emulsion-1

Question 1

definition

Answer 1

 An emulsion is a thermodynamically unstable system consisting of at least two immiscible liquid
phases one of which is dispersed as globules in the other liquid phase stabilized by a third substance
called emulsifying agent.
 An emulsion is an intimate mixture of two immiscible liquids that exhibits an acceptable shelf life near
room temperature.
 In emulsion, the component which is present in the form of small droplet is called internal /
discontinuous/dispersed phase and the other component present as liquid is called external phase or
continuous phase or dispersion medium.
 Most emulsion will have droplets with diameters of 0.1 to 100μm.

Question 2

internal/external phase

Answer 2

 The dispersed liquid is known as the Internal or Discontinuous phase. The droplet phase is called the
dispersed phase or internal phase whereas the dispersion medium is known as the External or
Continuous phase.
 The liquid in which droplets are dispersed is called the external or continuous phase.

Question 3

coposition of emulsion

Answer 3

1-aqeous phase
2-oily phase
3-emulsifying agents

Question 4

aqeous phase

Answer 4

 Consists of purified or the ionized water which contains water soluble drug preservatives, coloring and
flavouring agents.
 If tap water or hard water is used in the formulation it has adverse effect on the stability of emulsions,
particularly those emulsion containing fatty acids and soap as emulsifying agents.

Question 5

oily phasw

Answer 5

 The oily phase of an emulsion consists of fixed, volatile or mineral oil which contains oil soluble
vitamins and antiseptics.
 The oil used in the formation of an emulsion should be auto-oxidation as well as from microbes.

Question 6

emulsifying agents

Answer 6

 It is the component of emulsion which bound the two immiscible liquids by forming a film around the
dispersed globules and makes the emulsion stable.
 So, it prevents the two liquids (water and oil) from separating as two distinct layers.
 The emulsifying agents are of great importance in any type of emulsion i.e. o/w, w/o, multiple or micro
emulsion.
 This process is called emulsification.

Question 7

advantages of emulsion

Answer 7

 A dose of an unpalatable drug may be administered in a palatable liquid Form (e.g. Cod liver oil, fish
oil emulsion).
 An oil-soluble drug can be dissolved in the disperse phase and be successfully administered to a
patient in a palatable form. (e.g. Propofol, diazepam)
 The aqueous phase can be easily flavoured.
 The texture/consistency of the product is improved as the ‘oily’ sensation in the mouth is successfully
masked by the emulsification process.
 Absorption may be enhanced by the diminished size of the internal phase.
 Emulsions offer potential in the design of systems capable of giving controlled rates of drug release
and affording protection to drugs susceptible to oxidation or hydrolysis.
 Emulsions have been used to deliver poorly water-soluble drugs, such as general anesthetics and anti-
cancer compounds, via the intravenous route

Question 8

diadvantages

Answer 8

 Preparation needs to be shaken well before use
 Measuring device needed for administration
 Need a degree of technical accuracy to measure a dose
 Storage conditions may affect stability
 Bulky, difficult to transport and prone to container breakages
 Liable to microbial contamination which can lead to cracking

Question 9

classification of emulsion

Answer 9

1. BASED ON DISPERSED PHASE:
    Oil in Water (O/W): Oil droplets dispersed in water
    Water in Oil (W/O): Water droplets dispersed in oil
2. BASED ON DIAMETER OF LIQUID DROPLETS:
    Droplets may be 5,000 Å (0.5μm) in diameter
   Muhammad Muneeb
    Macro emulsions (thermo- Dynamically unstable)
    diameter of droplets is 100Å (0.01μm) - 1000 Å (0.1μm)
    Micro emulsions (thermo- Dynamically stable)

Question 10

mutiple dispertions

Answer 10

 Multiple emulsions are complex poly-dispersed systems where both oil in water and water in oil
emulsion exists simultaneously which are stabilized by hydrophilic and lipophilic surfactants
respectively. In these types of emulsions three phases are present:
 In (water in oil in water) w/o/w emulsion an oil droplet enclosing a water droplet are suspended in
water.
 In (oil in water in oil) o/w/o emulsion a water droplet enclosing an oil droplet are suspended in oil.
 In these “emulsions within emulsions,” any drug present in the innermost phase must now cross two
phase boundaries to reach the external, continuous phase.
 Whether the aqueous or the oil phase becomes the dispersed phase depends primarily on the
emulsifying agent used and the relative amounts of the two liquid phases.
 Most pharmaceutical emulsions designed for oral administration are of the O/W type; emulsified
lotions and creams are either O/W or W/O, depending on their use.

Question 11

general types of pharmaceutical emulsion

Answer 11

 Lotions
 Vitamin oils
 Creams
 Ointments

Question 12

theories of emulsions

Answer 12

 Several theories have been proposed to explain how emulsifying agents act in producing the multi-
phase dispersion and in maintaining the stability of the resulting emulsion.

o Theory of viscosity
o Fischer theory
o Surface-tension theory
o Oriented-wedge theory
o Plastic or Interfacial film theory
 The most prevalent theories are the surface-tension theory, the oriented-wedge theory, and the
interfacial film theory.

Question 13

surface tension theory

Answer 13

 According to the surface tension theory of emulsification, the use of surfactants results in a reduction
in the interfacial tension of the two immiscible liquids reducing the repellent force between the liquids
diminishing each liquid’s attraction for its own molecules.
 Thus, surfactants enable large globules to break into smaller globules, and prevent small globules from
coalescing into larger globules.

Question 14

plastic or interfacial film theory

Answer 14

 When two immiscible liquids come in contact, the force causing each liquid to resist breakage into
smaller particles is known as interfacial tension. When a high interfacial tension existed between two
liquids emulsification is difficult, and if the tension could be reduced emulsification facilitated.
 The interfacial film theory proposes that the emulsifier forms an interface between the oil and water,
surrounding the droplets of the internal phase as a thin layer of film adsorbed on the surface of the
drops.
 The film prevents the contact and coalescing of the dispersed phase; the tougher and more pliable the
film, the greater the stability of the emulsion
 Greater is the interfacial tension, less stable will be the emulsion as more attraction of the dispersed
globules experiences

Question 15

harkin-oreinted wedge threory

Answer 15

 The oriented wedge theory proposes that the surfactant forms monomolecular layers around the
droplets of the internal phase of the emulsion. The theory is based on the assumption that emulsifying
agents orient themselves about and within a liquid relative to their solubility in that particular liquid.
 Because surfactants have a hydrophilic or water loving portion and a hydrophobic or water hating
portion (but usually lipophilic or oil-loving), the molecules position or orient themselves into each
phase
 Depending on the shape and size of the molecules, their solubility characteristics, and, thus, their
orientation, the wedge shape theory proposes that emulsifiers surround either oil globules or water
globules.
 An emulsifying agent, having a greater hydrophilic character than hydrophobic character, will
promote oil in water emulsions.
 Conversely, water in oil emulsions result with the use of an emulsifier that is more hydrophobic than
hydrophilic.
 In this theory the surfactant emulsifier molecules are assumed be shaped like wedges; therefore, it is
termed “Oriented wedge” theory.

Question 16

theory of viscocity

Answer 16

 It states that more viscous emulsion the greater is the stability. But it is not always true.
 This theory is holds good for emulsions prepared with gums as emulsifying agents
 Example:
o Milk has low viscosity but most stable, O/W emulsion.
o Cold Cream is an example of more viscous emulsion, O/W emulsion

Question 17

fischers theory

Answer 17

 Fischer’s observed that the use of specific ratios of emulsifying agent to continuous phase, he claimed
that the quantity of water in these specified ratios was all used up in forming a colloidal hydrate.
 It states that disperse phase form colloidal hydrate or colloidal complex.
 Example:
o O/W emulsion, oil form colloidal complex and in W/O emulsion water form colloidal complex
and known as solvate

Question 18

additive for formulation of emulsion

Answer 18

 Antioxidants
 Antimicrobial Preservative
 Auxiliary Emulsifiers
 Emulsifying Agents

Question 19

anti-oxidants

Answer 19

 Autoxidation occurs by free radical reaction
 Can be prevented by
o Absence of oxygen
o A free radical chain breaker
o By reducing agent
 Examples:
o Gallic acid, Propyl gallate - pharmaceuticals and cosmetics - Bitter taste
o Ascorbic acid – Suitable for oral use products
o Sulphites - Suitable for oral use products
o L-tocopherol - pharmaceuticals and cosmetics -Suitable for oral preparations
o e.g. those containing vitamin A
 The oxidative decomposition of certain excipients, the oil phase, and some pharmaceuticals is
possible in emulsions, not only due to the usual amount of air dissolved in the liquid and the possible
incorporation of air during the preparation of the product, but also the large interfacial area between
the oil and water phase.
 The selection of the appropriate antioxidant depends on such factors as:
o Stability
o Compatibility with the ingredients of the emulsion
o Toxicity
o Effectiveness in emulsions
o Odor
o Taste
o Distribution between the two phases

Question 20

anti-microbrial preervative

Answer 20

The preservative must be:
 Less toxic
 Stable to heat and storage
 Chemically compatible
 Reasonable cost
 Acceptable taste, odor and color.
 Effective against fungus, yeast, bacteria.
 Available in oil and aqueous phase at effective level concentration.
 Preservative should be in unionized state to penetrate the bacterial membrane
 Preservative must no bind to other components of the emulsion, because the complexes are ineffective
as preservatives. Only the concentration of free, or unbound, preservative is effective
Examples:
 Acids and acid derivatives – Benzoic acid, Antifungal agent

 Aldehydes – Formaldehyde - Broad spectrum
 Phenolics – Phenol (Broad spectrum)
 Quaternaries – Chlorhexidine and salts (Broad spectrum)
 Benzalkonium chloride
 Cetyl trimethyl ammonium bromide
 Mercurials – Phenyl mercuric acetate (Broad spectrum)

Question 21

viscocity agents

Answer 21

 Viscosity agents are added in emulsion.
o Hydrophilic colloids (naturally occurring gums)
o Partially synthetic polymers, such as cellulose derivatives (e.g., Methylcellulose,
hydroxypropylmethylcellulose, sodium carboxymethylcellulose)
o Synthetic polymers (carbomer polymer).
 These materials are hydrophilic in nature and dissolve or disperse in water to give viscous solutions
and function as emulsion stabilizers.
 High molecular weight alcohols (stearyl alcohol, cetyl alcohol, and glyceryl monostearate) are
employed primarily as thickening agents and stabilizers for o/w emulsions of certain lotions and
ointments used externally.
 Cholesterol and cholesterol derivatives may also be employed in externally used emulsions and to
promote w/o emulsions

Question 22

emulsifying agents

Answer 22

 They are the substances added to an emulsion to prevent the coalescence of the globules of the
dispersed phase. They are also known as emulgents or emulsifiers.
 They help in formation of emulsion by three mechanisms.
o Reduction in interfacial tension – thermodynamic stabilization
o Formation of a rigid interfacial film – mechanical barrier to coalescence, it should possess
some degree of surface elasticity and should not thin out and rupture when sandwiched between
two droplets
o Formation of an electrical double layer – electrical barrier to approach of particles.

Question 23

ideal properties

Answer 23

Ideal properties of emulsifiers:
o Be stable
o Be compatible with other ingredients
o Be non – toxic
o Possess little odor , taste , or color
o Not interfere with the stability and efficacy of the active agent
o Promote emulsification to maintain the stability of the emulsion for the intended shelf life of
the product

Question 24

desirable proporties of emulsifying agents

Answer 24

o Some of the desirable properties of an emulsifying agent are that it should be surface active
and reduce surface tension to below 10 dynes/cm.
o Be adsorbed quickly around the dispersed drops as a condensed, non-adherent film that will
prevent coalescence.
o Impart to the droplets an adequate electrical potential so that mutual repulsion occurs
o Increase the viscosity of the emulsion.
o Be effective in a reasonably low concentration

Question 25

HLB system

Answer 25

 HLB (Hydrophilic lipophilic balance) is the balance of strength of hydrophilic or lipophilic portion of
surfactant molecule.
 Hydrophilic lipophilic balance (HLB) of a surfactant is a measure of the degree to which it is
hydrophilic or lipophilic, determined by calculating values for the different regions of the molecule.
 Each emulsifying agent has a hydrophilic portion and a lipophilic portion, with one or the other being
more or less predominant and influencing the type of emulsion.
 As the emulsifier becomes more hydrophilic, its solubility in water increases and the formation of an
O/W emulsion is favored. Conversely, W/O emulsions are favored with the more lipophilic
emulsifiers.

 Griffin developed a scale based on the balance between these two opposing tendencies. This so-called
HLB scale is a numerical scale. The more hydrophilic surfactants have high HLB numbers (in excess
of 10), whereas surfactants with HLB numbers from 1 to 10 are considered to be lipophilic.
 HLB system usual range is between 1 and 20.

Question 26

RELATIONSHIP BETWEEN HLB RANGE AND SURFACTANT APPLICATION:

Answer 26

HLB Range Use
0-3 Antifoaming agent
4-6 W/O emulsifying agent
7-9 Wetting agent
8-18 O/W emulsifying agent
13-15 Detergents
10-18 Solubilizing agent

Question 27

classification of emulsifers

Answer 27

 Emulsifying agents may be classified in accordance with the type of film they form at the interface
between the two phases
 The main purpose of this film—which can be a monolayer, a multilayer, or a collection of small
particles adsorbed at the interface—is to form a barrier that prevents the coalescence of droplets that
come into contact with one another.
 The ionic nature of a surfactant is an important consideration when selecting a surfactant for an
emulsion.
 Nonionic surfactants are effective over pH range 3–10; cationic surfactants are effective over pH range
3–7; and, anionic surfactants require a pH of greater than 8.

Question 28

synthetic emulsifying agents (monomolecular films)

Answer 28

 Those surface-active agents that are capable of stabilizing an emulsion do so by forming a monolayer
of adsorbed molecules or ions at the oil–water interface
 Reduce interfacial tension and make the emulsion thermodynamically more stable. This results in a
more stable emulsion because of a proportional reduction in the surface free energy.
 Droplets are surrounded now by a coherent monolayer that prevents coalescence between approaching
droplets.
 If the emulsifier forming the monolayer is ionized, the presence of strongly charged and mutually
repelling droplets increases the stability of the system.
 With un-ionized, nonionic surface active agents, the particles may still carry a charge; this arises from
adsorption of a specific ion or ions from solution
 The majority of emulsifiers forming monomolecular films are synthetic, organic materials.
 The majority of emulsifiers forming monomolecular films are synthetic, organic materials.
 May be subdivided into anionic, cationic, and nonionic, depending on the charge possessed by the
surfactant.

Question 29

anionics

Answer 29

o Anionics: In the anionic subgroup, the surfactant ion bears a negative charge.
 Example: The potassium, sodium, and ammonium salts of lauric acid (Potassium
laurate) and oleic acid are soluble in water and are good O/W emulsifying agents.

Question 30

cationic

Answer 30

o Cationics: The surfactant ion bears a positively charged. These compounds have marked
bactericidal properties. This makes them desirable in emulsified anti-infective products such
as skin lotions and creams. The pH of an emulsion prepared with a cationic emulsifier lies in
the pH 4 to 6 ranges.
 Example: Quaternary ammonium compounds (Cetyltrimethyll ammonium bromide)
Cationic emulsifiers should not be used in the same formulation with anionic
emulsifiers because they will interact.

Question 31

non-ionic

Answer 31

o Non-ionics: Have no charge, find widespread use as emulsifying agents when they possess
the proper balance of hydrophilic and lipophilic groups within the molecule.
 Example: Glyceryl esters, polyoxyethylene glycol esters and ethers, and the sorbitan
fatty acid esters and their polyoxyethylene derivatives.

Question 32

natual emulsifying agents

Answer 32

 Emulsifying agents derived from natural (i.e., Plant and animal) sources
 Also known as Hydrocolloid Emulsifying agents
 These materials form hydrophilic colloids, when added to water, and produce o/w emulsions. Although
their surface activity is low, these materials achieve their emulsifying power by increasing the viscosity
of the aqueous phase.
 Hydrated lyophilic colloids form a protective sheath (Multi-molecular films) around the droplets
 Most of the emulsifiers that form multimolecular films are obtained from natural sources and are
organic
 They differ, however, from the synthetic surface-active agents in that:
o They do not cause an appreciable lowering of interfacial tension and
o They form a multi- rather than a monomolecular film at the interface
 Their action as emulsifying agents is due mainly to the multi-molecular film because the films thus
formed are strong and resist coalescence.
 These act as a coating around the droplets and render them highly resistant to coalescence, even in the
absence of a well-developed surface potential.
 Furthermore, any hydrocolloid not adsorbed at the interface increases the viscosity of the dispersion
medium; this enhances emulsion stability.
 Because the emulsifying agents that form multilayer films around the droplets are invariably
hydrophilic, they tend to promote the formation of o/w emulsions.
 Examples:
o Plant origin: Polysaccharides (Acacia, tragacanth, agar, pectin, lecithin)
o Animal origin: Gelatin, Lecithin (Egg yolk), Cholesterol (Wool fat)

Question 33

finely dispersed solids

Answer 33

 Solid particle films also known as Particulate films
 Form a particulate “film” around dispersed particles.
 These particles rely on adsorption to interfaces and like the hydrophilic colloids, function by forming
a physical barrier to coalescence.
 Finely divided small solid particles that are wetted to some degree by both oil and water act as
emulsifying agents. If the particles are too hydrophilic, they remain in the aqueous phase; if too
hydrophobic, they are dispersed completely in the oil phase. This results from their being concentrated
at interface, where they produce a particulate film around the dispersed droplets to prevent coalescence.
 E.g.
o Colloidal clays:
 Bentonite, (Al2O3.4SiO2.H2O)
 Veegum (Magnesium Aluminium silicate) it is employed most extensively as stabilizer
in cosmetic lotions and creams.
 Magnesium trisilicate
o Metallic hydroxides:
 Magnesium hydroxide

Question 34

auxiliary emulsifers

Answer 34

 Auxiliary (Secondary) emulsifying agents include those compounds that are normally incapable
themselves of forming stable emulsion. Their main value lies in their ability to function as thickening
agents and thereby help stabilize the emulsion.

 Auxiliary emulsifying agents that are amphiphilic in nature are, in some cases, capable of forming gel
or liquid crystalline phases with the primary emulsifying agent when combined with water and oil.
 This type of behavior may help to stabilize emulsions due to an increased viscosity, as observed in
topical creams.
 Alternatively, gel or liquid crystalline phases may prevent coalescence by reducing van der Waals
forces between particles or by providing a physical barrier between approaching particles of the
internal phase.

Question 35

preparation of emulsion

Answer 35

 For small scale work emulsions can be prepared by the following methods:
o Dry gum method
o Wet gum method
o Bottle method

Question 36

dry gum method

Answer 36

 This method is called as continental method
 This method is also known as 4 : 2: 1 method because these figures represent the proportions of oil,
water and gum acacia required for the preparation of primary emulsion.
 That is, for example, if there are 40 ml of fixed oil to be emulsified then 10 example, if there are 40ml
of fixed oil to be emulsified then 10 gm of gum acacia and 20 ml of water or vehicle will be required
for preparing the primary emulsion.
 Measure the given quantity of oil with a clean and dry measure and transfer it to a dry mortar. To this
add the calculated quantity of acacia and triturate rapidly so as to form a uniform mixture.
 Then add the required quantity of water for primary emulsion and triturate rapidly without ceasing till
a clicking sound is produced and the product becomes white or nearly white.
 At this stage the emulsion is known as primary emulsion. Then add more of water to produce the
required volume.
 If any soluble ingredient is also to be incorporated, that must be dissolved in the second portion of
water to be added after making the primary emulsion and to produce the final volume.

Question 37

wet gum method

Answer 37

 This method is also called English method.
 The proportions of oil, water and gum are some as for dry gum method. In this method the calculated
quantity of gum is triturated with water to form mucilage.
 Then the given amount of oil is incorporated in small portions with rapid titration until a clicking sound
is produced and the product becomes white or nearly so.
 When the primary emulsion is formed, the titration in continued for few minutes more and then more
of water is incorporated in successive small portions to produce the required volume.

Question 38

bottle method

Answer 38

 Bottle method is used for the preparation of emulsions of volatile and other non-viscous oils.
 The emulsions can be prepared by both the dry gum and wet gum methods.
 Because of low viscosity the volatile oils require greater amount of gum for emulsification therefore
the proportions for oil, water and gum for primary emulsion are 4 : 4 : 2.
 In this method the oil is put in a large bottle and then the powdered dry gum is added. The bottle is
shaken vigorously until the oil and gum are mixed thoroughly.
 Then the calculated amount of water is added all at once and the mixture is shaken vigorously until
primary emulsion is formed.
 More of water is added in small portions with constant agitation after each addition, to produce the
final volume.

Question 39

physical stability of emulsions

Answer 39

 A stable emulsion may be defined as a system in which the globules retain their initial character and
remain uniformly distributed throughout the continuous phase.
 The stability of pharmaceutical emulsion is characterized by the:
o Absence coalescence of the internal phase
o Absence of creaming
o Maintenance of elegance with respect to appearance, order colour and other physical properties
 The instability of pharmaceutical emulsions may be classified follows:
o Flocculation and creaming
o Coalescence and breaking
o Some physical and chemical changes and
o Phase inversion

Question 40

flocculation and creaming

Answer 40

 Creaming is a phenomenon characterized by the accumulation of droplets of the dispersed phase on
the top of the emulsion.

Question 41

coalescence and breaking or crackig

Answer 41

 Cracking involves coalescence of the dispersed globules and provides eventual separation of the
emulsion in to two phases. Some of the factors that cause cracking are:
o The addition of a substance that is incompatible with the emulsifier may destroy its emulsifier
ability.
o An increase in temperature may coagulate certain types of emulsifying agents (proteins)
o Freezing of aqueous phase will produce ice crystals that may exert unusual pressure on the oil
globules.
o Attempts to incorporate excessive amount of dispersed phase may cause cracking of an
emulsion.

 Those factors which reduce the chances of coalescence & breaking include:
o Uniformity of particle size of the dispersed phase.
o Increase in viscosity of the emulsion to optimum level since this hinders flocculation
coalescence.
o Phase volume ratio: the dispersed phase should be less than 74% otherwise the oil globules
may coalescence and emulsion may break.

Question 42

physical and chemical changes

Answer 42

 Natural gums, starches etc. used as emulsifiers may contain excessive amount of bacterial load.
Bacterial growth may cause change in PH and consequent breakdown of emulsion.
 Synthetic emulsifiers are comparatively more stable.
 Some emulsifiers such as soaps carry electric changes. Neutralization of the charge by on added
substance may cause breakdown of the emulsion. Natural gums, starches etc. used as emulsifiers may contain excessive amount of bacterial load.
Bacterial growth may cause change in PH and consequent breakdown of emulsion.
 Synthetic emulsifiers are comparatively more stable.
 Some emulsifiers such as soaps carry electric changes. Neutralization of the charge by on added
substance may cause breakdown of the emulsion.

Question 43

phase inversion

Answer 43

 In phase inversion the o/w type emulsion changes into w/o type and vice versa.
 It may be brought about by the addition of an electrolyte or by changing the phase volume ratio or by
temperature change.

Question 44

pharmaceutical applications of emulsions

Answer 44

 Emulsions can be used to administer orally unpleasant tasting drugs such as liquid paraffin, cod liver
oil, and castor oil in a palatable formulation.
 Oil soluble as well as water soluble materials can be formulated in to a single dosage form as an
emulsion. For example, oil soluble vitamins, A, D, E, and water soluble ones like B & C can be
formulated as a palatable fine emulsion. Such formulation also leads to better absorption of vitamins.
 Radio-opaque emulsions are used for diagnostic applications such as X-ray examination.
 O/w type emulsions are used for i/v administration of oil and fats with high caloritic value patients
who are to ingest food orally.
 Emulsions of both o/w &w/o types have extensively been used to prepare pharmaceutical preparation
for external used and cosmetic preparation such as cream and lotion.
 Emulsification has also been used aerosol products to prepare foams.
 Drugs sensitive to oxidation or hydrolysis can be stabilized by formulating them in form of emulsion.
 Bioavailability of certain poorly soluble drugs can be improved by dissolving them in oil and
emulsifying agents