Title:
Evaluation on the effect of different
ingredient composition to the characteristics of emulsion formulation
Objective:
1)
To determine the effect of HLB
(Hydrophilic-Lipophilic Balance) surfactant on the stability of emulsion.
2)
To
investigate the physical effect and stability on the emulsion as different
amount of emulsifying agent is used.
Date:
12/5/2015
Introduction
Emulsion consists of two different phases that is not thermodynamically
stable. It contains two immiscible liquids. One of them is dispersed as
globules (dispersed phase=internal phase), the other one is continuous phase
(external phase). It can be classified
as oil-in-water (o/w) emulsion or water-in-oil (w/o) emulsion. The droplet size
affects the distribution of dispersed phase of emulsion. For micro emulsion,
the droplets size range 0.01 to 0.1 mm. For macro emulsion, the droplets size
range approximately 5 mm. Emulsion can be stabilized by adding stabilizing
agents. Emulsifying agents can be divided into 3 types, which are hydrophilic
colloid, finely divided solid particles, and surface active agents or
surfactants.
Emulsions are thermodynamically unstable systems. They tend to give
phase separation after force is removed. However, by using appropriate
emulsifying agent the interfacial tension can be decreased, and the stability
of these systems can be significantly increased for the emulsion to stand
mixing. A good emulsion should be stable itself, chemically inert, nontoxic and
cause no irritation upon application, be odourless, tasteless, and colourless
and be inexpensive.
Surfactants can be classified using the HLB system established by
Griffin. This system provides a scale of surfactant hydrophilicity (HLB value
range from 1 to 20 which from most hydrophobicity to hydrophilicity).
Generally, 2 emulsifying agents are usually used to form a stable emulsion
preparation.
HLB method
(hydrophilic-lipophilic balance) was used to determine the quantity and type of
surfactants that will needed to prepare a stable emulsion. Each of surfactants,
will be given a number in HLB scale which is from 1 (lipophilic) until 20
(hydrophlilic). Normally, combination of two emulsifying agents used to produce
an emulsion that is more stable. HLB value for combination of emulsifying
agents can be determined by using the formula as followed:
HLB value =
(Amount of
surfactant 1) (HLB surfactant 1) + (Amount of surfactant 2) (HLB surfactant
2)
Amount
of surfactant 1 + Amount of surfactant
There are 5 issue of physical
stability of emulsion that are flocculation and creaming, coalescence and
breaking, Ostwald ripening, phase inversion and miscellaneous physicochemical
changes. The creaming affect the uniformity of drug distribution but it is
reversible process. Next is coalescence is an irreversible process. The film
surrounding the particle is destroyed and the internal phase tend to coalesce.
The phase-volume ratio that is stable is 50 : 50. Ostwald ripening is where
droplet sizes increase because of large droplets growing at the expense of
smaller ones. Phase inversion is a phenomena that the oil-in-water emulsion
become water-in-oil emulsion. Miscellaneous physicochemical changes are like
the appearance, odour and colour of emulsion.
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
8 test tubes 1
set of 5ml pipette and bulb
1 measuring cylinder 50ml 50ml beaker
2 set of pasture pipette and droppers 15ml centrifuge
Vortex mixing tools Centrifuge machine
Weighing boat
Coulter counter
1 set of mortar and pestle
Viscometer
Light microscope water bath (45°c)
Slides for microscope
refrigerator (4°c)
Materials
Palm oil
Span 20
Arachis oil Tween
80
Olive oil
Sudan III solution (0.5%)
Mineral oil
ISOTON III solution
Distilled water
Procedures
Part
1
1.
8 test tube is labelled and
draws a line about 1cm from bottom of the test tube.
2.
Mix 4ml of oil and 4ml of
distilled water into the test tubes.
Group
|
Oil
|
1, 5
|
Palm Oil
|
2, 6
|
Arachis Oil
|
3, 7
|
Olive Oil
|
4, 8
|
Mineral Oil
|
3.
Then, Span 20 and Tween 80 is
added to the mixture according to the amount given in the Table II . The
mixture is mixed using the Vortex mixing machine for about 45 seconds.The time
needed to reach 1cm line is recorded. 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
|
Time for separation phase (min)
|
||||||||
Stability
|
Table II
4.
After that, drops a few of
Sudan III solution into a few (1g) emulsions that formed in the weighing boat.
Describe and compare color spread in the sample. Take a little sample onto the
microscope slide and observe the sample with using light microscope The
structure and globule size are determined and drawn to compare with other
emulsion.
Part 2
5.
With using wet gum method,
prepare an formulation of Mineral oil Emulsion (50g) by using formula as
followed:
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
|
Emulsion
|
Group
|
Mineral
oil (mL)
|
I
II
III
IV
|
1,5
2,6
3,7
4,8
|
20
25
30
35
|
Table
III
Vanilin ( 2g )
1.
Put 40g emulsion that formed
into 50 ml beaker and homogenization for 2 minutes by using homogenizing
machine.
2.
Take a little (2 g) emulsion
that formed (before and after homogenization) into weighing boat and label.
Drops a few of Sudan III solution and smooth it. Describe and compare the
textures, consistency, degrees of oily appearance and color spread of the sample
by using light microscope.
Homogenizer
Light Microscope
3.
Determine the viscosity of
emulsion (15 g in 50 ml beaker) that formed after homogenization by using
viscometer that calibrated with “Spindle” type LV-4. The sample is exposed at
temperature about 45°C (water bath) for 30 minutes and latter about 4°C
(refrigerator) for 30 minutes. Determine the viscosity of emulsion after
temperature cycle exposure done and emulsion reach room temperature (10-15
minutes).
4.
Put 5 g emulsion that
homogenized into the centrifuge tube and spin it (4500 rpm, 10 minutes, and
25°C). The separation is measured and the ratio is determined and recorded.
Results
Palm Oil
Tub 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
|
0
|
Time taken for phase separation (mins)
|
-
|
-
|
-
|
66
|
76
|
80
|
42
|
1
|
Stability
|
yes
|
yes
|
yes
|
no
|
no
|
no
|
no
|
no
|
*interphase do not reach 1cm after 120 minutes
**To find the average for the time taken, if the
interphase do not reach 1cm after 120 minutes, the time taken is assumed to be
120 minutes.
Arachis Oil
Tub No.
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Span 20 (drops) HLB8.6
|
15
|
12
|
12
|
6
|
6
|
3
|
0
|
0
|
Tween 80 (drops)HLB15
|
3
|
6
|
9
|
9
|
15
|
18
|
15
|
0
|
HLB value
|
9.67
|
10.73
|
11.34
|
12.44
|
13.17
|
14.09
|
15
|
0
|
Time taken for phase separation (mins)
|
-
|
-
|
-
|
-
|
146
|
156
|
161
|
82
|
Stability
|
yes
|
yes
|
yes
|
yes
|
no
|
no
|
no
|
no
|
*interphase do not reach 1cm after 120 minutes
**To find the average for the time taken, if the
interphase do not reach 1cm after 120 minutes, the time taken is assumed to be
120 minutes.
Olive Oil.
Tub 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
|
0
|
Time taken for phase separation (mins)
|
-
|
-
|
-
|
-
|
-
|
32
|
15
|
1
|
Stability
|
yes
|
yes
|
yes
|
yes
|
yes
|
no
|
no
|
no
|
*interphase do not reach 1cm after 120 minutes
**To find the average for the time taken, if the
interphase do not reach 1cm after 120 minutes, the time taken is assumed to be
120 minutes.
Mineral Oil.
Tub 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
|
0
|
Time taken for phase
separation (mins)
|
-
|
-
|
-
|
-
|
-
|
45
|
29
|
4
|
Stability
|
yes
|
yes
|
yes
|
yes
|
yes
|
no
|
no
|
no
|
*interphase do not reach 1cm after 120 minutes
**To find the average for the time taken, if the
interphase do not reach 1cm after 120 minutes, the time taken is assumed to be
120 minutes.
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
At procedure 7
For 25ml olive oil:
Description
|
|
Before homogenization
|
Texture: coarse and not homogenous, cloudy, yellowish
Consistency: not consistent, less viscous
Degree of greasiness: more greasy, more globules
Shape: spherical globules
Size: large globules far from each other and of
different sizes
Colour dispersion: unevenly dispersed, less red
spot
|
After homogenization
|
Texture: smooth and homogenous, milky
Consistency: consistent, more viscous
Degree of greasiness: less greasy
Shape: spherical globules
Size: smaller and uniform size
Colour dispersion: evenly dispersed, more red spot
|
At procedure 8
Viscosity of Emulsion I (20ml palm
oil)
Reading
|
Viscosity (cP)
|
Mean ± SD
|
||
1
|
2
|
3
|
||
Before temperature cycle
|
80
|
90
|
100
|
90.00 ± 10.000
|
After temperature cycle
|
90
|
100
|
100
|
96.67 ± 5.773
|
Difference (%)
|
7.41%
|
|||
Viscosity of Emulsion II (25ml arachis oil)
Reading
|
Viscosity (cP)
|
Mean ± SD
|
||
1
|
2
|
3
|
||
Before temperature cycle
|
389.9
|
419.9
|
419.9
|
409.90 ± 17.321
|
After temperature cycle
|
779.8
|
779.8
|
857.9
|
805.83 ± 45.091
|
Difference (%)
|
96.59%
|
|||
Viscosity of Emulsion III (30ml
olive oil)
Reading
|
Viscosity (cP)
|
Mean ± SD
|
||
1
|
2
|
3
|
||
Before temperature cycle
|
17.5
|
17.0
|
17.5
|
17.33 ± 0.289
|
After temperature cycle
|
5.34
|
5.42
|
5.35
|
5.37 ± 0.044
|
Difference (%)
|
-69.01%
|
|||
Viscosity of Emulsion IV (35ml
mineral oil)
Reading
|
Viscosity (cP)
|
Mean ± SD
|
||
1
|
2
|
3
|
||
Before temperature cycle
|
650
|
500
|
650
|
600.00 ± 86.603
|
After temperature cycle
|
300
|
300
|
300
|
300.00 ± 0.000
|
Difference (%)
|
-50.0%
|
|||
Different in Viscosity of Different Amount of Different Type of Oil
Amount of oil content
(ml)
|
Average viscosity (cP)
( x ± SD)
|
Viscosity difference (%)
|
|
Before temperature cycle
|
After temperature cycle
|
||
20ml palm oil
|
90.00 ± 10.000
|
96.67 ± 5.773
|
7.41
|
25ml arachis oil
|
409.90 ± 17.321
|
805.83 ± 45.091
|
96.59
|
30mi olive oil
|
17.33 ± 0.289
|
5.37 ± 0.044
|
-69.01
|
35ml mineral oil
|
600.00 ± 86.603
|
300.00 ± 0.000
|
-50.0
|
Type of oil
|
Separation Phase
(mm) |
Original emulsion
(mm) |
Ratio
|
Palm Oil
|
30
|
49
|
0.612
|
35
|
48
|
0.729
|
|
Arachis Oil
|
36
|
46
|
0.783
|
20
|
39
|
0.513
|
|
Olive Oil
|
35
|
50
|
0.700
|
37
|
50
|
0.740
|
|
Mineral Oil
|
29
|
50
|
0.580
|
30
|
55
|
0.667
|
Types of oil
|
Height Ratio
|
Mean
(
|
Standard Deviation
(
|
|
Palm Oil
|
0.612
|
0.729
|
0.671
|
0.083
|
Arachis Oil
|
0.783
|
0.513
|
0.648
|
0.191
|
Olive Oil
|
0.700
|
0.740
|
0.720
|
0.028
|
Mineral Oil
|
0.580
|
0.667
|
0.624
|
0.062
|
Formula
of Standard Deviation :
Discussions
1)
What are the HLB values that will
produce a stable emulsion? Discuss.
An emulsion can be considered as stable if it takes longer duration for
the phase separation to occur. But, the in this experiment, we cannot take the duration
for the phase separation for the certain tubes because the duration of phase
separation is too long. So, we consider
the duration that we cannot take is stable because the duration for phase
separation is longer.
Span 20 and tween 80 is the surface active agent that added into the
emulsion to improve the stability of the emulsion. The amount of span20 and
tween80 that needed to add depends on the stability that required for the
emulsion. HLB system gives the guidelines for the selection of emulsifier and
the amount that need to add to achieve the satisfactory stability. The HLB
system assigns a numerical value for each of the emulsifier and known as HLB.
HLB of the emulsifier is the balance of the size and strength of the
hydrophilic (water-loving or polar) and the lipophilic (oil loving or
non-polar) groups of the emulsifier.
An emulsifier that is lipophilic in character is assigned a low HLB
number (below 9.0), and one that is hydrophilic is assigned a high HLB number
(above 11.0). Those in the range of 9-11 are intermediate. Appropriate HLB
value is important in determining the stability of the emulsion. Span is
hydrophobic and it is used to make the w/o emulsion while tween is hydrophilic
and is used to form o/w emulsion. In the stabilization of oil globules, it is
essential that there is a degree of hydrophilicity to confer an enthalpic
stabilizing force and a degree of hydrophobicity to secure adsorption at the
interface. So, a combination of both offers a suitable HLB value which matches
with the system and produces a stable emulsion.
For
palm oil, arachis oil and olive oil,
the HLB value that brings to stable emulsion is 11.34. This means that the
stable emulsion of palm oil can be prepared by adding 12 drops of Span 20 and 9
drops of Tween 80. On the other hands, the HLB value of the mineral oil that can give stable
emulsion is 10.73 which mean 12 drops of Span 20 and 6 drops of Tween 80 are
required for the formation of stable emulsion. These can show that different
types of oils as the dispersed phase required different HLB values of
emulsifier. Thus it requires different combination of emulsifiers in order to
obtain a stable emulsion.
From the experiment for olive oil which is done by our
group which is A7, it was found that the emulsion in test tube 1, 2 ,3 ,4
and 5 with the HLB values as 9.67, 10.73 and 11.34 ,12.44 and 13.17 respectively
which can give the most stable emulsions. The phase separation for the emulsion
in test tube 1, 2, 3, 4 and 5 do not occur after 120 minutes (2 hours) which
means they require longer time for phase separation to occur. Thus we can
conclude that they are the most stable emulsion with the HLB value that ranges
from 9-14. Meanwhile, emulsions from tube 7 and 8 give the lowest stability
where the phase separation time is the shortest. This is because the absence of
surfactant as an emulsifying agent in tube 8 while in tube 7, only Tween 80
present and with a high HLB value that more than 11. HLB value that more than
11 means a hydrophilic emulsifier has been used and it unable to stabilize the
emulsion.
From the experiment for palm oil, it was found that the emulsion from test tube 1, 2 and 3
with the HLB values as 9.67, 10.73 and 11.34 respectively give the most stable
emulsions. The phase separation for the emulsion in test tube 1, 2 and 3 do not
occur even after 120 minutes (2 hours), which means they require longer time
for phase separation to occur. Thus we can conclude that they are the most
stable emulsion with the HLB value that ranges from 9-13. However, the
emulsions from tube 7 and 8 give the lowest stability where the phase
separation time is the shortest. The reason is just the same as the above which
is due to the absence of surfactant as an emulsifying agent in tube 8 while in
tube 7, only Tween 80 present and with a high HLB value that more than 11. HLB
value that more than 11 means a hydrophilic emulsifier has been used and it
unable to stabilize the emulsion.
For the emulsion of arachis oil in the experiment, emulsions from test tube 1, 2 , 3
and 4 with HLB value 9.67 ,10.73, 11.34 and 12.44 respectively have shown the
most stable emulsion. Their interphase do not reach 1cm after 120 minutes (2
hours) which mean that they require a longer duration for the phase separation
to occur. The emulsion in test tube 8 is the least stable emulsion since there
is no emulsifier added into the emulsion to stabilize it. Thus the emulsion
just dispersed less than 3 minutes and separate into 2 phases.
For the emulsion of mineral oil, the most stable emulsion is from the test tube 1, 2 ,3
,4 and 5 with the HLB value 9.67, 10.73
and 11.34 ,12.44 and 13.17. The interphase of emulsion in test tube 1 do not
reach 1cm after 2 hours which means that the emulsion is stable and allow the
even dispersion of the oil globules in the water. As the same with the others
emulsion of different oil, the emulsion from test tube 8 is the least stable
due to the absence of the emulsifier. Phase separation of emulsion in test tube
8 is occurred as soon as the removal of swirling force.
2. Compare the
physical appearance of olive oil emulsion and give comment about it. What is
Sudan III test? Compare the colour distribution in emulsions formed and give
comments about it.
Table III
Emulsion
|
Group
|
Mineral Oil (ml)
|
I
|
1, 5
|
20
|
II
|
2,6
|
25
|
III
|
3,7
|
30
|
IV
|
4,8
|
35
|
In this experiment, four types of mineral
oil (turpentin oil) emulsions are prepared using different contents of mineral
oil. Emulsion I contains 20ml of mineral oil, Emulsion II contains 25 ml of
mineral oil, Emulsion III contains 30ml of mineral oil while Emulsion IV
contains 35ml of mineral oil.
Sudan III test is a test 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. Sudan III has the appearance
of reddish brown crystals. It stained red in oil. . It is not water soluble.
When the emulsion is oil in water, the Sudan III does not disperse in the
emulsion because they will not mix together. While in the water in oil
emulsion, the Sudan III colouring will disperse in the emulsion.
Magnification
(40×10)
|
Physical
appearance
|
Colour
distribution
|
|
Water
droplets dispersed in oil. This is water in oil emulsion. This emulsion is
not dispersing very well due to error.
|
Sudan
III colour dispersed in the emulsion. The emulsion stained light orange.
|
||
Water
droplets dispersed best in oil. This is water in oil emulsion. HLB value of
the emulsion in this test tube is not in the optimum range.
|
Sudan
III colour dispersed in the emulsion. The emulsion stained light orange.
|
||
Test tube 3
|
Water droplets
are not properly dispersed in oil. HLB value of the emulsion in this test
tube is not in the optimum range.
|
Sudan III colour
dispersed in the emulsion. The emulsion stained light orange.
|
|
Test tube 4
|
Water droplets
are not properly dispersed in oil. HLB value of the emulsion in this test
tube is not in the optimum range.
|
Sudan III colour
dispersed in the emulsion. The emulsion stained light orange.
|
|
Test tube 5
|
Water droplets are
not properly dispersed in oil. HLB value of the emulsion in this test tube is
not in the optimum range.
|
Sudan III colour
dispersed in the emulsion. The emulsion stained light orange.
|
|
Test tube 6
|
Water droplets
are not properly dispersed in oil. HLB value of the emulsion in this test
tube is not in the optimum range.
|
Sudan III colour
dispersed in the emulsion. The emulsion stained light orange.
|
|
Test tube 7
|
Water droplets
are not properly dispersed in oil. HLB value of the emulsion in this test
tube is not in the optimum range.
|
Sudan III colour
dispersed in the emulsion. The emulsion stained light orange.
|
|
Test tube 8
|
The emulsion is
totally not formed without surfactant, phase separation occur very fast.
|
Sudan III does
not disperse in the emulsion, globules of Sudan red form on surface of
emulsion.
|
|
3. Plot and discuss:
Amount of
oil content (ml)
|
Average
viscosity (cP)
( x ± SD)
|
Viscosity
difference (%)
|
|
Before
temperature cycle
|
After
temperature cycle
|
||
20ml palm
oil
|
90.00 ±
10.000
|
96.67 ±
5.773
|
7.41
|
25ml
arachis oil
|
409.90 ±
17.321
|
805.83 ±
45.091
|
96.59
|
30mi olive
oil
|
17.33 ±
0.289
|
5.37 ±
0.044
|
-69.01
|
35ml
mineral oil
|
600.00 ±
86.603
|
300.00 ±
0.000
|
-50.0
|
a.
Graph of sample viscosity before and after the temperature cycle vs.
the content of mineral oil.
From
the graph above, viscosity of emulsion with 30mL Mineral Oil content have the
lowest before temperature cycle viscosity while the emulsion with 30mL Mineral
Oil content have the lowest after temperature cycle viscosity.
For
the emulsion with 20mL Mineral Oil content, the before and after temperature
cycle is almost the same, with slightly higher after temperature cycle
viscosity.For 20mL Mineral Oil contained emulsion, it increase in viscosity is
not really that significant as is just increase a little. All we can say is that, after undergoing the
temperature cycle, all of the emulsion experience an increased in
viscosity
The most significant
difference before and after temperature cycle is the emulsion with 25mL Mineral
Oil content where the viscosity increase about 400.25 cP. It is more than twice
the original viscosity. Emulsion with 35mL Mineral Oil content also have a
significant increase in viscosity after the temperature cycle where it
increases about one time of the original.
Theoretically,
viscosity of an emulsion produced increase with increasing amount of mineral
oil in its formulation. From the graph above, the viscosity before temperature
cycle increases as the amount of mineral oil increases until 25mL of mineral
oil is used. This data shows that in this experiment, the viscosity of emulsion
is high with the composition of mineral oil of 20mL and 25mL in emulsions.
However, the viscosity decreases in the emulsion containing 30mL of mineral oil.
Then, the viscosity increases again in emulsion containing 35mL of mineral oil.
For the emulsion after
temperature cycle, the same theory is applied, whereby an increase in amount of
mineral oil will produce a more viscous emulsion. In this experiment, the
viscosity after temperature cycle did increase as the amount of mineral oil
increased until emulsion containing 25mL of mineral oil. After that, the
viscosity decreases in emulsion containing 30mL of mineral oil. The viscosity
of emulsion then increases again in emulsion containing 35mL of mineral oil.
The emulsion that contains 35mL of mineral oil has the highest viscosity while
emulsion that contains 30mL of mineral oil has the lowest viscosity.
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.
a.
Graph of the difference of viscosity (%)
against the different oil contents
The graph above shows the differences
in viscosity against different amount of mineral oil. The higher the difference
in viscosity, the less stable is the emulsion. From the results obtained in
this experiment, emulsion with arachis oil is the most unstable emulsion while
emulsion with mineral oil is the most stable one. This is because the emulsion
type is oil-in-water emulsion. Hence, the dispersed phase of oil droplets will
increase the viscosity. More oil composition in emulsion, more viscosity it
will be. However,from the graph above, an increase in the amount of mineral oil
will increase the difference in viscosity until emulsion containing 25mL of
mineral oil. Emulsion that contains 30 mL of mineral oil decreases dramatically
in viscosity difference. Then, the viscosity difference increases again in
emulsion containing 35 mL of mineral oil.
However, emulsion with palm oil
actually should have the smallest viscosity difference value and is the most
stable one as it contains the least amount of palm oil. This is because when
there is a higher oily phase present in an emulsion, the emulsion is actually
becoming more unstable. Therefore, when these different types of emulsion are
subjected to temperature cycling, the amount of ice crystals formed is usually
directly proportional to the extent of the instability of the emulsion, or the
volume of the oil used. The more the ice crystals are formed, the greater is
the reduction in sample viscosity, and thus the greater is the viscosity
difference (%). Therefore, emulsion with mineral oil is not the most stable
emulsion. These show that errors occur during the experiment.
The inaccurate results might be due
to some errors that occurred during experiment. For example, we use different
volume for the different types of oil. Hence, it causes the existence of two
manipulated variables in one experiment. This causes the result to be
inaccurate and difficult to be compared. The correct way is that we should fix
the type of oil while varying the volume of the mineral oil in order for
experiment result to be valid. Moreover, the exact amount of ingredients used
to prepare the emulsion might not be accurate due to the error while weighing
the ingredients. Besides, inaccurate result might be obtained if the same
spindle is used without washing every time we measure the viscosity of the
emulsion.
4.
Plot graph ratio of phase separation against volume of mineral oil and give
your comment.
Types of oil
|
Height Ratio
|
Mean
(
|
Standard Deviation
(
|
|
Palm Oil
|
0.612
|
0.729
|
0.671
|
0.083
|
Arachis Oil
|
0.783
|
0.513
|
0.648
|
0.191
|
Olive Oil
|
0.700
|
0.740
|
0.720
|
0.028
|
Mineral Oil
|
0.580
|
0.667
|
0.624
|
0.062
|
From the experiment, the
higher the volume of mineral oil, the higher the ratio of phase separation. The
phase separation ratio is not directly proportional to the volume of mineral
oil. Theoretically, the smaller the phase separation ratio, the higher
stability of emulsions. If an emulsion is stable, it is difficult for the oil
and aqueous phase to separate. Hence, when the volume of mineral oil used
increases, the separation phase ratio is also increased. Thus, increasing
amount of oil added will result in higher tendency for the emulsion to be
separated into oil and water. This results in the emulsion produced is more
unstable due to the presence of excess oil.
Sometimes, the problems arise
during preparation of the primary emulsion, this may be caused by phase
inversion, the product which has become a w/o emulsion cannot be diluted with
water. The factors that may cause phase inversion are insufficient shear
between the mortar base and the pestle head, inaccurate measurement of water or
oil, cross contamination of oil and water, use of wet mortar, excessive mixing
of gum and oil, too early or too rapid dilution of the primary emulsion or use
of poor quality acacia.
This may be due to several errors that occur during experiment. For
example, inaccuracy in measuring amount of oil before forming the emulsion,
insufficient homogenisation that has been carried out on emulsion or the height
of separated phase is not measured accurately. Besides, if the volume of each
test tube is not equal during centrifuge, the result of centrifuge will be
inaccurate. Using of wrong method of preparation of emulsion, that is, the wet
gum method may affect the result too. If good emulsion is failed to be
produced, it will affect stability of emulsion which will then affect the
result of the experiment.
5. What is the function of each ingredient
used in the emulsion preparation? How can the different amount of ingredients
influence the physical characteristics and the stability of the emulsion?
Function
|
Note
|
|
Palm oil, Arachis oil, Olive oil and mineral oil
|
The oily phase in the o/w emulsion.
|
Amount
of the mineral oil (oily phase) and the distilled water (aqueous phase) used
is important to determine the type of emulsion formed, whether o/w or w/o
emulsion. The volume of the dispersed phase should not be more than the
volume of the continuous phase. Or else, phase inversion will occur.
|
Acacia
|
It is a natural
product and it can act as an emulsifying agent which can reduces the
interfacial tension and maintains the separation of the droplets in the
dispersed phase. Acacia which acts as the emulsifying agent
|
Since
acacia is a natural product, it can be a good medium for the growth of microorganisms. 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.
|
Syrup
|
Increase the viscosity of the emulsion and acts as sweetening agent
that used to mask the unpleasant taste of the mineral oil in order to
increase the patient compliance.
|
Viscosity of the emulsion will affect on the physical stability and
the rheological characteristic of the emulsion. We have to consider the ease
of pouring out the emulsion from the container. Therefore, the viscosity of
the emulsion has to be strictly monitored to avoid the rheological
problem.
|
Vanillin
|
As flavoring agent which can improve the taste of emulsion thus can
increase patient compliance.
|
Mostly emulsion has a bad taste that most of the patient unable to
accept. Vanillin aids in the taste of emulsion.
|
Alcohol
|
Alcohol is an antimicrobial agent. In this formulation, alcohol acts
as a preservative but the amount of alcohol used should not too high to
prevent toxicity occur.
|
In this formulation, there is a high proportion of water present in
the emulsion which making it more susceptible to microbial contamination. A
suitable antimicrobial agent should be used to prevent instability of
emulsion.
|
Distilled water
|
It is the continuous phase in the emulsion in which the oily
phase is homogenously dispersed with the aid of the surfactants.
|
The distilled water which is the aqueous phase and the oils which is
the oily phase in the emulsion, thus the amount of each phase or the volume
ratio in certain emulsion is determined by the desired type of emulsion,
either o/w or w/o emulsion.
|
Conclusion:
The
combination of different surfactants will results in an accurate HLB value that
is required to form a stable emulsion. Furthermore, different types of emulsifying
agent will results in emulsion with different physical characteristics and
stability. Emulsifying agent adsorb onto the oil and water interface thus
lowering the surface interfacial tension which then in turn will lower the free
energy of the system hence stabilizing the emulsion.
Reference:
1. Aulton, M.E. 1998.
Pharmaceutics: The science of dosage form design. Edinburgh: Churchill
Livingstone.
2. Shariza, Rudy, Ng Shiow
Fern, Thomas. 2011. Pharmacy Practice: Guide to Compounding and Dispensing. Penerbit
UKM: UKM Press
3. Collett, D.M. & Aulton,
M.E. 1990. Pharmaceutical practice. Ed. ke-3. Edinburgh: Churchill Livingstone.
4. 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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