OBJECTIVES
To determine:
1. The effects of HLB
surfactant on the stability of the emulsion.
2. The effects of
different oil phases used in the formulation on the physical characteristics
and stability of the emulsion.
INTRODUCTION
An emulsion is a
colloid of two or more immiscible liquids where one liquid contains a
dispersion of the other liquids and an emulsifying agent. It is
thermodynamically unstable two-phase system. The dispersed liquid is known as
the internal or discontinuous phase, whereas the dispersion medium is known as
the external or continuous phase. In general there are two types of emulsion
which are oil-in-water (o/w) emulsion and water-in-oil (w/o) emulsion. An o/w
emulsion is generally formed if the aqueous phase constitutes > 45% of the
total weight, and a hydrophilic emulsifier is used while w/o emulsions are
generally formed if the aqueous phase constitutes < 45% of the total weight
and a lipophilic emulsifier is used.
Emulsions are used
in many routes of administration. Oral administration can be used, but patients
generally object to the oily feel of emulsions in the mouth. But sometimes,
emulsions are the formulation of choice to mask the taste of a very bitter drug
or when the oral solubility or bioavailability of a drug is to be dramatically
increased.
More typically,
emulsions are used for topical administration. Topical emulsions are creams
which have emollient properties. They can be either o/w or w/o and are
generally opaque, thick liquids or soft solids. Emulsions are also the bases
used in lotions, as are suspensions. The term “lotion” is not an official term,
but is most often used to describe fluid liquids intended for topical use.
Lotions have a lubricating effect. They are intended to be used in areas where
the skin rubs against itself such as between the fingers, thighs, and under the
arms. Emulsions are also used
an ointment bases and intravenously administered as part of parenteral
nutrition therapy.
Emulsion is
stabilized by adding emulsifying agent. The HLB method (hydrophilic-lipophilic
balance) is used to determine the quantity and type of surfactant that is
needed to prepare a stable emulsion. Every surfactant is given a number in the
HLB scale, that is, from 1 (lipophilic) to 20 (hydrophilic). Usually a
combination of two emulsifying agent is used to form a more stable emulsion.
HLB value for a combination of emulsifying agents can be determined by using
the following formula:
 |
APPARATUS
8 Test tubes
1 set of 5ml pipette and bulb
A 50ml measuring
cylinder 1 50ml beaker
2 sets of pasture
pipettes and droppers 15ml centrifugation tube
Vortex mixer Centrifugation
apparatus
Weighing boat
Viscometer
1 set of mortar
and pestle Water
bath (45°C)
Light
microscope
Refrigerator (4°C)
Microscope
slides
MATERIALS
Palm oil
Span 20
Arachis oil
Tween 80
Olive oil
Sudan III solution (0.5%)
Mineral oil
Distilled water
PROCEDURES
1. Each test tube was labeled and marked 1cm
from the base of the test tube.
2. 4ml of mineral oil was mixed with 4ml of distilled
water into the test tube.
3. Span 20 and tween 80 were added into the
mixture of oil and water (refer table 1). Then the test tube is closed and
mixed its content with vortex mixer for 45 seconds. The time needed for the
interface to reach 1cm was recorded. The HLB value for each sample was
determined. Step 1-3 were repeated in order to obtain an average HLB value of a
duplicate.
4. A few drops of Sudan III solutions were
added to (1g) emulsion formed in a weighing boat and mixed homogenously. The
spread of the color in the sample were compared. Spread some of the sample on a
microscope slide and it was observed under light microscope. The appearance and
globule size formed were drew and described.
RESULT
PALM OIL (GROUP 1 & 5)
Tube No.
|
Span
20
(Drops)
|
Tween
80
(Drops)
|
HLB
Value
|
Time For Phase Separation (min)
|
Spreading of Sudan
III solution
|
||
T1
|
T2
|
Average
|
|||||
1
|
15
|
3
|
9.66
|
47.38
|
45.34
|
46.36
|
Sudan III colour
dispersed in the emulsion.
|
2
|
12
|
6
|
10.73
|
45.36
|
44.34
|
45.25
|
Sudan III colour
dispersed in the
emulsion.
|
3
|
12
|
9
|
11.34
|
34.16
|
29.54
|
32.25
|
Sudan III colour
dispersed in the emulsion.
|
4
|
6
|
9
|
12.44
|
37.15
|
39.00
|
38.08
|
Sudan III colour
dispersed in the emulsion,
|
5
|
6
|
15
|
13.17
|
30.45
|
33.27
|
32.26
|
Sudan III colour
dispersed in the emulsion.
|
6
|
3
|
18
|
14.08
|
23.01
|
20.47
|
23.54
|
Sudan III colour
dispersed in the emulsion.
|
7
|
0
|
15
|
15.00
|
10.10
|
12.22
|
11.16
|
Sudan III colour
dispersed in the emulsion
|
8
|
0
|
0
|
0.00
|
3.40
|
5.12
|
4.26
|
Sudan III colour
dispersed in the emulsion
|
ARACHIS OIL (GROUP 2 & 6)
Tube No.
|
Span
20
(Drops)
|
Tween
80
(Drops)
|
HLB
Value
|
Time For Phase Separation (min)
|
Spreading of Sudan III solution
|
||
T1
|
T2
|
Average
|
|||||
1
|
15
|
3
|
9.66
|
47.22
|
43.18
|
45.20
|
Spreading of Sudan
III is not uniform. Large globules are seen.
|
2
|
12
|
6
|
10.73
|
41.58
|
36.96
|
39.27
|
Sudan III spread
rapidly but the
spreading is uneven.
|
3
|
12
|
9
|
11.34
|
40.61
|
34.49
|
37.55
|
Sudan III spread
slowly and evenly.
|
4
|
6
|
9
|
12.44
|
28.47
|
29.11
|
28.79
|
Sudan III spread
uniformly.
Large globules are seen.
|
5
|
6
|
15
|
13.17
|
19.38
|
19.00
|
19.19
|
Sudan III spread evenly.
Globule sizes are relatively uniform.
|
6
|
3
|
18
|
14.08
|
10.69
|
8.25
|
9.47
|
Sudan III spread
unevenly.
Globules are mostly large in size.
|
7
|
0
|
15
|
15.00
|
7.34
|
5.16
|
6.25
|
Spreading is quick. Various sizes of
globules
unevenly distributed.
|
8
|
0
|
0
|
0.00
|
5.12
|
4.94
|
5.03
|
Sudan III did not
disperse in the emulsion.
|
OLIVE OIL (GROUP 3 & 7)
Tube No.
|
Span
20
(Drops)
|
Tween
80
(Drops)
|
HLB
Value
|
Time For Phase Separation (min)
|
Spreading of
Sudan III
solution
|
||
T1
|
T2
|
Average
|
|||||
1
|
15
|
3
|
9.66
|
Interphase does
not reach
1 cm after
150 minutes
|
Interphase does
not reach
1 cm after 150 minutes
|
-
|
Spread very slowly
|
2
|
12
|
6
|
10.73
|
Interphase
does not reach
1 cm after
150 minutes
|
Interphase does not reach
1 cm after 150 minutes
|
-
|
Spread very slowly
|
3
|
12
|
9
|
11.34
|
58.27
|
65.3
|
61.79
|
Spread moderately
|
4
|
6
|
9
|
12.44
|
15.29
|
23.45
|
19.37
|
Spread moderately
|
5
|
6
|
15
|
13.17
|
87.2
|
79.34
|
83.27
|
Spread moderately
|
6
|
3
|
18
|
14.08
|
62.29
|
58.1
|
60.2
|
Spread moderately
|
7
|
0
|
15
|
15.00
|
32.17
|
40.55
|
36.36
|
Spread moderately
|
8
|
0
|
0
|
0.00
|
1.2
|
2.4
|
1.8
|
Spread immediately
|
MINERAL OIL (GROUP 4 & 8)
Tube No.
|
Span
20
(Drops)
|
Tween
80
(Drops)
|
HLB
Value
|
Time For Phase Separation (min)
|
Spreading of Sudan III solution
|
||
T1
|
T2
|
Average
|
|||||
1
|
15
|
3
|
9.66
|
Interphase does not reach
1 cm after
150 minutes
|
Interphase does
not reach
1 cm after
150 minutes
|
-
|
Spread very slowly
|
2
|
12
|
6
|
10.73
|
Interphase does not reach 1 cm after 150 minutes
|
Interphase does
not reach
1 cm after 150 minutes
|
-
|
Spread very slowly
|
3
|
12
|
9
|
11.34
|
110
|
115
|
112.5
|
Spread slowly
|
4
|
6
|
9
|
12.44
|
101.2
|
104.3
|
102.75
|
Spread slowly
|
5
|
6
|
15
|
13.17
|
87.4
|
89.4
|
88.4
|
Spread moderately
|
6
|
3
|
18
|
14.08
|
69.2
|
70.2
|
69.7
|
Spread moderately
|
7
|
0
|
15
|
15.00
|
19.6
|
51.7
|
35.65
|
Spread slowly
|
8
|
0
|
0
|
0.00
|
5.12
|
1.55
|
3.3
|
Spread immediately
|
Tube no.
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Span 20 (drop)
|
15
|
12
|
12
|
6
|
6
|
3
|
0
|
0
|
Tween 80 (drop)
|
3
|
6
|
9
|
9
|
15
|
18
|
15
|
0
|
HLB
value
|
9.66
|
10.73
|
11.34
|
12.44
|
13.17
|
14.08
|
15.00
|
0.00
|
PHYSICAL APPEARANCES ON MINERAL OIL EMULSION
Test tube
|
HLB Value
|
Observation of Sudan III Test (Naked eye)
|
Observation under microscope
|
1
|
9.66
|
Sudan III dispersed very slowly and unevenly
throughout the emulsion, but red dye can be seen
|
Size of globules varies about medium size and
unevenly distributed, small bubbles seen on top
|
2
|
10.73
|
Sudan III dispersed slowly and unevenly throughout
the emulsion, red dye can still be seen
|
Uniform size of small globules evenly distributed,
but only few throughout the emulsion
|
3
|
11.34
|
Sudan III dispersed slowly and unevenly throughout
the emulsion, red dye can still be seen
|
A more uniform smaller size of globules formed
evenly distributed, very small bubbles observed on top
|
4
|
12.44
|
Sudan III dispersed slowly but evenly throughout the
emulsion, red dye can be seen
|
Size of globules varies about small and large size
and unevenly distributed formation
|
5
|
13.17
|
Sudan III dispersed moderately and evenly throughout
the emulsion, red dye can be seen
|
Uniform small size of globules unevenly distributed
throughout the emulsion
|
6
|
14.08
|
Sudan III dispersed moderately and evenly throughout
the emulsion, red dye can be seen
|
Large size of globules unevenly distributed
throughout the emulsion
|
7
|
15.00
|
Sudan III dispersed slowly throughout the emulsion,
red dye can be seen
|
Uniform size of medium globules evenly distributed
throughout the emulsion
|
8
|
0.00
|
Sudan III dispersed immediately throughout the
emulsion, red dye can be seen
|
A few globules formed but dispersions of two media
did not occur due to absence of surfactant
|
 |
| TUBE 1 |
 | ||
TUBE 2
|
 | ||
TUBE 4
|
 |
| TUBE 6 |
 |
| TUBE 7 |
 |
| TUBE 8 |
DISCUSSION
By
nature, emulsions are physically unstable, which eventually separate into
two liquid layers
or phases. Creaming occurs when dispersed oil droplets merge and rise to the
top of an o/w emulsion or settle to the bottom in w/o emulsions. In both cases,
the emulsion can be easily re-dispersed by shaking. Coalescence (breaking or
cracking) is the complete and irreversible separation and fusion of the
dispersed phase. Finally, a phenomenon known as phase inversion or a change
from w/o to o/w (or vice versa) may occur. This is considered a type of
instability by some.
Surfactant functions
as the thickening agent, which increases the viscosity of the suspension or any
aqueous vehicle thus slowing down the rate of sedimentation as per Stoke’s law and simultaneously stabilizing the emulsion by reducing the interfacial tension
and prevent droplets from coalescence and maintain the individual droplets in
the continuous phase. Thereby, no distinct layers are present. It also appears
more cloudy and smooth. Although
emulsifiers help stabilize a mixture of oil and water, emulsions are still inherently
unstable and eventually will separate. The speed at which this occurs depends
on the composition of the emulsion, and the type and concentration of the
emulsifiers. The stability and physical characteristics of emulsion depends on
the HLB value of surfactant used in formulation. HLB value for a combination of
emulsifying agents can be determined by using the following formula :
Surfactant
which is water-soluble and surfactant that is oil-soluble which are combined
together are used to promote the solubility and stability of oil in water or
water in oil system. The combination also yields optimum performance compared
to a single surfactant system. The surfactants used for the emulsion
preparation are non-ionic surfactants which when consumed, will not alter the
ionic balance within the body.
For
example, you will use a water-soluble or hydrophilic emulsifier or blend to
make an o/w emulsion which is when the aqueous phase constitutes > 45% of the total weight as for the
stable phase, or to solubilize oils, or to obtain detergent action. In other
words, you use a water-soluble emulsifier when you want your final product to
exhibit aqueous characteristics, that is dilute readily with water. For these
purposes, you would rarely use an oil-soluble or lipophilic emulsifying system.
On the other hand, if you wanted to make a w/o emulsion which are generally
formed if the aqueous phase constitutes
< 45% of the total weight, or couple water soluble materials into an
oil, or produce some other type of non-aqueous emulsion system, you would
choose an oil-soluble emulsifier.
Recording
the time taken of the oil and water interface to reach 1 cm can be helpful to
determine the required HLB value. As the time taken to reach 1 cm increases,
the better the combination of surfactants used. The longer the time taken for
the emulsion to reach the interface, the greater the stability of the emulsion.
Palm oil has the greatest stability compared to others oil at the same HLB value,
followed by mineral oil, olive oil and arachis oil. In short, the most suitable
HLB value is 11.3, 12.4, 13.2 and 14.1.
Palm
oil, arachis oil, olive oil and mineral oil act as oil phase (internal phase)
in the o/w emulsion. The increasing of oil phase increases the viscosity of the
emulsion which require longer time for phase separation process. Acacia, Span
20 and Tween 80 are emulsifying agents used to emulsify two immiscible liquids
which are liquid and oil into a miscible form and increases the viscosity of
the emulsion, hence stabilize it. Syrup is used as sweetening agent, masking
the unpleasant or non-palatable taste of mineral oil and it is also can
increase the viscosity of the emulsion, only in controlled amount to
prevent too viscous. When the level of internal phase volume increases
and consequently the amount of water as continuous phase decreases, emulsion
viscosity will be increased. The consistency of emulsions’ stability can be
increased by increasing the viscosity of the continuous phase, and also
increasing proportion of emulsifying agents into it.
There
are few precaution steps should be considered during
preparation of microscope slide.
First, always check that the
slide is clean and perfectly transparent
before spreading the emulsion onto it. Second, do not stain the whole
surface of the slide to avoid wastage
and messiness.
Finally, the cover slip should be placed with
extra caution to avoid air bubbles.
CONCLUSION
Different amount
of oil phase also influence the appearance and stability of the emulsion. The stability and
physical characteristics of emulsion depends on the HLB value of surfactant
used in formulation. Surfactant which is water-soluble and surfactant that is
oil-soluble which are combined together are used to promote the solubility and
stability of oil in water or water in oil system. The correct combination yields optimum
performance compared to a single surfactant system.
Emulsion Part II : Homogenisation,
Viscosity and Centrifugation.
Result
Homogenisation:
The
microscopic view of emulsion
Microscopic
view
|
|
 |
 |
Before homogenization
|
After homogenization
|
Emulsion
I
Characteristics
|
Before Homogenisation
|
After Homogenisation
|
Texture
|
Coarse and not
homogenous
|
Smooth and even
looking, homogenous
|
Consistency
|
Less consistent
|
More consistent
|
Degree of Oily
Appearance
|
More oily and globules
|
Less oily and globules
|
Spreading of Colour
|
Spread evenly
|
Spread evenly
|
Emulsion
II
Characteristics
|
Before Homogenisation
|
After Homogenisation
|
Texture
|
Coarse
|
Smooth
|
Consistency
|
Less consistent, more
dilute
|
More consistent, more
vicious
|
Degree of Oily
Appearance
|
More oily, spherical
globules
|
Less oily, spherical globules
|
Spreading of Colour
|
Spread evenly
|
Spread evenly
|
Emulsion
III
Characteristics
|
Before Homogenisation
|
After Homogenisation
|
Texture
|
Coarse, not homogenous,
cloudy
|
Milky, smooth,
homogenous
|
Consistency
|
Not consistent, less
viscous
|
Consistent, more
viscous
|
Degree of Oily
Appearance
|
Greasier, more globules
|
Less greasy, less
globules
|
Spreading of Colour
|
Unevenly dispersed
colour, less red spot
|
Evenly dispersed
colour, more red spot
|
Emulsion
IV
Characteristics
|
Before Homogenisation
|
After Homogenisation
|
Texture
|
Not homogenous, course,
less milky
|
Homogenous, smooth,
more milky
|
Consistency
|
Not consistent, less
viscous
|
Consistent, more
viscous
|
Degree of Oily
Appearance
|
More greasy, more
globules
|
Less greasy, less
globules
|
Spreading of Colour
|
Unevenly distribution
|
Evenly distribution
|
Viscosity
Readings
|
Average viscosity (cP)
|
|||||||
Emulsion I
|
Emulsion II
|
Emulsion III
|
Emulsion IV
|
|||||
Group 1
|
Group 5
|
Group 2
|
Group 6
|
Group 3
|
Group 7
|
Group 4
|
Group 8
|
|
Before temperature
cycle
|
1862
|
368.33
|
1352
|
1312
|
848
|
1312
|
768
|
176
|
After temperature cycle
|
4689
|
608.33
|
1526
|
1309
|
1528
|
1450
|
452
|
196
|
Difference (%)
|
61.06
|
65.22
|
15.17
|
0.23
|
80.19
|
10.52
|
69.91
|
10.2
|
Graph
1.a
Graph
1.b
Graph
2.a
Graph
2.b
Centrifugation
Mineral Oil (ml)
|
Distance of separation
(cm), y
|
Average
|
Ratio of separation
phase = y/x
|
|
20
|
2.7
|
2.9
|
2.80
|
2.80/4.60 = 1.61
|
25
|
2.6
|
4.0
|
3.30
|
3.30/5.00 = 0.66
|
30
|
3.0
|
2.0
|
2.50
|
2.50/4.00 = 0.63
|
35
|
3.7
|
3.2
|
3.45
|
3.45/5.00 = 0.69
|
x
= distance before separation
y
= distance after separation
Discussion
Homogenisation
To
produce oil in water (o/w) emulsion, we used wet gum method. The emulsion
requires several excipients to increase its stability. Acacia acts as a
surfactant to help the internal phase dispersed evenly in the continuous phase.
Besides providing flavouring, syrup also increases the viscosity of the
emulsion and thus helps to prevent the merging of the droplets. Alcohol is an
antimicrobial agent to prolong the storage time of the emulsion. We also added
Sudan III solution which acts as a dye to provide a clearer microscopic view of
droplets of the emulsion.
Firstly, the microscopic view of the
emulsion helps us to observe the texture, consistency, degree of oily
appearance, size of globules and spreading of colour in the emulsion. Before
homogenization, all of the emulsions are greasy because the oil phase and water
phase are not well mixed yet. The purpose
of homogenization is to homogenize the two immiscible liquid into a smooth
emulsion by making the droplets into extremely small particles dispersed evenly
in the continuous phase. Thus, after homogenization, the texture becomes smooth
and homogenous. Its consistency is increased, less greasy and fewer globules
produced. The water and oil phase are mixed in a
well manner and causes the oil globules are completely surrounded by water.
Viscosity
Oil
is more viscous than water. Theoretically, when the amount of mineral oil
increase, the viscosity of the emulsion will increase. From the experiment, in
Graph 1.a, before the temperature cycle, we can see that the viscosity of
emulsions decrease when the amount of mineral oil increase. Meanwhile, for
Graph 1.b, there is a fluctuation occurs at 25ml to 30ml. Based on the result,
for the former, emulsion with 20 ml mineral oils has the highest viscosity
(1862cP), while the latter, emulsions of 25 ml and 30 ml mineral oils top any
other amount of mineral oils with the values of 1312cP. This may be due to some
error during the experiment in producing the emulsions and the use of different
viscometer. Theoretically, the viscosity should have increased from the
emulsion with lowest amount of mineral oil to the highest.
The temperature cycle is used to test the physical
stability of the emulsion by passing through the emulsion to water bath of 45
degree Celsius for 30 minutes and then keep it in the freezer for the next 15
minutes. When the temperature increase, the viscosity of emulsion decrease.
This is due to the oil globules gain more kinetic energy and can collide with
each other more frequently. This may results in coalescence and breaking of the
emulsion. While at low temperature, the kinetic energy of oil globules reduces.
The viscosity of the emulsion will increase and it is harder for the oil
globule to collide with each other and reduces the chances for coalescence.
Hence, emulsion is more stable at low temperature. Thus, after the temperature
cycle, the viscosity of the emulsion increases. Theoretically, the
difference of viscosity is directly proportional to the amount of oil. The
difference should not be too far from the original viscosity. As from the graph
2.a and 2.b, the former shows that the emulsion with 35 ml mineral oils has the
lowest difference and the latter is 25 ml of mineral oils emulsion get the
smallest value. Due to the error in the
experiment, all the emulsions showed increase in the viscosity after
temperature cycle but the increase is not proportional to the amount of mineral
oil.
Centrifugation
Centrifugation is a process that separates liquids
with different densities from each other and solid from liquid. This process is
carried out in a centrifuge. This apparatus rotates at high speed and produce
centripetal force that separates substances with different densities.
In this experiment, we have took 5ml of homogenised
emulsion from the 40g of emulsion that we prepared earlier.. Since water is
much denser compared to oil, thus water will be at the bottom and the oil phase
will be on top after finished centrifugation process. So emulsion with 20ml of
mineral oil should have more aqueous phase compared to emulsion with 25ml, 30ml
and 35ml of mineral oil respectively. Thus theoretically, the separation phase
ratio should be increased with the increased of mineral oil in the formulation
However, the result we obtained does not follow this
theory. These happen maybe due to some experimental errors such as measurement
mistakes and systemic error. The experimental errors include inaccuracy in
measuring the amount of oil before forming the emulsion, insufficient
homogenisation that has been carried out on emulsion and the height of
separated phase is not being measured accurately.
Therefore during preparation of emulsion, there are
some precautions steps need to take note. Firstly, the mixture of acacia
and mineral oil is vigorously and continually triturated until the primary
emulsion formed to ensure the two components are mixed evenly. While
adding the water to the mixture, the water should be added slowly and
triturated with pestle continuously to avoid breakage of the emulsion. Avoid
measurements mistakes as can as possible and transfer the information from
other group carefully.
Conclusion
Based on the experiment, it can be concluded that before homogenization, most of the emulsion is coarse, greasier and less consistent. However, after homogenization, the emulsion became smoother, less oily and effectively consistent. For viscosity, the higher the amount of mineral oil, the higher the viscosity, and the more stable the emulsion is. In addition, centrifugation can be said that the separation phase ratio should be decreased with the increased of mineral oil in the formulation, as it is more stabilised.
References :
1. Collett, D.M. & Aulton, M.E. 1990. Pharmaceutical practice. Ed. ke-3. Edinburgh: Churchill Livingstone.
Based on the experiment, it can be concluded that before homogenization, most of the emulsion is coarse, greasier and less consistent. However, after homogenization, the emulsion became smoother, less oily and effectively consistent. For viscosity, the higher the amount of mineral oil, the higher the viscosity, and the more stable the emulsion is. In addition, centrifugation can be said that the separation phase ratio should be decreased with the increased of mineral oil in the formulation, as it is more stabilised.
References :
1. Collett, D.M. & Aulton, M.E. 1990. Pharmaceutical practice. Ed. ke-3. Edinburgh: Churchill Livingstone.
2. Griffin, W. C. Classification of Surface Active Agents by HLB. J. Soc. Cosmet. Chem. 1949, 1, 311-326.
3. Florence, A.T. & Atwood, D. 2011. Physicochemical Principles of Pharmacy. 4thedition. London: Pharmaceutical Press
3. Florence, A.T. & Atwood, D. 2011. Physicochemical Principles of Pharmacy. 4thedition. London: Pharmaceutical Press
