1. Industrial Chemistry Part VI
Principles Emulsions
2011

2. Importance of Emulsions
Many foods consist either partly or wholly as food
emulsions, or have been in an emulsified state sometime during their manufacture.
milk, cream, salad cream, mayonnaise, salad dressings, soups, sauces, butter, margarine, beverages, ice cream and coffee whitener.

3. What is Emulsion?
Emulsions are mixtures of two immiscible liquids; in which both the dispersed phase and the dispersion medium are liquids.
Dispersed phase: is the liquid present in a small amount
(small droplets)
The dispersed liquid is known as the internal or discontinuous phase
Continuous phase: is the liquid present in a large amount
(medium)
the continuous phase is known as the external or dispersion medium

4. Classification (Types) of Emulsions
Based on dispersed phase
Oil in Water (O/W): Oil droplets dispersed in water
Water in Oil (W/O): Water droplets dispersed in oil

5. More complex types consist of three or more phases, which can be achieved by e.g. dispersing a w/o-emulsion into a second watery phase, leading to a water-in-oil-in-water-(w/o/w-)emulsion.
In summary
1. oil-in-water (o/w)
2. water-in-oil (w/o)
3. water-in-oil-in-water (w/o/w)
4. oil-in-water-in-oil (o/w/o)
Types Based on Size of Liquid Droplets
µm Macroemulsion
µm Microemulsion

6. Mayonnaise: Oil in Water emulsion
Milk: Oil in Water emulsion
Water in oil emulsion
Sodas: Oil in Water emulsion

7. Emulsion is Thermodynamically Unstable
W/O & O/W ONLY
Most oils are less dense in water, and if oil and water are mixed then the oil will simply float to the surface. In emulsions, the oil is dispersed as liquid droplets through the continuous phase, usually but not necessarily water. Those droplets want to combine together again to form a single drop of oil this means that an emulsion is thermodynamically unstable.
A difference in the densities of the two liquids may cause undesired creaming of the dispersed droplets !!!
What we can do to prevent this unwanted physical process?

8. Stability of emulsions may be engineered to vary from seconds to years depending on application.
How we can do that?
Compositions of Emulsion
Internal/Discontinuous/Dispersed phase (liquid)
External/Continuous phase (Liquid)
Emulsifying agent
Stabilizers

9. Emulsifying Agents
An emulsifier is a molecule with one oil-friendly and one water-friendly end i.e. hydrophilic tail and hydrophobic head. (Do you remember what is that?)
These agents surrounds the oil droplets in water and reduces the tension between the two liquids thus impart stability. Emulsifying agents are often used to help the formation of emulsions

10. Classification of Emulsifiers
Chemical Structure
Mechanism of Action
Synthetic
Natural
Auxiliary agents
dispersed solids
Monomolecular
Multimolecular
Solid Particle Films

11. Synthetic
Anionics: alkali soaps (sodium or potassium oleate)
detergents (sodium lauryl sulfate, sodium dioctyl sulfosuccinate, sodium docusate).
Non-ionics: Sorbitan esters (Spans®), polyoxyethylene derivatives of sorbitan esters (Tweens®), or glyceryl esters
Cationics: benzalkonium chloride, benzethonium chloride
Amphoterics

12. Natural Emulsifying Agents
Natural emulsifying agents are derived from plant and animal tissues and mostly in the form of hydrated lypophilic colloids. These emulsifiers make the protective sheath around the droplets, give droplets a charge so that they repel each other and swell to step-up the viscosity of the liquid.
Although natural agents are inexpensive, safe and non toxic but these are slow in action. So large quantity of emulsifier is required for proper action. Also the natural emulsifiers need preservatives as these are subjected to microbial growth.

13. 1) Carbohydrate Materials:
Acacia, Tragacanth, Agar, Pectin. o/w emulsion.
2) Protein Substances:
-Gelatin, Egg yolk, Caesin o/w emulsion.
3) High Molecular Weight Alcohols:
- Stearyl Alcohol, Cetyl Alcohol, Glyceryl Mono stearate o/w emulsion, cholesterol w/o emulsion.

14. Finely divided solids:
These agents form a particulate layer around dispersed particles. Most will swell in the dispersion medium to increase viscosity and reduce the interaction between dispersed droplets.
Most commonly they support the formation of o/w emulsions, but some may support w/o emulsions.
Examples
Magnesium Hydroxide, Aluminum Hydroxide o/w emulsion
magnesium trisilicate.

15. Mechanism of action of emulsifying agents:
Monomolecular
- Coherent monomolecular film
- flexible film formed by SAA,
- depend on lower the d o/w ,
- can prepare o/w and w/o emulsion
Examples: Synthetic SAA, K laurate

16. Mechanism of action of emulsifying agents:
Multimolecular
Strong rigid film formed, mostly by the hydrocolloid,
- which produce o/w emulsion,
- d is not reduced to any extent ,
- the stability due to strength of the formed interfacial film
Examples: Hydrophilic colloid ( acacia, gelatin)

17. Mechanism of action of emulsifying agents:
Solid particles
Film formed by solid particles that are small in size compared to the droplet of the dispersed phase.
- Particles must be wetted by both phases in order to remain at the interface and form stable film,
- can form o/w and w/o
Examples: Colloid clays(bentonite, Mg(oH)2)

19. Tests Used To Identify Emulsion Type:
Dilution test: based on the solubility of external phase of emulsion.
- o/w emulsion can be diluted with water.
- w/o emulsion can be diluted with oil.

20. Conductivity Test:
water is good conductor of electricity whereas oil is non-conductor. Therefore, continuous phase of water runs electricity more than continuous phase of oil.

21. Dye-Solubility Test:
when an emulsion is mixed with a water soluble
dye such as amaranth and observed under the
microscope.
¡ if the continuous phase appears red, then it
means that the emulsion is o/w type as water is
the external phase
¡ if the scattered globules appear red and
continuous phase colorless, then it is w/o type.

22. Fluorescence test:
Fluorescence test: oils give fluorescence
under UV light, while water doesn’t. Therefore,
O/W emulsion shows spotty pattern while W/O
emulsion fluoresces.

23. Theory of emulsification
Droplets can be stabilized by three methods
By reducing interfacial tension
By preventing the coalescence of droplets.
a. By formation of rigid interfacial film
b. By forming electrical double layer.

24. Theory of emulsification –reduction of interfacial tension
Change from A to B increases surface area of phase A, hence the Due to increased surface energy, the system is thermodynamically unstable.
Phase A
Phase B B A
Change from A to B will increase the surface area of the phase A. If 1 cm3 of minearl oil is dispersed into globules having a diameter of 0.01 micrometer in 1cm3 of water , how much will be the surface area increased?
The surface area will become 600m2 ( greater than a basket ball court); the surface free energy will increase by 8 calories. Soemulsions are thermodynamically unstable and the droplets have tendency to coalesce.
Emulsifying agents are needed to decrease surface tension and to stabilise the droplets.
THEORY OF EMULSIFICATION :
When oil and water are mixed and agitated, droplets of different sizes are produced. However, two immiscible phases tend to have different attractive forces for a molecule at the interface. A molecule of phase A is attracted to phase A but is repelled by Phase B. This produces interfacial tension between two immiscible liquids. (Interfacial tension at a liquid is defined as the work required to create 1 cm2 of new interface.
A fine dispersion of oil and water necessitates a large area of interfacial contact. Its production requires an amount of work equal to the product of interfacial tension and the area change. Thermodynamically speaking , this work is the interfacial free energy imparted to the system. A high interfacial energy favors a reduction of interfacial area, first by making the droplets to get spherical shape( minimum surface area for a given volume) and then by causing them to coalesce (decrease in number of droplets). This is the reason for including the words “Thermodynamically unstable” in definition of opaque emulsions. To make a stable emulsion droplets have to be stabilized so that they do not coalesce.
Droplet Stabilisation : ( Mechanism of action of emulsifying agents)
Droplets can be stabilized by making use of emulsifying agents . Emulsifying agents assist in the formation of emulsion by two mechanisms.
By lowering the interfacial tension And/or
Interfacial tension can be reduced by using surfactants.
By preventing the coalescence of droplets
i. By lowering the interfacial tension (Reduction in interfacial tension – thermodynamic stabilization):
The increased surface energy associated with formation of droplets , and hence surface area in an emulsion can be reduced by lowering of interfacial tension. Assuming the droplets to be spherical
∆ F = 6 γ V/d
∆ F = energy in put required
γ = interfacial tension
V = volume of dispersed phase in ml
d = mean dia of particles
If V= 100 ml of oil , d = 1 μm ( 10-4 cm) , γ o/w = 50 dynes / cm ,
∆ F = 6 x 50 x 100 / (1 x 10-4 ) = 30 x 107 ergs = 30 joules or 30 / = 7.2 cal.
In the above example , addition of emulsifier which reduces γ from 50 to 5 dynes / cm will reduce the surface free energy from 7.2 to 0.7 cal. Such reduction in surface free energy can help to maintain the surface area generated during the dispersion system By ii. preventing the coalescence of droplets Coalescence of droplets can be prevented by two methods - (a) By formation of rigid film ,(b) By formation of electrical double layer.
a. By formation of rigid interfacial film – mechanical barrier to coalescence. Coalescence of droplets can be prevented by formation of films around each droplet of dispersed material. This film forms a barrier that prevents the coalescence of droplets. This film should possess some degree of surface elasticity, so that it does not break when compressed between two droplets. If broken it should form again rapidly. These films are of three types :
i. Monomolecular films :
The surface active agents form a monolayer at the oil water interface. This monolayer serves two purposes :
Reduces the surface free energy.
Forms a barrier between droplets so that they can not coalesce.
Multimolecular films :
Hydrated lyophilic colloids and finely divided solids form multimolecular films around droplets of dispersed oil. They do not reduce the interfacial tension but form a coating around droplets and prevent coalescing. The hydrocolloid which is not absorbed on the surface of droplet, increase the viscosity of continuous phase hence stabilizes the emulsion.
solid particle films
Small solid particles which are wetted to some extent by both oily and aqueous phase, can act as emulsifying agent. If the particles are too hydrophilic, they get dispersed in aqueous phase. If the are too hydrophobic, they get dispersed in oily phase. Other requirement is that the particles should be smaller than the droplet size.
By forming electrical double layer
Presence of a well developed charge on the droplet surface increases stability by causing repulsion between approaching drops. This charge is likely to be greater if ionized emulsifying agent is employed. i/v fat emulsions are stabilized with lecithin due to the electrical repulsion.
In an o/w emulsion stabilized by sodium soap, the hydrocarbon tail is dissolved in the oily phase and ionic heads are facing the continuous aqueous phase. As a result the surface of the droplet is studded with –vely charged carboxylic group. This produces a surface charge on the droplet.. The cations of opposite charge are oriented near the surface , producing a double layer of charge. The potential produced by double layer creates a repulsive effect between the oil droplets and thus hinder coalescence.
Emulsifying agents are needed to decrease the interfacial tension and to stabilize the emulsion.

25. Oriented-Wedge Theory:
- mono molecular layers of emulsifying agents are curved around a droplet of the internal phase of the emulsion.
Multimolecular films

26. Theory of emulsification -Formation of electrical double layer+ - -
Emulsion made with sodium soap. - + + + - - + -
Oil -
Water - + + +
By forming electrical double layer
Presence of a well developed charge on the droplet surface increases stability by causing repulsion between approaching drops. This charge is likely to be greater if ionized emulsifying agent is employed. i/v fat emulsions are stabilized with lecithin due to the electrical repulsion.
In an o/w emulsion stabilized by sodium soap, the hydrocarbon tail is dissolved in the oily phase and ionic heads are facing the continuous aqueous phase. As a result the surface of the droplet is studded with –vely charged carboxylic group. This produces a surface charge on the droplet.. The cations of opposite charge are oriented near the surface , producing a double layer of charge. The potential produced by double layer creates a repulsive effect between the oil droplets and thus hinder coalescence. - - + - -
Electrical double layer at oil-water interface

27. Interfacial films
Solid particle film: These agents form a particulate layer around dispersed particles. Most will swell in the dispersion medium to increase viscosity and reduce the interaction between dispersed droplets.
Most commonly they support the formation of o/w emulsions, but some may support w/o emulsions.

28. Methods of emulsion preparation:
On small scale:
¡ Porcelain mortar and pestle
¡ On large scale:
Mechanical stirrer

29. Methods of emulsion preparation:
Emulsifier is triturated with the oil in perfectly
dry porcelain mortar
water is added at once
triturate immediately, rapidly and continuously
(until get a clicking sound and thick white cream is formed, this is primary emulsion)
the remaining quantity of water is slowly added to form the final emulsion

30. English or Wet Gum Method
triturate gum with water in a mortar to form a mucilage
oil is added slowly in portions the mixture is triturated
after adding all of the oil, thoroughly mixed for several minute to form the primary emulsion
Once the primary emulsion has been formed remaining quantity of water is added to make the final emulsion.

31. Bottle or Forbes Bottle Method
It is extemporaneous preparation for volatile oils or oil with low viscosity.
gum + oil (dry bottle)
Shake
water (volume equal to oil) is added in portions with vigorous shaking to form primary emulsion
remaining quantity of water is added to make the final emulsion

32. Auxiliary Emulsifying Agents
A variety of fatty acids (e.g., stearic acid), fatty alcohols (e.g., stearyl or cetyl alcohol), and fatty esters
(e.g., glyceryl monostearate) serve to stabilize emulsions through their ability to thicken the emulsion. Because these agents have only weak emulsifying properties, they are always use in combination with other emulsifiers

33. Be stable .
Be compatible with other ingredients .
Be non – toxic .
Bossess little odor , taste , or color .
Not interfere with the stability of efficacy of the
active agent .

35. Emulsion Stability:
The instability of pharmaceutical emulsions may be classified as the following:
Flocculation and creaming
b) coalescence and breaking
c) Phase inversion
d) Miscellaneous physical and chemical change

37. Emulsion Stability

38. Flocculation and creaming:
¡ Flocculation - The small spheres of oil join
together to form clumps or flocs which rise or
settle in the emulsion more rapidly than
individual particles.
¡ Creaming - it is a concentration of the floccules
of the internal phase formed upward or
downward layer according to the density of
internal phase.