Theories of emulsification:
- Surfactant (Monomolecular adsorption): To reduce the interfacial tension Oil droplets are surrounded by a coherent monolayer of the surfactant which prevents coalescence. If the emulsifier is ionized, the presence of strong charge may lead to repulsion in droplets and hence increasing stability.
- Hydrophillic Colloids (Multimolecular adsorption)
- Finely divided solid particles (solid particles adsorption):They are adsorbed at the interface between two immiscible liquid phases to form Particulate film.
- Monomolecular Adsorption Amphiphiles (surfactants) reduce interfacial tension (to 1 dyne/cm) because of adsorption at interface o/w
- Droplets are surrounded by coherent monolayer that help prevent coalesence (merging) between two droplets
- Surface Charge cause repulsion between globules.
Monomolecular Adsorption (Combination of surfactants) • Combination of surfactants is generally used as it is more effective
- Combination of Sodium cetyl sulphate and cholestrol leads to complex film that produce excellent emulsion
- Hydrophilic Tween can be combined with Lipophilic Span, varying proportions produce desired emulsion… w/o or o/w.
- Multimolecular Adsorption (Hydrocolloids) Hydrophilic colloids (mucilage of gum acacia) are different in action from surfactants
- They do not cause lowering of interfacial tension
- They form multimolecular layer at o/w interface, action of hydrocolloids is because of this reason
- They increase viscosity of dispersion medium
Solid Particles Adsorption • Solid particles that can be wetted by oil as well as water can act as emulsifying agent
- Their concentration is higher at interface
- They form particulate film around dispersed droplets to prevent coalescence
- Example of agents: Bentonite (Al2O3.4SiO2.H2O), Veegum (Magnesium Aluminum Silicate).
Multiple choice questions (MCQs)
1.In the stability of emulsion, which important instability step should be prevented?
2.W/O emulsions is called as
3.The substances which are added to stabilize the emulsions are called
4.Any two immiscible liquids when mixed form an
5.The dispersion of one liquid in another liquid is called as
6.Milk is an emulsion in which
a)Acid particles are dispersed in water
b)Base particles are dispersed in water
c)Water particles are dispersed in liquid fat
d)Liquid fat particles are dispersed in water
7.Why is the emulsion stable with the egg yolk?
a)Due to presence of fat in it
b)Due to presence of lecithin in it
c)Due to presence of albumin in it
d)Due to presence of proteins in it
8.Vanishing cream is an example of
9.What is the process of separating emulsion into its constituents called?
10.Which of the following is an example of an emulsifier?
11.Which of the following is not an example of a water-in-oil emulsion?
a)Cod liver oil
12.What is the difference between vanishing cream and cold cream?
a)Both are examples of oil-in-water emulsions
b)Vanishing cream is an oil-in-water emulsion whereas cold cream is a water-in-oil emulsion
c)Vanishing cream is a water-in-oil emulsion whereas cold cream is anoil-in-water emulsion
d)Both are examples of water-in-oil emulsions
13.Which of the following is not a method to test the type of emulsion?
14.Which of the following statements regarding emulsions is false?
a)Emulsions cannot be separated into their constituent liquids
b)Emulsions show Brownian motion
c)Emulsions show Tyndall effect
d)Emulsions exhibit properties like Electrophoresis and Coagulation
15.Which of the following statement about emulsions is true?
a)Oily drugs cannot be prepared in the form of emulsions
b)Digestion does not involve the process of emulsification
c)Disinfectants like Dettol and Lysol give emulsions of water-in-oil type on mixing with water
d)The cleansing action of soap is based upon the formation of water-in-oil emulsion
- b)Oily emulsion
- c)Emulsifying agent
- d)Liquid fat particles are dispersed in water
- b)Due to presence of lecithin in it
- c)o/w emulsion
- b)Vanishing cream is an oil-in-water emulsion whereas cold cream is a water-in-oil emulsion
- c)Coagulation method
- a)Emulsions cannot be separated into their constituent liquids
- b)Digestion does not involve the process of emulsification
References: 1. GAURAV KUMAR JAIN – THEORY & PRACTICE OF PHYSICAL PHARMACY