Title
Evaluation
of the effects of different contents of substance used on the characteristics
of an emulsion formulation.
Objectives
1) To determine
the effect of HLB value of the surfactants on the stability of an emulsion.
2) To study the
physical and stability effects on the emulsion formulation as a result of
different
contents of emulsifying agents used.
Introduction
Emulsion is a thermodynamically
unstable system of two phases. It consists of at least two immiscible liquids
in which one of it (internal or dispersed phase) is dispersed homogenously in
another liquid (external or continue phase). Emulsion can be classified into
two types: water in oil emulsion (w/o) and oil in water emulsion (o/w).
Emulsion is stabilized by the addition of emulsifying agents. Emulsifying
agents, on the other hand, are divided into four types, that is (1) hydrophilic
colloid (2) finely divided solid particles (3) surface active agents or
surfactant.
One method, HLB
(hydrophilic-lipophilic balance) method has been used to determine the quantity
and type of surfactant needed to prepare a stable emulsion. Each surfactant, is
given a number in the HLB scale, that is from 1 (lipophilic characteristic) to
20 (hydrophilic characteristic). Usually, combination of two emulsifying agents
is used to produce a more stable emulsion. The HLB value for the combination of
emulsifying agents can be determined using the formula below:
The
objectives of this practical are (1) to determine the effect of HLB value of
the surfactants on the stability of emulsion, and (2) to study the physical and
stability effects on the emulsion formulation as a result of different contents
of emulsifying agents use.
Apparatus and Materials
Apparatus
8 test tubes 1
set of pipette 5 mL and pipette pump
1 measuring
cylinder 50 mL 1
beaker 50 mL
2 sets of pasture
pipettes and droppers 1
centrifugal tube 15 mL
Vortex mixer Coulter
counter machine
Weighing boat Centrifugator
apparatus
1 set of mortar
& pestle Viscometer
apparatus
Light microscope Water
bath (45°C)
Microscopic slides Refrigerator
(4°C)
Materials
Palm oil Span
20
Arachis oil Tween
80
Olive oil Sudan
III solution (0.5%)
Mineral oil
(Turpentine oil) ISOTON
III solution
Distilled water
Procedures
1.
Each test tube is labelled and 1 cm straight line is sketched from the
end of the tube.
2.
4 mL of oil (Table Ι) and 4 mL of distilled water are mixed into a test
tube.
Table 1
Group
|
Tested oil
|
1, 5
2, 6
3, 7
4, 8
|
Palm oil
Arachis oil
Olive oil
Mineral oil
|
3.
Span 20 and Tween 80 are added to the mixture of oil and water (refer
Table II). The test tube is closed with a closure and it is then mixed with a Vortex mixer for 45 seconds. The time
needed for the phase separation to achieve 1 cm line is recorded. The HLB value
for each sample is determined.
Table ΙΙ
Test 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)
|
58.32
|
126.00
|
130.00
|
70.50
|
127.00
|
81.00
|
13.09
|
4.68
|
Stability
|
No
|
Yes
|
Yes
|
No
|
Yes
|
No
|
No
|
No
|
4.
Few drops Sudan III solution are dropped to a small amount (1 g) of the
emulsion produced in the weighing boat and it is then mixed. The colour
dispersion in the sample is elaborated and compared. A small amount of sample is smeared on the microscopic slide and
observed under the light microscope. The shape and globule size observed are
sketched, elaborated and compared.
5.
By using the wet gum method, Mineral Oil Emulsion (50 g) formulation is
prepared using the following formula:
Mineral oil
|
(refer Table III)
|
Acacia
|
6.25 g
|
Syrup
|
5 ml
|
Vanillin
|
2 g
|
Alcohol (95% ethanol)
|
3 ml
|
Distilled water, qs
|
50 ml
|
Table III
Emulsion
|
Group
|
Mineral oil (mL)
|
I
II
III
IV
|
1,5
2,6
3,7
4,8
|
20
25
30
35
|
6.
40 g of the emulsion produced is poured into a 50 mL beaker and
homogenization process is carried out for 2 minutes using a homogenizer
apparatus.
7.
A small amount of emulsion produced (2g) is placed (before and after
homogenization) into the weighing boat and labeled. A few drops of Sudan III
solution are dropped into the emulsion and it is then mixed. The texture,
consistency, degree of greasiness, shape and colour dispersion of the sample
under the light microscope are elaborated and compared.
8.
The viscosity of the emulsion (15 g in 50 mL beaker) produced after
homogenization is determined using a viscometer which has been calibrated with spindle type
LV-4. Then, the sample is exposed to a temperature of 45°C (water bath) for 30 minutes and then is exposed to a
temperature of 4°C (refrigerator) for 30 minutes. The viscosity
of the emulsion is determined after the exposure to the temperature cycle has
completed and the emulsion achieved room temperature (10 – 15 minutes).
9.
5 g of homogenized emulsion is placed into a centrifugal tube and
centrifuged (4500 rpm, 10 minutes, 25°C). The height of the separation formed is
measured and separation height ratio is determined.
Results
Phase
separation
Time
( minutes )
-Arachis
oil
|
Did
not reach interphase after 120 minutes
|
85.00
|
114.00
|
63.50
|
39.50
|
23.50
|
49.50
|
1.17
|
Phase
separation
Time
( minutes )
-Olive
oil
|
39.50
|
Did
not reach interphase after 120 minutes
|
84.00
|
47.00
|
57.50
|
32.50
|
27.50
|
2.90
|
Phase
separation
Time
( minutes )
-Mineral
Oil
|
Did
not reach interphase after 120 minutes
|
Did
not reach interphase after 120 minutes
|
Did
not reach interphase after 120 minutes
|
97.50
|
59.50
|
43.50
|
11.50
|
2.00
|
'"
HLB value for Span 20 = 8.6
HLB value for Tween 80 = 15.0
Using the formula,
HLB value for Tube 1 = (15
x 8.6) + (3 x 15.0)
(15 + 3)
= 9.67
HLB value for Tube 2 = (12
x 8.6) + (6 x 15.0)
(12 + 6)
= 10.73
HLB value for Tube 3 = (12
x 8.6) + (9 x 15.0)
(12 + 9)
= 11.34
HLB value for Tube 4 = (6
x 8.6) + (9 x 15.0)
(6 + 9)
= 12.44
HLB value for Tube 5 = (6
x 8.6) + (15 x 15.0)
(6 + 15)
= 13.17
HLB value for Tube 6 = (3
x 8.6) + (18 x 15.0)
(3 + 18)
= 14.09
HLB value for Tube 7 = (0
x 8.6) + (15 x 15.0)
(0 + 15)
= 15
HLB value for Tube 8 = (0
x 8.6) + (0 x 15.0)
(0 + 0)
= 0
Palm Oil
Reading
|
Viscosity (cP)
|
Average + SD
|
||
1
|
2
|
3
|
||
Before temperature cycle
|
20
|
20
|
30
|
23.33 + 4.71 = 28.04
|
After temperature cycle
|
10
|
10
|
15
|
11.67 + 2.36 = 14.03
|
Differences (%)
|
49.96%
|
|||
Arachis Oil
Reading
|
Viscosity (cP)
|
Average + SD
|
||
1
|
2
|
3
|
||
Before temperature cycle
|
50
|
50
|
50
|
50 + 0 = 50
|
After temperature cycle
|
100
|
100
|
100
|
100 + 0 = 100
|
Differences (%)
|
100%
|
|||
Olive Oil
Reading
|
Viscosity (cP)
|
Average + SD
|
||
1
|
2
|
3
|
||
Before temperature cycle
|
450
|
500
|
550
|
500 + 40.82 = 540.82
|
After temperature cycle
|
3000
|
2500
|
2350
|
2616.67 + 277.89 = 2894.56
|
Differences (%)
|
435.22%
|
|||
Mineral Oil
Reading
|
Viscosity (cP)
|
Average + SD
|
||
1
|
2
|
3
|
||
Before temperature cycle
|
8900
|
8900
|
8980
|
8926.67 + 37.71 = 8964.38
|
After temperature cycle
|
15650
|
15600
|
15100
|
15450 + 248.33 = 15698.33
|
Differences (%)
|
75.12%
|
|||
Type
of oil
|
Separation
Phase
(mm) |
Original
emulsion
(mm) |
Ratio
|
Palm
Oil
|
35
|
55
|
0.64
|
40
|
50
|
0.80
|
|
Arachis
Oil
|
35
|
50
|
0.70
|
33
|
46
|
0.72
|
|
Olive
Oil
|
22
|
50
|
0.44
|
18
|
50
|
0.36
|
|
Mineral
Oil
|
15
|
55
|
0.27
|
11
|
50
|
0.22
|
Types
of oil
|
Height
Ratio
|
Mean
(
 ) |
Standard
Deviation
(
 ) |
|
Palm
Oil
|
0.64
|
0.80
|
0.72
|
0.113
|
Arachis
Oil
|
0.70
|
0.72
|
0.71
|
0.014
|
Olive
Oil
|
0.44
|
0.36
|
0.40
|
0.057
|
Mineral
Oil
|
0.27
|
0.25
|
0.25
|
0.036
|
Formula of Standard Deviation :
Palm Oil
Arachis
Oil
Olive Oil
Mineral Oil
Discussions
From the results obtained,
the most stable emulsion made from palm oil has a HLB value of 11.34. HLB values for arachis
oil and olive oil to produce the most stable emulsion are 9.67 and 10.73
respectively. As for emulsion containing mineral oil, the range of HLB values
to produce a stable emulsion is from 9.67 to 11.34. Each type of oil used will
need a surfactant of a particular HLB value in order to produce a stable
product.
Emulsion in test tube 8 for all types of oil is the least stable.
Yellowish oil phase floats above water phase as oil is less dense than water.
Phase separation occurs in the shortest time. This is because no surfactant
(Span 20 or Tween 80) is added into the emulsion.
In test tube 7, only Tween 80 is added into the emulsion. The emulsion
is not stable because phase separation occurs faster compared to other emulsion
which have two surfactants. Combination of different surfactant in a correct
amount would produce a stable emulsion.
Surfactants act to reduce the interfacial tension between oil phase and
aqueous phase by forming a barrier between the two phases. Optimum HLB is
necessary to allow the surfactant to be present at the interphase. Surfactants
contain polar and non-polar region. The non-polar, hydrocarbon chain is
hydrophobic. This region will attempt to stay away from the aqueous phase.
Thus, it will accumulate at the interphase. Adsorption of surfactant at the
interphase would reduce interfacial tension. Lower interfacial tension is
thermodynamically favoured. Surfactants would decrease the tendency for
interface to contract and reduce coalescence. Thus, surfactants increase stability
of emulsion. When surfactants are added to emulsion, it will cause a reducrion
in mean globule diameter. This will increase the apparent viscosity of the
emulsion, leading to a stable emulsion.
Content of mineral oil (ml)
|
Average viscosity
(cP)
|
Differences of viscosity
|
|||
(x ± SD)
|
(%)
|
||||
Before
|
After
|
(x ± SD)
|
|||
temperature cycle
|
temperature cycle
|
||||
20 - palm oil
|
23.33 ±
4.71
|
11.67 ± 2.36
|
49.96%
|
||
25 - arachis oil
|
50 ±
0
|
100 ± 0
|
100%
|
||
30 - olive oil
|
500 ±
40.82
|
2616.67 ± 277.89
|
435.22%
|
||
35 - mineral oil
|
8926.67 ± 37.71
|
15450 ± 248.33
|
75.12%
|
||
aa) Graph
of viscosity of sample before and after the temperature cycle against content
of different mineral oil.
From
the graph above, we can see that the viscosity of mineral oil have the highest
value before and after the the temperature cycle which are 8926.67 cP and 15450
cP respectively. The viscosity for palm
oil and arachis oil cannot be seen in this graph because of greater differences
in value between both palm oil and arachis oil and mineral oil. But from the
table, we can see that palm oil have the lowest viscosity which are 23.33 cP
and 11.67 cP respectively.
The viscosity for each types of
mineral oil were increasing after the temperature cycle except for palm oil. If
the temperature changes enough, the viscosity of oil will change, too. Oil is
designed to resist changes in viscosity with temperature changes. But if the
change of temperature is extreme either it is become more hotter or colder,
then the viscosity also will change. When temperature gets hotter, the
viscosity of oil decreases and when it is gets colder, the viscosity of oil
increases. Viscosity were increases because the droplets of oil tend to
coalesce and this will make it more
viscous. But, the viscosity of palm oil was decrease. This maybe because of
some error while doing the experiment such as error in weighing or measuring
the materials or not using suitable viscometer spindle.
The volume of all types of mineral
oil also will effect the viscosity. We can see from the table that, the volume
of palm oil, arachis oil, olive oil and mineral oil are 20 mL, 25 mL, 30 mL and
35 mL respectively. The viscosity of mineral oil was the highest among others.
This is because increase the volume of
mineral oil will increase the weight and also pressure. This will then,
increase the viscosity of the mineral oil
ab) Graph
of differences in viscosity (%) against content of different oil
From
the graph above, we can see that the value of differences in viscosity in
percentage vary with the content of mineral oil. 20 mL is for palm oil, 25 mL
is for arachis oil, 30 mL and 35 mL are for olive oil and mineral oil
respectively. The differences in
viscosity for olive oil was the highest among others which is 435.22%. This can
be relate with the factors that affecting the viscosity which are size
molecules, shape of molecules and intermolecular forces. Viscosity of sample
having large molecules is high whereas the viscosity of those sample that have
small molecues is low. Spherical molecules provide resistance but oval shaped
or disc like molecules provide greater resistance in the flow of liquid.
Samples having large intermolecular forces have greater viscosity.
c)
Graph
of ratio of separation phase against type of oil
Gravity is mainly
associated with the slow sedimentation process of an immiscible mixture. A
common way to accelerate this sedimentation is by the use of centrifugation,
where the high achievable rotation frequencies permit an effective
acceleration. Separator for different oil.
Oil emulsion is used for this experiment and each of the emulsion is taken for
5g. The emulsion then undergoes the centrifuge process for about 4500rpm, 10
minute at 25°C.
The graph compares between different
types of oil based on the ratio of separation phase. The palm oil gives quite a
huge difference in the ratio, the olive and mineral oil also give a little
differences in the ratio. But, for arachis oil, it gives the least ratio
difference on the graph. As the standard deviation of the arachis oil is the
smallest compared the other three oils. The palm oil shown the largest standard
deviation in the experiment. The height of separation phase indicates the
stability of the emulsion. When the height of phase separation is larger, the
stability of the emulsion is low. The graph shown the palm oil has the highest
separation phase ,so, it might be has the lowest stability among others. The
mineral oil has the least height separation phase, thus it has the highest
stability of emulsion.
The mineral oil has the highest
stability when the viscosity of the emulsion is high. As the volume of oil used
is high, the viscosity also will be high. Type of oil also plays a role in
determining the stability of the emulsion.
a d) Function
of each material used in the emulsion formulation and how does this different
type of material affect the physical characteristics and stability of the
emulsion.
Span 20 and Tween 80 act as emulsifying
agent. They both have different HLB value. The number of drops of both
emulsifying agent affect their value of HLB. The HLB of an emulsifier is an
expression of its Hydrophile-Lipophile Balance, the balance of the size and
strength of the hydrophilic and lipohilic groups of the emulsifier. All
emulsifiers consist of a molecule that combines both hydrophilic and lipophilic
groups. In this experiment, the emulsifier used are Span 20 which are
lipophilic as the HLB value is below than 10 and Tween 80 which are hydrophilic
with HLB value greater than 10. The HLB of an emulsifier is related to its
solubility. Thus, an emulsifier having low HLB will tend to be oil-soluble, and
one having a high HLB will tend to be water-soluble. The number of drops of the
emulsifiers mixed with the oil determine the value of the HLB. The value of HLB
then determines the stability of the emulsion. A blend of emulsifiers having an
HLB of 10 will make a more stable fluid oil in water emulsion than emulsifiers
of any other HLB value.
Sudan III is used to
determine the type of emulsion. Red dyes soluble in the oil but not in the
water. A small portion of the finely powdered dye is dusted over the surface of
the emulsion. If oil is the external phase the color gradually spreads
throughout the emulsion. But if water is the external phase the color does not
spread but is confined to the oil with which it comes in contact on the
surface. The microscope may be used to determine the type of emulsion formed.
If the oil is dyed red, a red field with clear globules indicates a
water-in-oil emulsion; red globules in a clear field show an oil-in-water
emulsion.
Acacia which is being
added into the emulsion act as emulsion stabilizers by making coherent
multi-molecular film. This film is strong and resists coalescence. They have
also an auxiliary effect by increasing the viscosity of the dispersion medium.
It can also provide electrostatic repulsion.
Conclusion
Different amount of HLB
value of the surfactant added into the formulation affect the stability of the
emulsion and its separation time. Span 20 and Tween 80 which are the
emulsifying agent having different value of HLB help to improve the stability
and physical characteristics of the emulsion.
References
1. Aulton,
M.E. 2002. Pharmaceutics: The science of dosage form design. Edinburgh:
Churchill Livingstone
2. Banker,
G.S. & Rhodes, C.T. 1990. Modern pharmaceutics. 2nd Ed. New
York: Marcel Dekker.
3. Florence,
A.T. & Attwood, D. 1998. Physico-chemical principles of pharmacy. 3rd
Ed. New York: Macmillan.
4.
http://wiki.answers.com/Q/Does_an_increase_or_decrease_in_temperature_affect_the_viscosity_of_oil
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