Assessment on the Impact of Different Ingredients on the Characteristics of an Emulsion Formulations
Date
12nd May 2015
Objectives
- To determine the effect of HLB surfactant on the stability of emulsion.
- To investigate the physical effect and stability on an emulsion formulation due to the usage of different types of emulsifying agents.
Introduction
An emulsion is a mixture of two or more liquids that are normally immiscible. Emulsion should be used when both the dispersed and continuous phase are liquids. Oil-in-water emulsion is when oil is the dispersed phase and water is the continuous phase meanwhile water-in-oil emulsion is when the water is the dispersed phase and the oil is the continuous phase. Emulsion stability refers to the ability of an emulsion to resist change in its properties. There are four types of instability in emulsion namely flocculation, creaming, coalescence as well as Ostwald ripening. The emulsion is stabilized by adding emulsifying agents. There are three types of emulsifying agents namely hydrophilic colloids, surfactants and finely divided particles. Hydrophilic-lipophilic balance(HLB) technique is used to prepare a stable emulsion. This technique will help to determine the most accurate amount of surfactant needed to prepare a stable emulsion.
Apparatus
8 test tubes 1 set 5 ml pipette and bulb
150 ml measuring cylinder 1 50 ml beaker
2 Sets of Pasture pipette and droppers 1 15 ml Homogenizer tube
Vortex mixer Homogenizer
Weighing boat Viscometer
1 set of mortar & pestle Water bath (45 oC)
1 set of mortar & pestle Water bath (45 oC)
Light microscope Refrigerator (4 oC)
Microscopic slide
Materials
Palm oil Span 20
Mineral oil Tween 80
Arachis oil Sudan III solution (0.5%)
Olive oil
Distilled water
Procedures
- Test tube is labelled and make one line 1 cm from the end of test tube.
- 4 ml of Palm Oil is mixed with 4 ml of distilled water into the test tube.GroupOil1,5Palm Oil2,6Arachis Oil3,7Olive Oil4,8Mineral Oil
- Span 20 and Tween 80 are dropped into the mixture of oil and distilled water (refer table II). Test tube is closed and mixed with the Vortex Mixer device for 45 second. Time required to achieve phase separation line 1 cm is recorded. The HLB value for each sample is recorded. Table II Test tube no12345678Span 20 (drop)15121266300Tween 80 (drop)36991518150
- A few drops of Sudan III is dropped into 1 g of emulsion in the weighing boat and spreading evenly. Dispersion of color in the sample being compared and discussed. The sample is spread on the microscope slide and is observed under the light microscope. The shape and size of globule formed were drew, discussed and compared.
- Mineral Oil emulsion 50 g was formed using the wet gum method according to the following formula.Mineral oilRefer table IIIAcacia6.25gSyrup5 mlVanillin2gAlcohol3 mlDistilled water, qs50 mlEmulsionGroupMineral Oil (ml)I1,2,320II4,5,625III7,830
- 2g of emulsion is taken before and after homogenization into the weighing boat and labelled. Sudan III solution is dropped into the emulsion and was mix evenly. The texture, consistency, degree of oil and physical shape and dispersion of color of sample under light microscope were discussed and compared.
- Viscosity of emulsion is measured (15g in 50ml beaker) that formed after homogenization process by using viscometer which was calibrated using “spindle” LV-4. The sample was exposed to 45°C (water bath) about 30 minute and was cool at 4°C (freezer) about 30 minute. The viscosity is measured after exposure in temperature cycle and emulsion reached room temperature (10-15minute).
- 5g emulsion that was homogenize is inserted into the centrifudge and centrifugation (4500rpm, 10 minute, 25°C). The height separation is measured and height ratio is determined.
Reading
|
Viscosity (cP)
|
Average + SD
| ||
1
|
2
|
3
| ||
Before temperature cycle
|
210
|
204
|
186
|
200 + 10.2
|
After temperature cycle
|
222
|
174
|
182
|
192.67 + 21.0
|
Difference(%)
|
-3.8
| |||
Height (mm)
| |
Phase separation
|
35
|
Initial emulsion
|
50
|
Height ratio
|
0.70
|
Characteristic
|
Before homogenization process
|
After homogenization process
|
Texture
|
Uneven size distribution of globules
|
Even size distribution of globules
|
Consistency
|
Low
|
Moderate
|
Degree of oil appearance
|
Oily surface
|
Less oily surface
|
Colour Dispersion
|
Colour of continuous phase is brighter than disperse phase
|
Colour of continuous phase is darker than disperse phase
|
Discussions
HLB value increases from test tube 1 to test tube 7. HLB value is actually used to determine or to measure the degree to which the surfactant is hydrophilic or lipophilic. Span 20 and tween 80 is a surfactant that used in this experiment. Test tube that contains both surfactants has regular shape of globule. While for test tube 8, there is absence of surfactant present in the test tube, therefore the shape of globule is irregular.
Question 1
What are the values of HLB used to make a stable emulsion? Discuss.
Stable emulsion is an emulsion that does not undergo phase separation. In this experiment, emulsion is prepared in eight different test tubes with different amount of Span 20 and Tween 80 drops. There are four different types of oils being used namely Palm Oil, Arachis Oil, Olive Oil and Mineral Oil. The suitable HLB values to make a stable emulsion can be determined by using the HLB value formula. The formula is as below :
HLB value is actually used to determine or to measure the degree to which the surfactant is hydrophilic or lipophilic. HLB value of 0-3 is used for anti-foaming agents, HLB value of 3-6 is used for water-in-oil emulsifying agents, HLB value of 7-9 is used for wetting as well as spreading agents, HLB value of 8-18 is used for oil-in-water emulsifying agents and HLB value of 15-20 is used for solubilisers. This HLB value guideline can be used to determine the most accurate value of HLB to use in order to produce a stable emulsion.
Question 2
Compare the physical characteristic of Mineral Oil emulsion formed and give review for it. What is Sudan Test III? Compare the colour diffusion among the emulsion formed and give review.
Sample
|
Observation
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
- Beautiful bubbles with regular shapes are taken before homogenization meanwhile bubbles with irregular shapes are taken after homogenization.
- The magnification scale for bigger bubbles is 10X.
- The magnification scale for small bubbles is 4X.
Sudan III is a lysochrome which is a fat-soluble diazo dye. It is used to colour nonpolar substances like oils, fats, waxes and various hydrocarbon products. It has an appearance of reddish brown crystals. In this experiment, Sudan III test is used to differentiate oil-in-water emulsion and water-in-oil emulsion. Theoretically, if Sudan III is added to an emulsion and the dispersed phase appears red, it should be oil-in-water emulsion.
Before homogenization the red stain appears uneven meanwhile after homogenization the red stain appears more even. Even staining makes the globules look more evenly distributed.
Question 3
Plot and comment it.
i. Graph of sample viscosity before and after the temperature cycling vs the different content of mineral oil.
Emulsion
|
Content of mineral oil (ml)
|
Average Viscosity (cP)
(Average ± SD)
|
Difference Viscosity (%)
(Average ± SD)
| |
Before the temperature cycle
|
After the temperature cycle
| |||
I
|
20
|
409.23 ± 17.32
|
805.83 ±45.09
|
96.91%
|
II
|
25
|
486.57 ± 40.41
|
973.14 ±45.09
|
100.0%
|
III
|
30
|
161.67 ±49.14
|
413.33 ± 90.18
|
155.66%
|
IV
|
35
|
200 ± 10.20
|
192.67 ± 21.0
|
-3.67%
|
The viscosity is the measure of internal friction in a liquid or the resistance to a flow. In the experiment, we use four different contents of mineral oil which are 20ml, 25ml, 30ml and 35ml of mineral oil. In the experiment, each emulsion is heated at 45°C for 30 minutes then the emulsion is put into refrigerator for freezing at 4°C for 30 minutes. This step is carried out to compare the physical instabilities of the emulsion under the normal stored condition. When the emulsion is heated and frozen, the small ice crystals will be formed continually and the adsorbed layer of the emulsifying agent at the oil-water interface will be disrupted. By doing so, the weakness in the structure of the film will become more apparent quickly.
Theoretically, as the volume of mineral oil added is increased, the viscosity of emulsion will be increased. The viscosity of emulsion before heating is higher than after heating. It is because of the formation of ice crystals leads to the decrease in the viscosity of the emulsion. Therefore, the viscosity of the emulsion before temperature cycling is higher than that of after temperature cycling. Besides, the drop in the viscosity of the emulsion after temperature cycling may be due to the occurrence of phase inversion. This means that the initially o/w emulsion is now converted into w/o emulsion.
From the graph, it can be seen that the graph obtained is not followed the pattern in theory explained above. This is due to some errors occurred during conducting the experiments such as we did not wait until room temperature then directly measure the viscosity of emulsion. As the temperature of emulsion is too low after take out from refrigerator, this causes the increase in the viscosity of emulsion. The viscosity of the emulsion measured is not increasing according to the increasing volume of mineral oil because there is some leakage of the emulsion when transferring the emulsion from beaker to the viscometer.
ii. Graph of difference viscosity against different amount of mineral oil added.
Graph above shows that difference in viscosity against different amount of oil. From the graph, it is shown that there will be an increase in the difference of viscosity after temperature cycle except emulsion that contains 35mL of mineral oil. In theory, the greater the amount of mineral oil, the greater the viscosity difference. The higher the concentration of dispersed phase, the higher the viscosity difference. This means that the amount of globules increases, as the increases of the viscosity difference. The viscosity difference will indicate a weaker and less stable emulsion. Thus, the higher the volume of dispersed phase, the stability of the emulsion decreases and phase inversion may occur. According to the graph, emulsion that contains 35mL of mineral oil is decreased with viscosity difference. The result is different from what is expected due to some experimental errors might have occur such as during the preparation of emulsion, the amount of materials used was not in the exact proportion. Another error is occurred during using the viscometer such as continue using the machine without washing every time finish measuring the viscosity that will lead to the inaccuracy of the data.
Question 4
Plot a graph on the ratio of the phase separation due to the centrifugation process against different mineral oil content. Give comments.
Based on the graph on the ratio of the phase separation due to the centrifugation process against different mineral oil content above, the ratio of the phase separation decrease in the increase of the amount of mineral oil being used in the formulation. Based on the theory, the ratio of phase separation should increase in the increasing of the amount of mineral oil in the formulation because the amount of oil exceeding the amount which give the stability to the mixture. The phase separation for those having high amount of mineral oil will be faster than the lower one due to unstable emulsion formed. however, the results obtained from the experiment does not follow the theory. This problem may due to some errors while carrying out the experiment. The error may include the mistakes in measuring the amount mineral oil and other substances to be used. Although, the height of the separation may not being measured accurately due to slanting position of the separation which affect from the position of tubes in centrifugation machine. Thus, every groups might measure the phase separation at different sites.
Question 5
What is the function for each material used in the formation of emulsion? How the used of different materials can affect the physical characteristics and the stability of emulsion?
Acacia, span 20 and tween 80 is an emulsifying agent. Emulsifying agent is used to prevent coalescence of the globules of the dispersed phase. Emulsifying agent will concentrate and adsorbed onto the oil/water interphase to provide a protective barrier around the dispersed droplets. Emulsifier will stabilize the emulsion by reducing the interfacial tension of system. Some agents, will enhanced stability by imparting a charge on the droplet surface thus reducing the physical contact between the droplets and decreasing the potiental for coalescence.
Syrup is used as liquid vehicle. Also act as sweetening agent of emulsion and increase viscosity of emulsion. Vanillin used as flavouring agent. Alcohol is natural preservative that can prevent microbiological contamination of the emulsion.
The HLB value of the surfactant will affect the stability of the emulsion. An emulsifier that has a low HLB will tend to be oil-soluble emulsion, while a high HLB will tend to be water-soluble emulsion. Besides, the stability of the emulsion also depend on the amount of oil. The higher the amount of oil, the greater the viscosity difference in which the emulsion give an unstable emulsion.
References
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2902331/
No comments:
Post a Comment