to the amount given
in the table below. The mixture is
mixed using the Vortex mixing machine for
about 45 seconds. The time taken for
separation to occur until it reaches the 1cm
marked is recorded. The HLB value for
each sample is determined.
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
9.67
10.73
11.34
12.44
13.17
14.09
15.00
0.00
Phase separation time
(min)
>2h
>2h
>1h30min
>1h25min
>1h30min
>1h25min
28.22
3.10
Stability
Most
stable
Most
stable
More
stable
Stable
More
stable
Stable
Not
stable
Not stable
4. A
few drops of the Sudan III mixture is dropped into 1g
of each of the emulsion formed in the weighing boats. The color dispersion is
described and compared with other emulsion formulation. The emulsion is
observed under the light microscope. The structure and globule size are
determined and drawn to compare with other emulsion.
5. Using wet gum method, Mineral
Oil Emulsion (50g) is prepared using formulation below.
Mineral oil
Referred Table III
Acacia
6.25g
Syrup BP
5ml
Vanillin
2g
95% Ethanol
3ml
Distilled water
qs 50ml
Emulsion
Group
Mineral oil (ml)
I
1,2
20
II
3,4
25
III
5,6
30
IV
7,8
35
6. 40g emulsion formed is placed
in beaker and homogenize 2min using
homogenizer machine.
7. 2g of sample before and after
been homogenized is taken out and placed in
weighing boats and labeled. Sudan
III solution is dropped into emulsion. Texture,
consistency, appearance of oil
and color dispersion is determined, and compared
and observed under light
microscope.
8. 15g of the emulsion that have
been homogenized is taken and the viscosity is
determined using the viscometer
that has been calibrated using the “Spindle” LV-4
type. The sample is placed at
45oC (water bath) for about 30 minutes and at 4oC
(freezer) for 30 minutes afterward. The sample that has been exposed to
temperature cycle is then allowed to reach room temperature (10-15minutes). The
viscosity is determined afterward.
For 20 ml of mineral
oil:
Reading
Viscosity (cP)
Average + SD
1
2
3
Before temperature cycle
18.9
20.7
17.2
18.93 + 2.0422
After temperature cycle
18.2
22.1
17.6
19.30 + 3.9800
Difference (%)
1.95%
9. 5g of the emulsion that has
been homogenized is placed into centrifuge tube
and is centrifuged in 4500rpm,
for 10 minutes at 25oC. The separation height
produced is measured
and the ratio of separation height is determined.
For 20 ml of mineral oil :
Height (mm)
Separation phase
2.6
Initial emulsion
5.6
Ratio of height
0.57
CALCULATION
Calculation of HLB values:
RESULTS AND DISCUSSION
1. What are the HLB values to form a stabile emulsion? Discuss.
The HLB value is an indication of the
solubility of the surfactant where the lower the HLB value, the more lipophilic
or oil soluble the surfactant is and the higher the HLB value, the more water
soluble or hydrophilic the surfactant is. Emulsifiers with HLB values ranging
from 3 to 6 will produce water-in-oil emulsions which are stable. On the other
hand, in order to produce oil-in-water emulsions which are stable, emulsifiers
with HLB values ranging from 8 to 18 should be used. For the HLB value between
7-9, emulsifying agents normally act as wetting agent, while between 13-15,
they act as detergents, and value of 15-16, they are become solubilizing agent.
The HLB value for each tube increase
from tube 1 to tube 7. For this experiment, we had use Span 20 and Tween 80 as
the surfactants in the emulsion. A surfactant is used to stabilize both the oil
and aqueous phase which are immiscible. They act by reducing the surface
tension and decreasing the coalescence of dispersed droplets in the emulsion
formed. Hence, the phase separation will occur more slowly. Span 20 has HLB
value of 8.6 while tween 80 has HLB value of 15.
We can determine the stability of an
emulsion more easily from the separation phase time. Emulsion which has the
longest separation phase time is the most stable emulsion. A stable emulsion
contains emulsifying agents added that able to mix and stabilize the two phases
well for a very long time. From our experiment, a very short time (3.10 minutes)
is required to separate the two phases in test tube 8 because there is no
emulsifying agents added. In test tube 7 where there is only Tween 80, emulsion
that is formed is not stable as it contains shorter separation phase time
(28.22 minutes). This shows that a combination of surfactants can give much
better emulsifying effect than they are used alone.
The time taken for test
tube 3-6 is between >1h25minutes and >1h30minutes. However, test tube 1
and 2 show the most stable emulsion, which have a phase separation time of
>2h. The longer time for test tube 1 can also be explained by the
hydrophobicity of span 20. Span 20 has a more hydrophobic character and a
higher concentration of span 20 in test tube 1 makes it to have a longer
separation time compared to the other test tube which has a lower amount of
span 20.
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.
Tubes
Color
dispersion
Size
droplets
1
More difficult
to spread
Almost size is
same, near to each other, and evenly distributed
2
More difficult
to spread
Almost size is
same, near to each other, and evenly distributed
3
Difficult to
spread
Almost size is
same, near to each other, and evenly distributed
4
Difficult to
spread
Mostly in same
size, and near to each other
5
Slight easy to
spread
Mostly in same
size, and near to each other
6
Easy to spread
Mostly in same
size, and near to each other
7
More easier to
spread
Most is bigger
in size, far from each other, but not uniformly distributed
8
More easier to
spread
The size is
irregular and the distance more far apart from each other
Before
homogenization
After homogenization
Texture: coarse
Texture: smooth
Consistency: less consistent
Consistency: more consistent
Dispersion: poor dispersion
Dispersion: good dispersion
Oily degree: more greasy
Oily degree: less greasy
Globule size: large
Globule size: small
3. Plot and explain:
Mineral oil (ml)
Viscosity average (cP) x
± SD
Difference in viscosity
(%)
Before
After
20
18.93 ±2.0422
19.30±3.9800
1.95 ± 64.36
25
1360±519.81
1180±61.64
14.17±157.60
30
3020± 96.44
6250±984.53
69.69±164.31
35
3290±17.32
13010±1326.91
119.26±194.85
Based on the graph of sample
viscosity before and after temperature cycle versus different amount of mineral
oil plotted above, there are different of viscosity of the emulsions which
formed when using different volume of the mineral oil.
The linear curve of before
temperature cycle shows that viscosity of emulsion which added with 35ml
mineral oil is higher than the emulsion which added with 20ml, 25ml and 30ml of
mineral oil. The linear curve of after temperature cycle also shows that the
emulsion with higher amount of mineral oil (35ml) is more viscous if compared
to the emulsion of lower amount of mineral oil (20ml, 25ml and 30ml). It is
also obvious that the viscosity average all emulsions after the temperature
cycle is higher than before the temperature cycle except for emulsion with 25ml
where the viscosity before temperature cycle is higher than after the
temperature cycle. It is shows that the viscosity average of the emulsion with
35ml mineral oil increased significantly rather than emulsion with 20ml mineral
oil that only increased slightly. The emulsion with 30ml mineral oil also shows
great increase in viscosity if compared to emulsion with 20ml but yet lower
than emulsion with 35ml emulsion. However, emulsion with 25ml is slightly
decrease
Theoretically, an oil in water
emulsion will stabilized by non-ionic emulsifying agents and will undergo phase
inversion and invert to form a water in oil emulsion. This inversion occurs
under a well-defined condition, such as a change in emulsifier solubility which
caused by temperature effects/special interactions with other additives. During
temperature cycle, an increase in temperature cause decrease in viscosity due
to the increase fluidity of the emulsion. Therefore, HLB value of non-ionic
surfactant decrease as it becomes more hydrophobic. In this case, non-ionic
surfactant refers to mineral oil which used in emulsion formulation.
As temperature increased, emulsions
invert until reach phase inversion temperature, where the temperature of
emulsifying agent is equal hydrophilic and hydrophobic tendencies. An increased
temperature will cause a fall in apparent viscosity of continuous phase and
increased kinetic motion of disperse droplets and emulsifying agent at oil in
water interface. At low temperature, the viscosity of continuous phase will be
increased and also the kinetic energy of the system will be reduced. This will
reduces the rate of migration of the globules in the disperse phase. Thus, the
viscosity of the emulsion should be increases after the temperature cycle.
Hence, the higher viscosity average of emulsion obtained after the temperature
cycle can be explained by the formation of water in oil emulsion after the
inversion process. This is because the water in oil emulsion often has higher
viscosity rather than oil in water emulsion.
(ii) Graph of viscosity difference
(%) versus different amount of oil.
The graph of viscosity difference of different emulsions (%) against
volume of mineral oil plotted above show that the percentage of viscosity
difference before and after the temperature cycle increased with the increased
amount of mineral oil used in the formulation. The graph obeyed the theory that
the viscosity differences before and after temperature cycle is increased as
the amount of mineral oil used is increased. The apparent viscosity of the
product increases as concentration of dispersed phase increases. It
means when the amount of oil globules increase in continuous phase, the
viscosity of the emulsion will increase as the viscosity approaches that oil
continuous phase. Therefore the graph obtained have an increasing curve.
APPARATUS
8 tests tube
50ml measuring cylinder
Pasture pipette
and dropper
Vortex mixture
machine
Weighing boats
1 set of mortar
& pestle
Light microscope, Slide
microscope
1 set of 5ml
pipette and bulb
A 50ml beaker
A 15ml centrifugal
tube
Coulter counter
machine
Centrifugator
Water bath (45oC)
Freezer (4oC)
MATERIALS
Palm Oil
Arachis oil
Olive oil
Mineral oil
Span 20, Tween 80
Sudan III solution
(0.5%)
ISOTON III
solution
Distilled water
PROCEDURES
1. 8 tests tube is labeled and 1cm
from the bottom is marked at the tests tube.
2. 4ml of oil (referred to table)
and 4ml of distilled water is mixed in the test tube.
Group
|
Type of oils
|
1,2
|
Palm oil
|
3,4
|
Arachis oil
|
5,6
|
Olive oil
|
7,8
|
Mineral oil
|
3. Span 20 and Tween 80 is added
to the mixture according to the amount given
in the table below. The mixture is mixed using the Vortex mixing machine for
about 45 seconds. The time taken for separation to occur until it reaches the 1cm
marked is recorded. The HLB value for each sample is determined.
in the table below. The mixture is mixed using the Vortex mixing machine for
about 45 seconds. The time taken for separation to occur until it reaches the 1cm
marked is recorded. The HLB value for each sample is determined.
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
|
9.67
|
10.73
|
11.34
|
12.44
|
13.17
|
14.09
|
15.00
|
0.00
|
Phase separation time
(min)
|
>2h
|
>2h
|
>1h30min
|
>1h25min
|
>1h30min
|
>1h25min
|
28.22
|
3.10
|
Stability
|
Most
stable
|
Most
stable
|
More
stable
|
Stable
|
More
stable
|
Stable
|
Not
stable
|
Not stable
|
4. A
few drops of the Sudan III mixture is dropped into 1g
of each of the emulsion formed in the weighing boats. The color dispersion is
described and compared with other emulsion formulation. The emulsion is
observed under the light microscope. The structure and globule size are
determined and drawn to compare with other emulsion.
5. Using wet gum method, Mineral
Oil Emulsion (50g) is prepared using formulation below.
Mineral oil
|
Referred Table III
|
Acacia
|
6.25g
|
Syrup BP
|
5ml
|
Vanillin
|
2g
|
95% Ethanol
|
3ml
|
Distilled water
|
qs 50ml
|
Emulsion
|
Group
|
Mineral oil (ml)
|
I
|
1,2
|
20
|
II
|
3,4
|
25
|
III
|
5,6
|
30
|
IV
|
7,8
|
35
|
6. 40g emulsion formed is placed
in beaker and homogenize 2min using
homogenizer machine.
homogenizer machine.
7. 2g of sample before and after
been homogenized is taken out and placed in
weighing boats and labeled. Sudan III solution is dropped into emulsion. Texture,
consistency, appearance of oil and color dispersion is determined, and compared
and observed under light microscope.
weighing boats and labeled. Sudan III solution is dropped into emulsion. Texture,
consistency, appearance of oil and color dispersion is determined, and compared
and observed under light microscope.
8. 15g of the emulsion that have
been homogenized is taken and the viscosity is
determined using the viscometer that has been calibrated using the “Spindle” LV-4
type. The sample is placed at 45oC (water bath) for about 30 minutes and at 4oC
(freezer) for 30 minutes afterward. The sample that has been exposed to
temperature cycle is then allowed to reach room temperature (10-15minutes). The
viscosity is determined afterward.
determined using the viscometer that has been calibrated using the “Spindle” LV-4
type. The sample is placed at 45oC (water bath) for about 30 minutes and at 4oC
(freezer) for 30 minutes afterward. The sample that has been exposed to
temperature cycle is then allowed to reach room temperature (10-15minutes). The
viscosity is determined afterward.
For 20 ml of mineral
oil:
Reading
|
Viscosity (cP)
|
Average + SD
|
||
1
|
2
|
3
|
||
Before temperature cycle
|
18.9
|
20.7
|
17.2
|
18.93 + 2.0422
|
After temperature cycle
|
18.2
|
22.1
|
17.6
|
19.30 + 3.9800
|
Difference (%)
|
1.95%
|
|||
9. 5g of the emulsion that has
been homogenized is placed into centrifuge tube
and is centrifuged in 4500rpm, for 10 minutes at 25oC. The separation height
produced is measured and the ratio of separation height is determined.
and is centrifuged in 4500rpm, for 10 minutes at 25oC. The separation height
produced is measured and the ratio of separation height is determined.
For 20 ml of mineral oil :
Height (mm)
|
|
Separation phase
|
2.6
|
Initial emulsion
|
5.6
|
Ratio of height
|
0.57
|
CALCULATION
Calculation of HLB values:
Ø HLB value for Span 20 =
8.6
Ø HLB value for Tween 80 =
15.0
RESULTS AND DISCUSSION
1. What are the HLB values to form a stabile emulsion? Discuss.
The HLB value is an indication of the
solubility of the surfactant where the lower the HLB value, the more lipophilic
or oil soluble the surfactant is and the higher the HLB value, the more water
soluble or hydrophilic the surfactant is. Emulsifiers with HLB values ranging
from 3 to 6 will produce water-in-oil emulsions which are stable. On the other
hand, in order to produce oil-in-water emulsions which are stable, emulsifiers
with HLB values ranging from 8 to 18 should be used. For the HLB value between
7-9, emulsifying agents normally act as wetting agent, while between 13-15,
they act as detergents, and value of 15-16, they are become solubilizing agent.
The HLB value for each tube increase
from tube 1 to tube 7. For this experiment, we had use Span 20 and Tween 80 as
the surfactants in the emulsion. A surfactant is used to stabilize both the oil
and aqueous phase which are immiscible. They act by reducing the surface
tension and decreasing the coalescence of dispersed droplets in the emulsion
formed. Hence, the phase separation will occur more slowly. Span 20 has HLB
value of 8.6 while tween 80 has HLB value of 15.
We can determine the stability of an
emulsion more easily from the separation phase time. Emulsion which has the
longest separation phase time is the most stable emulsion. A stable emulsion
contains emulsifying agents added that able to mix and stabilize the two phases
well for a very long time. From our experiment, a very short time (3.10 minutes)
is required to separate the two phases in test tube 8 because there is no
emulsifying agents added. In test tube 7 where there is only Tween 80, emulsion
that is formed is not stable as it contains shorter separation phase time
(28.22 minutes). This shows that a combination of surfactants can give much
better emulsifying effect than they are used alone.
The time taken for test
tube 3-6 is between >1h25minutes and >1h30minutes. However, test tube 1
and 2 show the most stable emulsion, which have a phase separation time of
>2h. The longer time for test tube 1 can also be explained by the
hydrophobicity of span 20. Span 20 has a more hydrophobic character and a
higher concentration of span 20 in test tube 1 makes it to have a longer
separation time compared to the other test tube which has a lower amount of
span 20.
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.
Tubes
|
Color
dispersion
|
Size
droplets
|
1
|
More difficult
to spread
|
Almost size is
same, near to each other, and evenly distributed
|
2
|
More difficult
to spread
|
Almost size is
same, near to each other, and evenly distributed
|
3
|
Difficult to
spread
|
Almost size is
same, near to each other, and evenly distributed
|
4
|
Difficult to
spread
|
Mostly in same
size, and near to each other
|
5
|
Slight easy to
spread
|
Mostly in same
size, and near to each other
|
6
|
Easy to spread
|
Mostly in same
size, and near to each other
|
7
|
More easier to
spread
|
Most is bigger
in size, far from each other, but not uniformly distributed
|
8
|
More easier to
spread
|
The size is
irregular and the distance more far apart from each other
|
Before
homogenization
|
After homogenization
|
|||
Texture: coarse
|
Texture: smooth
|
|||
Consistency: less consistent
|
Consistency: more consistent
|
|||
Dispersion: poor dispersion
(Colour
dispersion: Uneven colour distribution)
|
Dispersion: good dispersion
(Colour
dispersion: Easily and evenly distributed)
|
|||
Oily degree: more greasy
|
Oily degree: less greasy
|
|||
Globule size: large
|
Globule size: small
|
3. Plot and explain:
(i) Graph of sample viscosity before
and after temperature cycle versus different amount of Mineral Oil.
Mineral oil (ml)
|
Viscosity average (cP) x
± SD
|
Difference in viscosity
(%)
|
|
Before
|
After
|
||
20
|
18.93 ±2.0422
|
19.30±3.9800
|
1.95 ± 64.36
|
25
|
1360±519.81
|
1180±61.64
|
14.17±157.60
|
30
|
3020± 96.44
|
6250±984.53
|
69.69±164.31
|
35
|
3290±17.32
|
13010±1326.91
|
119.26±194.85
|
Based on the graph of sample
viscosity before and after temperature cycle versus different amount of mineral
oil plotted above, there are different of viscosity of the emulsions which
formed when using different volume of the mineral oil.
The linear curve of before
temperature cycle shows that viscosity of emulsion which added with 35ml
mineral oil is higher than the emulsion which added with 20ml, 25ml and 30ml of
mineral oil. The linear curve of after temperature cycle also shows that the
emulsion with higher amount of mineral oil (35ml) is more viscous if compared
to the emulsion of lower amount of mineral oil (20ml, 25ml and 30ml). It is
also obvious that the viscosity average all emulsions after the temperature
cycle is higher than before the temperature cycle except for emulsion with 25ml
where the viscosity before temperature cycle is higher than after the
temperature cycle. It is shows that the viscosity average of the emulsion with
35ml mineral oil increased significantly rather than emulsion with 20ml mineral
oil that only increased slightly. The emulsion with 30ml mineral oil also shows
great increase in viscosity if compared to emulsion with 20ml but yet lower
than emulsion with 35ml emulsion. However, emulsion with 25ml is slightly
decrease
Theoretically, an oil in water
emulsion will stabilized by non-ionic emulsifying agents and will undergo phase
inversion and invert to form a water in oil emulsion. This inversion occurs
under a well-defined condition, such as a change in emulsifier solubility which
caused by temperature effects/special interactions with other additives. During
temperature cycle, an increase in temperature cause decrease in viscosity due
to the increase fluidity of the emulsion. Therefore, HLB value of non-ionic
surfactant decrease as it becomes more hydrophobic. In this case, non-ionic
surfactant refers to mineral oil which used in emulsion formulation.
As temperature increased, emulsions
invert until reach phase inversion temperature, where the temperature of
emulsifying agent is equal hydrophilic and hydrophobic tendencies. An increased
temperature will cause a fall in apparent viscosity of continuous phase and
increased kinetic motion of disperse droplets and emulsifying agent at oil in
water interface. At low temperature, the viscosity of continuous phase will be
increased and also the kinetic energy of the system will be reduced. This will
reduces the rate of migration of the globules in the disperse phase. Thus, the
viscosity of the emulsion should be increases after the temperature cycle.
Hence, the higher viscosity average of emulsion obtained after the temperature
cycle can be explained by the formation of water in oil emulsion after the
inversion process. This is because the water in oil emulsion often has higher
viscosity rather than oil in water emulsion.
(ii) Graph of viscosity difference
(%) versus different amount of oil.
The graph of viscosity difference of different emulsions (%) against
volume of mineral oil plotted above show that the percentage of viscosity
difference before and after the temperature cycle increased with the increased
amount of mineral oil used in the formulation. The graph obeyed the theory that
the viscosity differences before and after temperature cycle is increased as
the amount of mineral oil used is increased. The apparent viscosity of the
product increases as concentration of dispersed phase increases. It
means when the amount of oil globules increase in continuous phase, the
viscosity of the emulsion will increase as the viscosity approaches that oil
continuous phase. Therefore the graph obtained have an increasing curve.
4. Plot a graph of ratio of separation phase against different amount
of mineral oil. Discuss.
Mineral Oil (ml)
|
Group
|
Separation phase (mm)
|
Initial emulsion (mm)
|
Ratio of Separation Phase
|
Average Ratio
(Average ± SD)
|
Emulsion I (20mL)
|
1
|
1.8
|
4.4
|
0.41
|
0.49 ±
0.08
|
2
|
2.6
|
4.6
|
0.57
|
||
Emulsion II (25mL)
|
3
|
3.4
|
5.0
|
0.68
|
0.61 ±
0.07
|
4
|
2.7
|
5
|
0.54
|
||
Emulsion III (30mL)
|
5
|
1.5
|
7
|
0.21
|
0.375
± 0.165
|
6
|
27
|
50
|
0.54
|
||
Emulsion IV (35mL)
|
7
|
12.6
|
43
|
0.29
|
0.295
± 0.005
|
8
|
14
|
46
|
0.30
|
Theoretically, the ratio of separation phase will increase when the
amount of oil used increases. This is because as the amount of oil increases,
it exceeds the amount of oily phase which will then affect the formation of
stable emulsion. So, more separation will be resulted.
However, based on the graph plotted, the ratio of separation phase slightly
increases but drop drastically as the amount of mineral oil used increases.
Hence, we can conclude that our results are not accurate due to errors occurred
during experiment. The emulsion produced by using 25 mL of mineral oil supposed
to have a lower ratio of separation phase compare to the 35 mL. However, it
showed a highest ratio of separation phase instead of a lower ratio of separation
phase. The situation is same in emulsions formed by using 20 mL and 30 mL of
mineral oils. These errors may be due to the method of preparation of emulsion,
that is, the wet gum method. May be some of the groups failed to produce good
emulsions. This will definitely affect the stability of emulsion which will
then affect the result of the experiment.
Centrifuge is used to separate an emulsion into its aqueous phase and
oily phase. After the centrifugation, the oily phase is above the aqueous phase.
Ratio of separation phase indicates the stability of an emulsion. The higher
the ratio of separation phase, the lower the stability of the emulsion.
Therefore, a stable emulsion will have a low ratio of separation phase.
Compared to a non-homogenous emulsion, a homogenous emulsion will not separate
easily.
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 which used to increase the viscosity among the interphase of the oily and aqueous phase. Since water and oil cannot mix, acacia acts as a ‘gum’ to bind the water and oil molecule together so that they can mix. Acacia will form a thick film at oil-ater interface to act as barrier to coalescence.As we all know that acacia is a natural product, this may cause it become a good medium for the microbial growth. Thus, agent antimicrobial such as benzoic acid 0.1% is added to stabilize the emulsion from microbial growth. It is different from the surfactant which reduce the surface tension.
Vanillin acts as flavoring agent which increases the taste of emulsion and be more accepted by patients.
Syrup acts as sweetening agent to mask the non-palatable taste of the mineral oil in order to increase patients’ compliance. Syrup may also acts viscosity-enhancing agents to increase the viscosity of the emulsion and ease of pour ability. However, we should take into account the quantity of syrup being used. The quantity of syrup is limited to avoid rheological problem and physical properties of the emulsion. This is to avoid the rheological problem in which the emulsion is maybe hard to pour out from the container and some of it may remain and form a layer surrounding the container wall.
Alcohol is preservative which used to prevent microbial growth because of the presence
of water, syrup and acacia which may enhance the development of microorganism in the oil in this emulsion.
of water, syrup and acacia which may enhance the development of microorganism in the oil in this emulsion.
Distilled water function as aqueous phase (continuous phase) in oil-in-water emulsion.
Mineral oil form the dispersed phase in the oil in water emulsion (o/w emulsion). Some of the oil been used are different in color and this may give rise to different coloration of the emulsion we obtained. Furthermore, the oil such as palm oil has anti-oxidant properties which increase the chemical stability of the emulsion. By the way , if increase the quantity of oil exceed the quantity of water in aqueous phase will cause phase inversion. It is also the same for the quantity of water if exceed the quantity of oil will cause the same problem to occur.
In this experiment, the different composition of mineral oil used affects the physical properties and stability of the emulsion. The stable range for disperse phase is 30-60%. If the disperse phase approaches or exceeds 74% phase inversion may occur. Oil in water emulsion will be produced if the amount of distilled water used is in excess compared to the oil used while water in oil emulsion is produced if the amount of oil used is in excess. Viscosity will increase in addition of more dispersed phase up to a certain point. But decrease in stability after that point. Besides ,phase inversion may also occur with addition of substances that can alter the solubility of emulsifying agent. The most stable emulsion is when the contact angle of immersed particles is 90◦.
CONCLUSION
Viscosity of emulsion increases as
amount of mineral oil increases. So, the emulsion’s stability is reduced.
The combination of emulsifying agents
produce a more stable emulsion than the use of single agent.
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