It has already been noted that on purely thermodynamic grounds, emulsions are physically unstable. A reduction of the interfacial area by coalescence reduces the system’s energy, and this process is thermodynamically favoured. However, thermodynamic stability of emulsions differs from pharmaceutical stability as defined by the formulator or the consumer. Acceptable stability in a pharmaceutical dosage form does not require thermodynamic stability. If an emulsion creams up (rises) or creams down (sediments), it may still be pharmaceutically acceptable as long as it can be reconstituted by a modest amount of shaking. Similar considerations apply to cosmetic emulsions; however, in the latter, creaming is usually unacceptable because any unsightly separation makes the product cosmetically inelegant. It is important, therefore, to remember that the standard of stability depends to a large extent on the observer, since subjective observations or opinions by themselves do not suffice to define such a parameter as acceptable stability.

Physical stability-

• Flocculation
• Creaming
• Coalescence and breaking
• Ostwald ripening
• Phase inversion

Flocculation: Flocculation is described as reversible aggregation of droplets of the internal phase in the form of three-dimensional clusters. In flocculated emulsion, the globules do not coalesce and can be easily redispersed upon shaking. The reversibility of this type of aggregation depends on the strength of the interaction between particles as determined by the chemical nature of the emulsifier, the phase volume ratio and the concentration of dissolved substances, especially electrolytes and ionic emulsifiers. In the absence of a mechanical barrier at the interface (weak interfacial films due to insufficient amounts of emulsifier), emulsion droplets aggregate and coalesce rapidly. In other words, flocculation differs from coalescence primarily by the fact that the interfacial film and the individual droplets remain intact. Flocculation and emulsion rheology are closely related. The viscosity of an emulsion depends to a large extent on flocculation, which restricts the movement of particles and can produce a fairly rigid network. Agitation of an emulsion breaks the particle–particle interactions with a resulting drop of viscosity, i.e. shear thinning.

Creaming: Under the influence of gravity, the dispersed droplets or floccules tend to rise (upward creaming) or sediment (downward creaming), depending on the differences in specific gravities betweenthe phases, to form a layer of more concentrated emulsion, the cream. Generally, a creamed emulsion can be restored to its original state by gentle shaking. The process of creaming, which inevitably occurs if there is a density difference between the phases, should not be confused with flocculation, which is due to particle interactions resulting from the balance of attractive and repulsive forces. Most oils are less dense than water so that the oil droplets in o/w emulsions rise to the surface to form an upper layer of cream. In w/o emulsions, the cream results from sedimentation of water droplets and forms the lower layer. The Stokes’ equation is very useful in understanding the process of creaming:

Rate of creaming = d²(Ƿ_s-Ƿ_o)g/18ƞ

where d is the diameter of the particles of dispersed phase (cm), Ƿs the density of the dispersion medium (g/cm3), Ƿo the density of the dispersed phase (g/cm3), g the acceleration due to gravity (cm/s2) and ƞ the viscosity of the dispersion medium (poise).

Coalescence and breaking: Coalescence is a growth process during which the emulsified particles join to form larger particles. It is an irreversible phenomenon that occurs due to the rupture of the interfacial film surrounding the dispersed globules. Coalescence is not the only mechanism by which dispersed phase droplets increase in size. If the emulsion is polydispersed and there is significant miscibility between the oil and water phases, then

Ostwald ripening, where droplet sizes increase due to large droplets growing at the expense of smaller ones, may also occur. This destabilizing process occurs when small emulsion droplets (less than 1 μm) have higher solubilities than do larger droplets (i.e. the bulk material) and consequently are thermodynamically unstable. Any evidence for the formation of larger droplets by merger of smaller droplets suggests that the emulsion will eventually separate completely or break. The major factor that prevents coalescence in emulsions is the mechanical strength of the interfacial barrier. Thus, good shelf life and absence of coalescence can be achieved by the formation of a thick interfacial film. Hence, various natural gums and proteins are useful as auxiliary emulsifiers when used at low levels, but can even be used as primary emulsifiers at higher concentrations.

Phase inversion: An o/w emulsion prepared with a monovalent water-soluble soap (sodium stearate) can be inversed to the w/o type by adding calcium chloride due to the formation of divalent soap(calcium stearate). Inversion may also be produced by alterations in the phase-volume ratio. For example, if an o/w emulsifier is mixed with oil and a little quantity of water, a w/o emulsion is produced by agitation. Since the water volume is less, it forms a w/o emulsion. But when more water is added slowly, phase inversion occurs and an o/w emulsion is produced. Inversion has also been observed when an emulsion, which has been prepared by heating and mixing the two phases, is cooled. It is due to the temperature-dependent changes in solubility of the emulsifying agents. Phase inversion can be prevented by choosing proper emulsifying agents in suitable concentrations. Wherever possible, it is better to ensure that the internal phase does not exceed 74% of the total volume of the emulsion.

Multiple choice questions (MCQs)

1.What is the emulsifier present in milk that makes it stable?

a)Maltose

b)Lactose

c)Lactic acid bacillus

d)Casein

2.o/w microemulsion containing hydrophilic surfactants produces

a)Translucent emulsion

b)Transparent emulsion

c)Milky white emulsion

d)Untense white emulsion

3.Events that are likely to occur sequentially, in physical unstability are

a)Flocculation, creaming, breaking and coalasence

b)Flocculation, creaming, coalescence and breaking

c)Breaking, coalescence, flocculation and creaming

d)Coalascence, flocculation, creaming and breaking

4.Upward creaming means ____ rate of sedimentation

a)Negative

b)Positive

c)Same

d)No change

5.Emulsifier used to stabilize the w/o emulsion

a)SLS

b)Span 20

c)Tween 20

d)Tragacanth

6.An emulsifier is considered to be ideal, if it is soluble in

a)Aqueous phase

b)Oil phase

c)Both a and b

d)None of the above

7.Emulsion made with tweens are

a)w/o

b)o/w

c)clear

d)unstable

8.Emulsion containing more than two phases are called as

a)Mixed emulsion

b)Multiple emulsion

c)Complex emulsion

d)None of the above

9.Emulsion is a

a)Stable preparation

b)Thermodynamically unstable preparation

c)Biphasic system

d)Both b and c

10.The coalescence rate of o/w emulsion is _____ than w/o emulsion

a)Lower

b)Greater

c)Same

d)None of the above

11.Auxillary emulsifying agents are used to stabilize the emulsion. They act on the principle

a)Adjusting the HLB value

b)Strengthening the non polar tails of the emulsifier

c)Strengthening the polar tails of the emulsifier

d)Thickening the continuous phase

12.Downward creaming means ____ rate of sedimentation

a)Negative

b)Positive

c)Same

d)No change

13.A mixture of span 20 and tween 20 forms ­­­____ type of emulsion

a)w/o

b)o/w

c)milky

d)hard

14.Which of the following is/are theories of emulsification?

a)Monomolecular adsorption theory

b)Multimolecular adsorption theory

c)Solid particle adsorption theory

d)All of the above

15.Which of the following is not the cause of instability in an emulsion?

a)Upward creaming

b)Phase inversion

c)Downward creaming

d)Mottling

Solution:

1. d)Casein
2. b)Transparent emulsion
3. b)Flocculation, creaming, coalescence and breaking
4. b)Positive
5. b)Span 20
6. c)Both a and b
7. b)o/w
8. b)Multiple emulsion
9. d)Both b and c
10. b)Greater
11. d)Thickening the continuous phase
12. a) Negative
13. a)w/o
14. d)All of the above
15. d)Mottling

References:

1. GAURAV KUMAR JAIN – THEORY & PRACTICE OF PHYSICAL PHARMACY, 1st editio 2012 Elsevier, page no. 240-244.

2. Martins Physical Pharmacy, 6th edition 2011, page no. 768-771.

For More Standard and Quality Question Bank you can Join Our Test Series Programme for GPAT, NIPER JEE, Pharmacist Recruitment Exam, Drug Inspector Recruitment Exams, PhD Entrance Exam for Pharmacy

List of Successful GPATINDIAN CANDIDATES

Participate in Online FREE  GPAT  TEST: CLICK HERE

 Participate in Online FREE  Pharmacist  TEST: CLICK HERE 

Participate in Online FREE  Drug Inspector  TEST: CLICK HERE 

Participate in CSIR NET JRF Mock Test

Participate GATE Mock Test

The post Emulsions: Physical stability and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam appeared first on Gpatindia: Pharmacy Jobs, Admissions, Scholarships, Conference,Grants, Exam Alerts.

• 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?

a)Breaking

b)Coalescence

c)Flocculation

d)Creaming

2.W/O emulsions is called as

a)Aqueous emulsion

b)Oily emulsion

c)Alcoholic emulsion

d)Electrophoresis

3.The substances which are added to stabilize the emulsions are called

a)Dialyser

b)Aggregates

c)Emulsifying agent

d)Peptizing agent

4.Any two immiscible liquids when mixed form an

a)Aerosol

b)Emulsion

c)Gel

d)Sol

5.The dispersion of one liquid in another liquid is called as

a)Solid sol

b)Sol

c)Emulsion

d)Gel

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

a)Aerosol

b)Gel

c)o/w emulsion

d)w/o emulsion

9.What is the process of separating emulsion into its constituents called?

a)Emulsifying agent

b)Centrifugation

c)Demulsification

d)Emulsification

10.Which of the following is an example of an emulsifier?

a)NaCl

b)CaCO₃

c)C₁₅H₃₁COONa

d)CH₃COOH

11.Which of the following is not an example of a water-in-oil emulsion?

a)Cod liver oil

b)Butter

c)Cold cream

d)Milk

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?

a)Microscopic method

b)Conductance method

c)Coagulation method

d)Dye method

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

Solution:

1. b)Coalescence
2. b)Oily emulsion
3. c)Emulsifying agent
4. b)Emulsion
5. c)Emulsion
6. d)Liquid fat particles are dispersed in water
7. b)Due to presence of lecithin in it
8. c)o/w emulsion
9. c)De-emulsification
10. c)C₁₅H₃₁COONa
11. d)Milk
12. b)Vanishing cream is an oil-in-water emulsion whereas cold cream is a water-in-oil emulsion
13. c)Coagulation method
14. a)Emulsions cannot be separated into their constituent liquids
15. b)Digestion does not involve the process of emulsification

References: 1. GAURAV KUMAR JAIN – THEORY & PRACTICE OF PHYSICAL PHARMACY

For More Standard and Quality Question Bank you can Join Our Test Series Programme for GPAT, NIPER JEE, Pharmacist Recruitment Exam, Drug Inspector Recruitment Exams, PhD Entrance Exam for Pharmacy

List of Successful GPATINDIAN CANDIDATES

Participate in Online FREE  GPAT  TEST: CLICK HERE

 Participate in Online FREE  Pharmacist  TEST: CLICK HERE 

Participate in Online FREE  Drug Inspector  TEST: CLICK HERE 

Participate in CSIR NET JRF Mock Test

Participate GATE Mock Test

The post Emulsions: Theories of Emulsification and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam appeared first on Gpatindia: Pharmacy Jobs, Admissions, Scholarships, Conference,Grants, Exam Alerts.

Some common emulsions are milk (where the dispersion of fat molecules or droplets in the aqueous solution) and also butter (which is the dispersion of droplets of particles of an aqueous solution in the fat).

Types of Emulsion:

Emulsions can be classified on the basis of the properties of the dispersed phase and the dispersion medium.

• Oil in water (O/W): In this type of emulsion, the oil will be the dispersed phase and water will be the dispersion medium. The best example for o/w emulsion is milk. In milk, the fat globules (which act as the dispersed phase) are suspended in water (which acts as the dispersion medium).
• Water in oil (w/o): In this type, water will be the dispersed phase and oil will be the dispersion medium. Margarine (a spread used for flavouring, baking and working) is an example of water in oil emulsion.

Microemulsions- In spite of their similarity, the terms microemulsion and emulsion characterize two very different systems both by their physical and thermodynamic properties and by their structure. In both cases, the systems consist of an aqueous phase, a lipophilic phase and a surfactant agent. A co-surfactant is also required for microemulsions. Microemulsions actually exist when the percentage of oil or water in the internal phase is low (<10%). These dispersions of oil or water nanodroplets in an external phase are stabilized by an interfacial film of surfactant and co-surfactant. The addition of co-surfactant results in a homogeneously dispersed system, which can diffuse the light, appear clear and homogeneous to the naked eye and, as opposed to emulsions, is thermodynamically stable. The co-surfactants have three functions: (1) they provide very low interfacial tensions required for the formation of microemulsions and their thermodynamic stability, (2) they can modify the curvature of the interface based on the relative importance of their apolar groups and (3) they act on the fluidity of the interfacial film.

The main characteristic of microemulsions is their transparent appearance due to the high level of dispersion of the internal phase, the size of which ranges from 100 to 1000 Å.

The microemulsions are Newtonian liquid and are not very viscous. These dispersed systems are isotropic and in terms of the manufacture, their formation is spontaneous, do not require much energy and are thermodynamically stable.

O/w micellar solution- Blending of a small amount of oil with water results in a two-phase system because ‘water and oil do not mix’. If the same small amount of oil is added to an aqueous solution of a suitable surfactant in the micellar state, the oil may preferentially dissolve in the interior of the micelle because of its hydrophobic character. This type of micellar microemulsion is called an o/w micellar solution.

W/o micellar solution- In these systems, sometimes called reverse micellar solutions, water molecules are found in the polar central portion of a surfactant micelle, the nonpolar portion of which is in contact with the continuous lipid phase.

A microemulsion in which a water-insoluble oil or drug is ‘dissolved’ in an aqueous surfactant system plays an important role in drug administration.

Table 1 – Methods for the determination of type of emulsion

Multiple choice question (MCQs)

1.Dye test which is used to identify type of emulsion is that which dye is used?

a)Scarlet red

b)Scarlet green

c)Crystal violet

d)Methylene blue

2.In conductivity test, if bulb glows on passing electric current so what would be the type of emulsion?

a)w/o emulsion

b)o/w emulsion

c)micro emulsion

d)multiple emulsion

3.In micro emulsion, the size of globule are

a)1µm

b)0.1 µm

c)0.01 µm

d)10 µm

4.Multiple emulsion can be designed as

a)o/w

b)w/o/w

c)o/w/o

d)both b and c

5.Which emulsion is mainly used for taste masking purpose?

a)Multiple emulsion

b)w/o

c)micro emulsion

d)o/w

6.Dilute emulsion follows

a)Non Newtonian flow

b)Newtonian flow

c)Thixotrophy

d)Rheopexy

7.If viscosity of continous phase increase so creaming

a)No change

b)Increase

c)Decrease

d)None of the above

8.In case of coalescence

a)Dispersed droplet does not fuse

b)Globule size decrease

c)No. of globules increase

d)Dispersed droplets tend to fuse

9.If the density of two phase is more so

a)Stability of emulsion is less

b)Stability of emulsion is more

c)Does not affect the stability

d)None of the above

10.In case of o/w emulsion, creaming takes place at

a)Down side

b)Up side

c)At interface between two phase

d)None of the above

11.Ideal phase volume ratio per stable emulsion

a)25:75

b)50:50

c)75:25

d)33:67

12.Thermodynamically emulsion is

a)Stable

b)Unstable

c)Both

d)None

13.Creaming is

a)Reversible

b)Irreversible

c)Both

d)Difficult to predict

14.Upward creaming is observed in

a)w/o

b)o/w

c)both

d)micro

15.HLB value of w/o emulsifying agent is

a)2-3

b)3-6

c)7-9

d)8-16

Solutions:

1. a)Scarlet red
2. b)o/w emulsion
3. c)0.01 µm
4. d)both b and c
5. a)Multiple emulsion
6. b)Newtonian flow
7. c)Decrease
8. d) Dispersed droplets tend to fuse
9. a)Stability of emulsion is less
10. b)Up side
11. a)25:75
12. b)Unstable
13. a)Reversible
14. b)o/w
15. d)8-16

References:

1. GAURAV KUMAR JAIN – THEORY & PRACTICE OF PHYSICAL PHARMACY, 1st edition 2012 Elsevier, page no. 237-240.

2. Martins Physical Pharmacy, 6th edition 2011, page no. 763.

For More Standard and Quality Question Bank you can Join Our Test Series Programme for GPAT, NIPER JEE, Pharmacist Recruitment Exam, Drug Inspector Recruitment Exams, PhD Entrance Exam for Pharmacy

List of Successful GPATINDIAN CANDIDATES

Participate in Online FREE  GPAT  TEST: CLICK HERE

 Participate in Online FREE  Pharmacist  TEST: CLICK HERE 

Participate in Online FREE  Drug Inspector  TEST: CLICK HERE 

Participate in CSIR NET JRF Mock Test

Participate GATE Mock Test

The post Emulsions: Types and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam appeared first on Gpatindia: Pharmacy Jobs, Admissions, Scholarships, Conference,Grants, Exam Alerts.