When two immiscible liquids, such as oil and water, are in contact, interfacial tension causes each liquid to maintain as small a surface as possible. If two immiscible liquids are shaken together, the liquids break up into small droplets, greatly increasing the total surface area of each liquid. The increased energy associated with the increased area is supplied by the mechanical energy of agitation. The work of emulsion formation may be expressed as the interfacial tension time the change in interfacial area. As the interfacial tension is a measure of the force to be overcome in mixing two immiscible liquids and substance which lowers interfacial tension will facilitate the preparation of an emulsion. For an emulsion to be stable, the droplets of the internal phase must be prevented from coming together to form a larger globule and eventually a layer. Thus, the substance used to help form the emulsion must also help to prevent the droplets from coming together either by forming a rigid film arround each droplet of by imparting a charge to the droplets which will cause them to repel each other. Cationic and anionic surfactants like sodium lauryl sulfate form the later while nonionic surfactants (Tween 80)and polymeric film formers (Acacia, Methylcellulose) do the former. In this laboratory we will use both types of surfactants and film formers.
Surfactants migrate to the interface between the two phases and reduce interfacial tension and form a film which prevent the coalescence of the globules of the internal phase. These globules, however, are still capable of movement within the external phase. If the internal phase has a lower density that the external phase the globules will rise. This is called creaming. Even though creaming has occured if the film that has been formed is rigid the globules will not coalesce. An emulsion that has creamed without coalescence will easily redistribute with shaking.
PROCEDURE:
The gum Acacia is often used as a film former when making extemporaneous emulsions. The method of manufacture requires that you first make a thick emulsion of fixed proportion and then add any additional aquoeus ingredients that are needed. There are two ways to manufacture that primary emulsion. First you must determine the total volume of oil in the preparation. This represents 4 parts of the primary emulsion. You will have to measure out a volume of water equal to two parts and a weight of acacia equal to one part. The dry gum or Continental method requires that you place the acacia in a dry mortar and add the oil. Mix for a very brief time. Now add the water all at once and mix until the primary emulsion is formed. The wet gum or English method requires that you make a mucilage with the acacia and water. You will add the acacia to the water a little at a time being sure it is completely hydrated. Now you add the oil a little at a time with constant mixing until the primary emulsion is made.
. Part A - Prepare 100 ml of a 50% mineral oil in water emulsion using both methods.
Divide each product in half and use the hand homogenizer on one portion of each product.
Take a sample of each of the four products and mix one or two drops of amaranth solution with it. Take a drop of the colored mixture and look at it under the microscope. Draw a picture of what you see in all four cases and describe your observations about the nature of all four products.
Tragacanth is sometimes used in place of acacia. Prepare 50 ml of an emuslion with the same ratio of oil and water but replace the acacia with one tenth the quantity of tragacanth as acacia. Repeat the experiment with the hand homogenizer and the amaranth. Compare the results.
. Part B - Prepare an emulsion by mixing 30 ml of olive oil with 30 ml of lime water in a 3 or 4 oz bottle. Divide the emulsion into three parts. Test one part using the drop dilution method to determine the type of emulsion that was formed. Add 1 ml of dilute hydrochloric acid to the second portion and record the changes if any. To the third portion add one ml of oleic acid. Mix well and observe the changes.
Prepare another emulsion with 30 ml of cottonseed oil and 30 ml of Milk of Magnesia in a 3 or 4 oz bottle. Determine the type of emulsion that was formed.
Prepare a fourth emulsion according to the following formula.
Calamine
3 g
Zinc Oxide
3 g
Olive Oil
24 ml
Bentonite Magma 24 ml
in lime water
Record your method of manufacture. Determine the type of emulsion formed.
. Part C - Semi solid emulsions are often called creams. Two popular creams are vanishing cream called that because it seems to vanish as you rub it into the skin and brushless shave cream. Both of these formulas have the three key components of any emulsion. A water phase, an oil phase and an emusifier Prepare 30 g of each.
Formula I - Vanishing Cream
Stearic Acid
25 g
Triethanolamine
2 g
Glycerin
12 g
Water
61 g
Using a water bath, melt the stearic acid. Dissolve the glycerin and triethanolamine in the water and heat to 700 . With gentle stirring so that air is not incorporated, add the aqueous phase to the melted stearic acid.
Formula II Brushless Shave Cream
Stearic Acid
12.5 g
Span 60
2.5 g
Tween 60
1 g
White Petrolatum
110. g
Propylene Glycol
5 g
Water
67 ml
28 % Ammonium hydroxide 2 ml
Lavender oil
0.1ml
Melt the stearic acid, span , tween, and petrolatum and bring to 800 . Heat the propylene glycol and water to 800 . Add the ammonium hydroxide to the aqueous phase and quickly add the oily phase with moderate mixing. Stir until the temperature drops to 550 . Add lavender oil and mix.
Compare the two products. Which components are in each of the three catagories - the water phase, the oils phase, and the film formers.