Theories of emulsification and stabilization (DLVO Theory, monomolecular adsorption, multimolecular adsorption, Film formation, and solid particle adsorption). Physical instabilities of emulsions (creaming, coalescence and breaking, and phase inversion).

Theories of Emulsification and Stabilization

Emulsions are thermodynamically unstable systems, so they require emulsifying agents to reduce interfacial tension and provide stability. Several theories explain how emulsifiers stabilize emulsions:

1. DLVO Theory

DLVO theory explains stability in terms of the balance between attractive (van der Waals) and repulsive (electrostatic) forces between dispersed droplets.

• If repulsion dominates, = the Emulsion remains stable

• If attraction dominates, = Droplets aggregate and destabilize
  This theory is widely used to understand the stability of colloidal and emulsion systems in pharmaceutical systems.

2. Monomolecular Adsorption Theory

According to this theory, emulsifying agents (like surfactants) form a single molecular layer at the oil–water interface.

• Hydrophilic head faces aqueous phase

• Lipophilic tail faces oil phase
  This monolayer reduces interfacial tension and prevents droplet coalescence.

3. Multimolecular Adsorption Theory

Here, emulsifiers (such as hydrophilic colloids like gelatin or acacia) form a multilayered film around dispersed droplets.

• A thick adsorption layer increases steric stabilization

• Prevents droplets from coming close enough to merge

4. Film Formation Theory

This theory suggests that emulsifying agents form a continuous, coherent film at the interface.

• Film acts as a mechanical barrier

• Prevents droplet fusion and coalescence

• Can be rigid (solid-like) or flexible, depending on emulsifier type

5. Solid Particle Adsorption (Pickering Emulsions)

Finely divided solid particles (e.g., clays, silica) adsorb at the oil–water interface.

• Particles form a rigid protective layer around droplets

• Strongly prevent coalescence

• Used in pharmaceutical and cosmetic formulations

Physical Instabilities of Emulsions

Emulsions undergo several physical changes during storage, which affect their quality and performance:

1. Creaming

• Upward movement of dispersed droplets due to the density difference

• Reversible on shaking

• Does not involve a droplet size change

2. Coalescence

• Fusion of droplets into larger droplets

• Leads to permanent instability

• Eventually causes phase separation

3. Breaking (Cracking)

• Complete separation of oil and water phases

• Irreversible process

• Emulsion cannot be restored easily

4. Phase Inversion

• Dispersed phase and continuous phase interchange

• Example: oil-in-water (O/W) becomes water-in-oil (W/O)

• Can be induced by a change in emulsifier concentration, temperature, or phase volume ratio

1. According to DLVO theory, stability of an emulsion is mainly due to:

A. Increase in viscosity
B. Balance between attractive and repulsive forces
C. Reduction in interfacial tension only
D. Sedimentation equilibrium

Answer: B Balance between attractive and repulsive forces

According to the DLVO Theory, the stability of an emulsion is mainly due to the balance between van der Waals attractive forces and electrostatic repulsive forces between dispersed droplets.

VTotal = VAttractive + VRepulsive

Explanation:

• Attractive forces tend to bring droplets together, causing flocculation/coalescence.

• Repulsive forces prevent droplets from coming close enough to aggregate.

• A stable emulsion exists when repulsive forces are sufficiently high to overcome attractive forces.

Why are other options incorrect?

• A. Increase in viscosity → Helps reduce creaming but is not the basis of DLVO theory.

• C. Reduction in interfacial tension only → Important for emulsification, not the main DLVO stabilization mechanism.

• D. Sedimentation equilibrium → Related to suspensions, not DLVO stabilization of emulsions.

2. In DLVO theory, the repulsive force between dispersed droplets arises mainly because of:

A. Van der Waals attraction
B. Brownian movement
C. Electrical double layer
D. Density difference

Answer: C

Correct Answer: C. Electrical double layer

According to the DLVO theory (Derjaguin–Landau–Verwey–Overbeek theory), the stability of emulsions and colloidal dispersions depends on the balance between:

• Attractive Van der Waals forces

• Repulsive electrostatic forces

The repulsive force arises mainly due to the formation of an electrical double layer around dispersed droplets or particles. When droplets acquire the same surface charge, they repel each other, preventing aggregation and coalescence.

This electrostatic repulsion increases the stability of the emulsion or colloidal system.

Why Other Options Are Incorrect

A. Van der Waals attraction.

Van der Waals forces are attractive forces, not repulsive.
They tend to pull droplets or particles together, promoting:

• Flocculation

• Aggregation

• Coalescence

In DLVO theory, these forces oppose stability.

B. Brownian movement

Brownian movement refers to the random motion of particles due to collisions with solvent molecules.

It helps keep small particles suspended but does not create the repulsive force described in DLVO theory.

D. Density difference

Density differences affect:

• Sedimentation

• Creaming

as explained by Stokes’ law, but it is unrelated to electrostatic repulsion between droplets.

GPAT Tip

Remember this simple association:

• DLVO theory = Attraction vs Repulsion

• Repulsion = Electrical double layer

• Attraction = Van der Waals forces

A stable dispersion exists when repulsive forces exceed attractive forces.

3. Which of the following attractive force is considered in the DLVO theory?

A. Osmotic pressure
B. Electrostatic force
C. Van der Waals force
D. Hydrogen bonding

Answer: C. Van der Waals force

According to the DLVO theory, the stability of colloidal dispersions and emulsions depends on the balance between:

1. Attractive Van der Waals forces

2. Repulsive electrostatic forces (electrical double layer)

The Van der Waals force is the primary attractive force considered in DLVO theory. These forces pull particles or droplets toward each other and may lead to:

• Flocculation

• Aggregation

• Coalescence

if not opposed by sufficient electrostatic repulsion.

Why Other Options Are Incorrect

A. Osmotic pressure

Osmotic pressure is related to solvent movement across semipermeable membranes and is not one of the principal forces in DLVO theory.

B. Electrostatic force

Electrostatic force in DLVO theory is mainly repulsive, arising from the electrical double layer around particles.

The question asks specifically for the attractive force.

D. Hydrogen bonding

Hydrogen bonding may contribute to intermolecular interactions in some systems, but it is not the primary attractive force described in classical DLVO theory.

Exam Tip

Memorize the DLVO theory as

• V = Van der Waals = Attraction

• E = Electrical double layer = Repulsion

A colloidal system remains stable when:

Repulsive force > Attractive force

Frepulsive > Fattractive

4. Monomolecular adsorption theory of emulsification says that emulsifying agents:

A. Increase zeta potential only
B. Increase density of external phase
C. Form rigid films around globules
D. Reduce interfacial tension by forming a monolayer

Answer: D. Reduce interfacial tension by forming a monolayer

According to the Monomolecular Adsorption Theory, emulsifying agents orient themselves at the oil–water interface and form a single molecular layer (monolayer) around dispersed droplets.

This monolayer:

• Reduces interfacial tension

• Facilitates dispersion of one liquid into another

• Helps stabilize the emulsion

Surface-active agents (surfactants) such as soaps and detergents commonly act by this mechanism.

Why Other Options Are Incorrect

A. Increase zeta potential only

Some emulsifying agents may increase zeta potential, producing electrostatic repulsion, but this is not the main basis of monomolecular adsorption theory.

The key concept is:

• Adsorption at interface

• Reduction of interfacial tension

B. Increase density of external phase

Density modification is unrelated to monomolecular adsorption theory.

Density differences mainly influence:

• Creaming

• Sedimentation

rather than emulsification mechanism.

C. Form rigid films around globules

Formation of a rigid or multimolecular film is explained by:

• Multimolecular adsorption theory

• Film formation theory

using hydrophilic colloids such as acacia or gelatin.

Monomolecular theory specifically involves a single molecular layer, not a rigid thick film.

Exam Tip

Quick comparison of emulsification theories:

• Theory Main Mechanism

• Monomolecular adsorption Monolayer formation & reduced interfacial tension

• Multimolecular adsorption Thick flexible film around droplets

• Solid particle adsorption Solid particles form a protective barrier

• DLVO theory Balance of attractive & repulsive forces

Important keyword:

“Surfactant = Monolayer = Reduced interfacial tension."

γo/w​↓

5. Which agent acts by monomolecular adsorption?

A. Bentonite
B. Gelatin
C. Acacia
D. Tweens

Answer: D. Tweens

Tween agents are surface-active agents (surfactants) that stabilize emulsions by the monomolecular adsorption theory.

They adsorb at the oil–water interface to form a monolayer. Thereby, reducing interfacial tension promotes emulsion stability.

Examples are:

• Tween 20

• Tween 80

These are commonly used nonionic emulsifying agents in pharmaceutical emulsions.

Why Other Options Are Incorrect

A. Bentonite

Bentonite acts mainly by the solid particle adsorption theory.

Fine solid particles accumulate at the interface and form a protective mechanical barrier around droplets.

B. Gelatin

Gelatin is a hydrophilic colloid that stabilizes emulsions by forming a multimolecular film around droplets.

It does not act by monomolecular adsorption.

C. Acacia

Acacia also acts mainly by multimolecular adsorption (film formation).

It forms a strong, flexible protective film around dispersed globules.

EXAM Tip

Remember this shortcut:

• Emulsifying Agent Main Theory

• Tweens / Spans Monomolecular adsorption

• Acacia / Gelatin Multimolecular film

• Bentonite / Veegum Solid particle adsorption

Memory trick:

“Surfactants form single layers.”

6. Multimolecular adsorption theory states the formation of:

A. Monolayer film
B. Electrical double layer only
C. Multilayer hydrophobic coating
D. Hydrated lyophilic film around droplets

Answer: D. Hydrated lyophilic film around droplets

According to the Multimolecular Adsorption Theory, hydrophilic colloids (lyophilic colloids) such as:

• Acacia

• Gelatin

• Tragacanth

form a thick hydrated multimolecular film around dispersed droplets.

This film:

• Prevents coalescence

• Provides mechanical stability

• Enhances emulsion stability

The protective layer is lyophilic and hydrated, which is the key feature of this theory.

Why Other Options Are Incorrect

A. Monolayer film

A monolayer film is characteristic of the Monomolecular Adsorption Theory, mainly produced by surfactants such as:

• Tween

• Spans

B. Electrical double layer only

Electrical double layer formation is related to DLVO theory and electrostatic stabilization, not multimolecular adsorption theory.

C. Multilayer hydrophobic coating

The film formed is actually hydrophilic (lyophilic) and hydrated, not hydrophobic.

This hydrated character helps stabilize the emulsion.

Exam Tip

Memory Tip:

• Theory Main Feature

• Monomolecular adsorption Single molecular layer

• Multimolecular adsorption Thick hydrated lyophilic film

• Solid particle adsorption Solid particle barrier

• DLVO theory Electrostatic repulsion vs Van der Waals attraction

Memory trick:

“Hydrophilic colloids form hydrated films.”

7. Which emulsifying agent stabilizes an emulsion by multimolecular adsorption?

A. Span 80
B. Acacia
C. Sodium lauryl sulfate
D. Magnesium hydroxide

Answer: B. Acacia

Acacia stabilizes emulsions by the Multimolecular Adsorption Theory.

Acacia is a hydrophilic colloid that forms a:

• Thick

• Hydrated

• Multimolecular protective film

around dispersed droplets, preventing coalescence and improving emulsion stability.

Why Other Options Are Incorrect

A. Span 80

Span 80 is a surface-active agent (surfactant).

It acts mainly by:

• Monomolecular adsorption

• Reduction of interfacial tension

not by multimolecular film formation.

C. Sodium lauryl sulfate

Sodium lauryl sulfate is also a surfactant acting by

• Monomolecular adsorption theory

It forms a monolayer at the interface.

D. Magnesium hydroxide

Magnesium hydroxide is not a typical multimolecular film-forming emulsifying agent.

Finely divided solids may sometimes stabilize emulsions by solid particle adsorption, but magnesium hydroxide is not the standard answer here.

Exam Tip

Remember these classic associations:

• Agent Type Example Theory

• Surfactants: Tween, Span, SLS Monomolecular adsorption

• Hydrophilic colloids: Acacia, Gelatin Multimolecular adsorption

• Finely divided solids: Bentonite, Veegum Solid particle adsorption

Memory Trick:

“Acacia forms a hydrated protective film.”

8. Name the film formed in the multimolecular adsorption theory

A. Crystalline
B. Electrically neutral
C. Hydrated and flexible
D. Weak and non-hydrated

Answer: C. Hydrated and flexible

In the Multimolecular Adsorption Theory, hydrophilic colloids such as

• Acacia

• Gelatin

form a hydrated, flexible, multimolecular film around dispersed droplets.

This film:

• Protects droplets from coalescence

• Provides mechanical stability

• Enhances emulsion stability

The hydrated nature of the film is very important because it improves compatibility with the continuous aqueous phase.

Why Other Options Are Incorrect

A. Crystalline

The protective film is colloidal and hydrated, not crystalline.

Crystalline structures are not involved in this emulsification mechanism.

B. Electrically neutral

The theory mainly emphasizes the formation of a hydrated protective film, not electrical neutrality.

Electrostatic effects are more closely associated with DLVO theory.

D. Weak and non-hydrated

The film is actually

• Strong enough to prevent coalescence

• Hydrated

• Flexible

Non-hydrated films would not provide effective stabilization.

Exam Tip

Key phrase to memorize:

“Hydrophilic colloids form hydrated flexible films.”

Remember association:

• Theory Film Type

• Monomolecular adsorption Thin monolayer

• Multimolecular adsorption Hydrated flexible film

• Solid particle adsorption Rigid particulate barrier

9. Finely divided solids have the property to stabilize emulsions by:

A. Causing coalescence
B. Increasing density
C. Reducing viscosity
D. Forming a mechanical barrier at the interface

Answer: D

Correct Answer: D. Forming a mechanical barrier at the interface

Finely divided solids stabilize emulsions according to the Solid Particle Adsorption Theory.

Examples include:

• Bentonite

• Magnesium hydroxide

• Veegum

These finely divided particles adsorb at the oil–water interface and form a rigid mechanical barrier around droplets. This barrier prevents:

• Coalescence

• Aggregation of droplets

thereby increasing emulsion stability.

Why Other Options Are Incorrect

A. Causing coalescence

Coalescence means fusion of droplets, which leads to emulsion breakdown.

Emulsifying agents work to prevent coalescence, not promote it.

B. Increasing density

Density changes may influence creaming or sedimentation but are not the primary stabilization mechanism of finely divided solids.

C. Reducing viscosity

In many cases, stabilizers actually increase viscosity to improve stability.

The key mechanism here is interfacial barrier formation, not viscosity reduction.

Exam Tip

Remember emulsification theories:

• Theory Mechanism Common Agents

• Monomolecular adsorption Monolayer formation Tween, Span

• Multimolecular adsorption Hydrated flexible film Acacia, Gelatin

• Solid particle adsorption Mechanical barrier Bentonite, Veegum

Memory trick:

“Fine solids form a rigid shield around droplets.”

10. Which one acts as a solid particle emulsifying agent?

A. Ethanol
B. Tween 80
C. Bentonite
D. Propylene glycol

Answer: C. Bentonite

Bentonite acts as a solid particle emulsifying agent.

According to the Solid Particle Adsorption Theory, finely divided solid particles adsorb at the oil–water interface and form a protective mechanical barrier around droplets, preventing coalescence and improving emulsion stability.

Bentonite is a classic example used in pharmaceutical emulsions.

Why Other Options Are Incorrect

A. Ethanol

Ethanol is mainly used as:

• Solvent

• Co-solvent

• Preservative aid

It is not a solid particle emulsifying agent.

B. Tween 80

Tween 80 is a surfactant that acts by:

• Monomolecular adsorption

• Reduction of interfacial tension

not by solid particle adsorption.

D. Propylene glycol

Propylene glycol is commonly used as:

• Solvent

• Humectant

• Co-solvent

It does not stabilize emulsions via solid particle adsorption.

Exam Tip

Classification:

• Emulsifying Agent Type of Stabilization

• Tween / Span Monomolecular adsorption

• Acacia / Gelatin Multimolecular adsorption

• Bentonite / Veegum Solid particle adsorption

Memory trick:

“Bentonite builds a solid protective wall.”

11. Which one stabilizes Pickering emulsions?

A. Alcohols
B. Hydrophilic colloids
C. Synthetic surfactants
D. Finely divided solid particles

Answer: D. Finely divided solid particles

Pickering emulsions are emulsions stabilized by finely divided solid particles adsorbed at the oil–water interface.

Examples of such stabilizing agents include:

• Bentonite

• Veegum

• Magnesium hydroxide

• Silica particles

These particles form a rigid mechanical barrier around droplets and prevent coalescence.

Why Other Options Are Incorrect

A. Alcohols

Alcohols mainly act as:

• Solvents

• Co-solvents

• Preservatives (some cases)

They do not stabilize Pickering emulsions.

B. Hydrophilic colloids

Hydrophilic colloids such as:

• Acacia

• Gelatin

stabilize emulsions by multimolecular adsorption, not Pickering stabilization.

C. Synthetic surfactants

Synthetic surfactants like:

• Tween 80

• Sodium lauryl sulfate

act mainly by monomolecular adsorption and reduction of interfacial tension.

Exam Tip

Important association:

• Emulsion Type Stabilizing Agent

• Pickering emulsion Finely divided solid particles

• Conventional surfactant emulsion Surface-active agents

Memory trick:

“Pickering emulsions pick solid particles for stability.”

12. In the film emulsification theory, emulsifying agents act on:

A. On Electrical barrier only
B. On sediment droplets
C. On micelles in continuous phase only
D. On a coherent interfacial film around droplets

Answer: D

Correct Answer: D. On a coherent interfacial film around droplets

According to the Film Emulsification Theory, emulsifying agents form a coherent, continuous interfacial film around dispersed droplets.

This protective film:

• Surrounds the droplets

• Prevents coalescence

• Improves emulsion stability

The film acts as a mechanical barrier between dispersed globules.

Common film-forming emulsifying agents include:

• Acacia

• Gelatin

Why Other Options Are Incorrect

A. On electrical barrier only ❌

Electrical barriers are mainly related to:

• Electrical double layer

• Zeta potential

• DLVO theory

Film theory specifically emphasizes formation of an interfacial film.

B. On sediment droplets ❌

Sedimentation is related to suspensions and density differences, not the primary mechanism of emulsification film theory.

C. On micelles in continuous phase only ❌

Micelles may form in surfactant systems above critical micelle concentration, but film emulsification theory focuses on the interfacial film surrounding droplets, not only micelles in bulk phase.

Exam Tip

Remember the major emulsification theories:

• Theory Main Stabilizing Mechanism

• Monomolecular adsorption Monolayer at interface

• Multimolecular adsorption Hydrated flexible film

• Film theory Coherent interfacial film

• Solid particle adsorption Mechanical particulate barrier

Memory trick:

“Film theory = protective coat around droplets.”

13. Which one is NOT an emulsion stabilization mechanism?

A. Electrostatic repulsion
B. Formation of interfacial film
C. Reduction of interfacial tension
D. Increase in gravitational force

Answer: D. Increase in gravitational force

An increase in gravitational force does not stabilize an emulsion. Instead, it promotes instability phenomena such as:

• Creaming

• Sedimentation

• Phase separation

A greater gravitational effect increases the tendency of droplets to separate based on density differences.

Why Other Options Are Correct Stabilization Mechanisms

A. Electrostatic repulsion

Electrostatic repulsion arises from the electrical double layer around droplets.

It prevents droplets from coming together and is explained by DLVO theory.

B. Formation of interfacial film

Emulsifying agents such as

• Acacia

• Gelatin

form a protective interfacial film around droplets, preventing coalescence.

C. Reduction of interfacial tension

Surfactants such as:

• Tween 80

• Sodium lauryl sulfate

reduce interfacial tension and facilitate stable emulsion formation.

γo/w​↓

Exam Tip

Stable emulsions are favored by:

• Low interfacial tension

• Protective interfacial films

• Electrostatic repulsion

• Increased viscosity

Instability increases with:

• Gravity effects

• Coalescence

• Creaming

• Flocculation

Memory trick:

“Gravity separates; emulsifiers stabilize.”

14. Creaming in emulsions is

A. Globules fusion
B. Permanent phase separation
C. Chemical degradation of emulsifier
D. Reversible separation of dispersed phase

Answer: D

Correct Answer: D. Reversible separation of dispersed phase

Creaming is the reversible separation of the dispersed phase in an emulsion due to density differences between the two phases.

In creaming:

• Droplets concentrate either at the top or bottom

• The droplets do not fuse together

• Shaking can usually redistribute the droplets uniformly

Thus, creaming does not destroy the emulsion permanently.

Why Other Options Are Incorrect

A. Globules fusion

Fusion of globules is called coalescence, not creaming.

Coalescence leads to larger droplets and eventual emulsion breakdown.

B. Permanent phase separation

Permanent phase separation is known as:

• Cracking

• Breaking

This is irreversible, unlike creaming.

C. Chemical degradation of emulsifier

Chemical degradation may destabilize emulsions but is not the definition of creaming.

Creaming is mainly a physical instability caused by density differences.

Exam Tip

Important distinction:

• Phenomenon Reversible or Irreversible

• Creaming Reversible

• Flocculation Reversible

• Coalescence Irreversible

• Cracking/Breaking Irreversible

Memory trick:

“Creaming can be corrected by shaking.”

15. The reason for creaming in an emulsion is

A. Oil oxidation
B. Emulsifier Hydrolysis
C. Increase in zeta potential
D. Difference in density between phases

Answer: D. Difference in density between phases

Creaming occurs because of the difference in density between the dispersed phase and the continuous phase of an emulsion.

• If oil droplets are lighter than the aqueous phase, they rise upward (upward creaming).

• If dispersed particles are heavier, they settle downward (sedimentation).

Creaming is explained by Stokes’ law.

v=2r²(d₁−d₂)g/9η

From the equation:

• Greater density difference (d1 - d2) = faster creaming

• Larger droplet size = faster creaming

• Higher viscosity = slower creaming

Why Other Options Are Incorrect

A. Oil oxidation

Oil oxidation causes

• Rancidity

• Off-odor

• Chemical degradation

but it is not the primary cause of creaming.

B. Emulsifier hydrolysis

Hydrolysis of emulsifiers may destabilize emulsions chemically, but creaming mainly results from density differences and gravitational separation.

C. Increase in zeta potential

Higher zeta potential generally improves emulsion stability by increasing electrostatic repulsion between droplets.

It helps prevent aggregation rather than causing creaming.

GPAT Tip

Important point:

• Creaming is reversible

• Coalescence/cracking is irreversible

Ways to reduce creaming:

• Reduce droplet size

• Increase viscosity

• Minimize density difference

Memory trick:

“Density difference drives creaming.”

16. In Stokes’ law, the creaming rate is directly proportional to:

A. Medium Viscosity
B. Temperature
C. Radius of globules squared
D. Density of dispersed phase only

Answer: C. Radius of globules squared

According to Stokes’ law, the creaming or sedimentation rate of dispersed globules is

From the equation: v ∝ r²

Thus, the creaming rate is directly proportional to the square of the globule radius.

Larger droplets cream much faster than smaller droplets do.

Why Other Options Are Incorrect

A. Medium viscosity

The creaming rate is inversely proportional to viscosity.

Higher viscosity slows down globule movement and reduces creaming.

B. Temperature

Temperature is not directly included in the classical Stokes’ law equation, though it may indirectly affect viscosity.

D. Density of dispersed phase only

The law depends on the difference in density between dispersed and continuous phases, not the dispersed phase density alone.

GPAT Tip

To reduce creaming:

• Reduce globule size

• Increase viscosity

• Minimize density difference

Memory trick:

“Big droplets cream faster.”

Very high-yield Stokes’ law point: Creaming rate ∝ r²

17. The creaming rate decreases if:

A. Particle size increases
B. Temperature increases
C. Density difference increases
D. Viscosity of external phase increases

Answer: D. Viscosity of the external phase increases

According to Stokes’ law:

v=2r²(d₁−d₂)g/9η

where:

• (v) = creaming rate

• (r) = radius of globules

• (d1 - d2) = density difference

• η (eta) = viscosity of external phase

The equation shows that the creaming rate is inversely proportional to viscosity.

Therefore:

• Higher viscosity = slower droplet movement

• Lower viscosity = faster creaming

Hence, increasing the viscosity of the external phase decreases creaming.

Why Other Options Are Incorrect

• A. Particle size increases The creaming rate is directly proportional to the square of the

  • particle radius.

  • Larger particles cream faster, not slower.

• B. Temperature increases

  • An increase in temperature generally lowers viscosity, which may actually increase the creaming rate.

• C. Density difference increases

  • A greater density difference between phases increases gravitational separation and therefore increases the creaming rate.

GPAT Tip

Ways to minimize creaming:

• Decrease globule size

• Increase viscosity

• Reduce density difference

Common viscosity enhancers:

• Acacia

• Tragacanth

• Methylcellulose

Memory trick:

“Thicker medium = slower creaming.”

18. The equation associated with the creaming of emulsions is:

A. Arrhenius equation
B. Stokes’ law
C. Henderson equation
D. Noyes–Whitney equation

Answer: B. Stokes’ law

The phenomenon of creaming in emulsions is explained by Stokes’ law. It describes the settling or rising velocity of dispersed particles/globules under gravity.

This equation shows that cream increases with

• Larger globule size

• Greater density difference

and decreases with:

• Higher viscosity

Why Other Options Are Incorrect

A. Arrhenius equation

The Arrhenius equation relates:

• Temperature

• Rate constant of chemical reactions

It is not related to creaming of emulsions.

C. Henderson equation

The Henderson–Hasselbalch equation is used for:

• Buffer calculations

• pH determination

not emulsion stability.

D. Noyes–Whitney equation

The Noyes-Whitney equation describes

• Drug dissolution rate

not creaming behavior.

Exam Tip

Very important association:

• Equation Application

• Stokes’ law Creaming / sedimentation

• Arrhenius equation Reaction kinetics

• Henderson–Hasselbalch Buffer pH

• Noyes–Whitney Dissolution rate

Memory trick:

“Stokes controls settling and creaming.”

19. Coalescence means

A. Reduction in droplet size
B. Sedimentation of particles
C. Reversible aggregation of droplets
D. Fusion of droplets to form larger droplets

Answer: D. Fusion of droplets to form larger droplets

Coalescence is the process in which small dispersed droplets merge or fuse together to form larger droplets.

This occurs when the protective interfacial film around droplets breaks down, leading to emulsion instability.

Coalescence may eventually result in:

• Cracking

• Breaking of emulsion

• Permanent phase separation

Why Other Options Are Incorrect

A. Reduction in droplet size

Coalescence causes an increase in droplet size, not a reduction.

• B. Sedimentation of particles

  • Sedimentation refers to the settling of heavier particles under gravity, mainly seen in suspensions.

It is different from droplet fusion in emulsions.

• C. Reversible aggregation of droplets

  • Reversible aggregation without fusion is called flocculation.

• In flocculation:

  • Droplets cluster together

  • Individual droplet identity remains intact

In coalescence, droplets permanently fuse.

GPAT Tip

Important distinction:

• Phenomenon Nature

• Flocculation Reversible Aggregation

• Coalescence Fusion of Droplets

• Creaming Reversible Phase Concentration

• Cracking Complete Irreversible Separation

Memory trick:

“Coalescence = Combine into larger droplets.”

20. Cracking (breaking) of emulsion means

A. Increase in viscosity
B. Temporary creaming
C. Reversible separation
D. Irreversible phase separation

Answer: D. Irreversible phase separation

Cracking or breaking of an emulsion refers to the irreversible separation of the emulsion into two distinct phases.

In cracked emulsions:

• The dispersed droplets coalesce completely

• The original emulsion cannot be restored by simple shaking

• The emulsifying film is permanently destroyed

This represents complete emulsion failure.

Why Other Options Are Incorrect

• A. Increase in viscosity

  • An increase in viscosity generally improves emulsion stability and reduces creaming.

It is not the definition of cracking.

• B. Temporary creaming

  • Creaming is a reversible instability where droplets concentrate at the top or bottom but remain separate.

Shaking can usually redisperse the emulsion.

C. Reversible separation

Cracking is irreversible, not reversible.

Reversible separation is characteristic of creaming or flocculation.

21. Which instability precedes the emulsion's cracking?

A. Creaming
B. Flocculation
C. Coalescence
D. Ostwald ripening

Answer: C. Coalescence

Cracking (breaking) of an emulsion is usually preceded by coalescence.

In coalescence:

• The protective film around droplets breaks down

• Small droplets fuse to form larger droplets

• Continuous fusion ultimately causes complete phase separation (cracking)

Thus, coalescence is a major step leading to irreversible emulsion breakdown.

Why Other Options Are Incorrect

• A. Creaming

  • Creaming is only a reversible concentration of droplets due to density differences.

  • Although prolonged creaming may increase the chance of coalescence, creaming itself does not directly mean cracking.

• B. Flocculation

  • Flocculation is a reversible aggregation where droplets remain distinct.

  • No fusion occurs in flocculation.

• D. Ostwald ripening

  • Ostwald ripening involves the growth of larger droplets at the expense of smaller ones due to solubility differences.

  • It may destabilize emulsions over time, but it is not the classic immediate precursor to cracking.

GPAT Tip

The sequence of emulsion instability is often remembered as

Creaming = Coalescence = Cracking

• Instability Key Feature

• Creaming Droplets concentrate

• Flocculation Loose aggregation

• Coalescence Droplet fusion

• Cracking Permanent separation

Memory trick:

“Fusion of droplets finally breaks the emulsion.”

22. Phase inversion means:

A. Hydrolysis of emulsifier
B. Creaming of dispersed phase
C. Change from o/w to w/o or vice versa
D. Conversion of emulsion into suspension

Answer: C. Change from o/w to w/o or vice versa

Phase inversion is the process in which an emulsion changes from:

• Oil-in-water (o/w) to water-in-oil (w/o)

or

• Water-in-oil (w/o) to oil-in-water (o/w)

This occurs when the dispersed phase and continuous phase interchange.

Common causes include:

• Change in phase volume ratio

• Addition of electrolytes

• Temperature change

• Change in emulsifying agent

Why Other Options Are Incorrect

• A. Hydrolysis of emulsifier

  • Hydrolysis may degrade the emulsifier and destabilize the emulsion, but it does not define phase inversion.

• B. Creaming of dispersed phase

  • Creaming is only an upward or downward movement of droplets due to density differences.

  • It does not involve an interchange of internal and external phases.

• D. Conversion of emulsion into suspension

  • An emulsion contains liquid droplets dispersed in another liquid, whereas a suspension contains solid particles dispersed in a liquid.

  • Phase inversion does not convert an emulsion into a suspension.

GPAT Tip 🎯

Remember:

• Emulsion Type Dispersed Phase Continuous Phase

• o/w Oil Water

• w/o Water Oil

Phase inversion = exchange of phases

Memory trick:

“Internal phase becomes external.”

23. Which one induces phase inversion?

A. Addition of preservatives
B. Low temperature only
C. Reduction in globule size only
D. Excessive internal phase volume

Answer: D. Excessive internal phase volume

Phase inversion occurs when an emulsion changes from

• Oil-in-water (o/w) to water-in-oil (w/o)

or vice versa.

One of the most common causes is an excessive volume of the internal (dispersed) phase. When the dispersed phase becomes too concentrated. The existing continuous phase can no longer accommodate it. This causes the phases to interchange.

Why Other Options Are Incorrect

A. Addition of preservatives

Preservatives are added to prevent microbial growth. Generally, they do not cause phase inversion.

B. Low temperature only

Temperature changes can influence some emulsions. Especially those containing nonionic surfactants. But “low temperature only” is not a standard that causes phase inversion.

C. Reduction in globule size only

Smaller globule size usually improves emulsion stability by reducing creaming and coalescence.

It does not directly cause inversion.

Exam Tip

Important causes of phase inversion:

• Cause Effect

• Excess internal phase volume Phase interchange

• Temperature change Inversion in nonionic emulsions

• Electrolytes Alter emulsifier behavior

Memory trick:

“Too much dispersed phase flips the emulsion.”

24. An electrolyte destabilizes the stable emulsion by:

A. Increase in viscosity
B. Increase in hydration
C. Reduce interfacial tension
D. Compress the electrical double layer

Answer: D. Compress the electrical double layer

Electrolytes destabilize emulsions by compressing the electrical double layer around dispersed droplets.

DLVO theory states that stable emulsions are maintained by electrostatic repulsion between similarly charged droplets. When electrolytes are added:

• The repulsive force decreases

• Zeta potential decreases

• Counterions neutralize surface charges

• The electrical double layer becomes compressed

As a result, droplets come closer together, leading to:

• Flocculation

• Coalescence

• Cracking

Why Other Options Are Incorrect

• A. Increase in viscosity

  • Increasing viscosity generally improves emulsion stability by reducing droplet movement and creaming.

• B. Increase in hydration

  • Hydration of protective colloids usually stabilizes emulsions rather than destabilizing them.

• C. Reduce interfacial tension

  • Reduction in interfacial tension usually favors emulsion formation and stability.

Electrolytes mainly destabilize by affecting electrostatic repulsion.

Exam Tip

Important association:

• Factor Effect on Emulsion

• High zeta potential Stable emulsion

• Electrolyte addition Double-layer compression

• Reduced repulsion Flocculation/coalescence

Memory trick:

“Electrolytes shrink the electrical shield.”

Electrolyte=↓Zeta Potential=↓Repulsion

25. The energy barrier that prevents coalescence in DLVO theory is due to:

A. Osmotic pressure
B. Gravitational force
C. Brownian motion
D. Electrostatic repulsion

Answer: D

Correct Answer: D. Electrostatic repulsion

According to DLVO theory, the energy barrier preventing droplets or particles from coming together is produced by electrostatic repulsion arising from the electrical double layer surrounding the dispersed droplets.

When two similarly charged droplets approach each other:

• Their electrical double layers repel

• An energy barrier is created

• Coalescence is prevented

If this repulsive barrier becomes weak, droplets can aggregate and fuse.

Why Other Options Are Incorrect

• A. Osmotic pressure

  • Osmotic pressure is related to solvent movement across semipermeable membranes and is not the primary stabilizing energy barrier in DLVO theory.

• B. Gravitational force

  • Gravity contributes to:

    • Creaming

    • Sedimentation

but not to the energy barrier preventing coalescence.

• C. Brownian motion

  • Brownian motion causes the random movement of particles but does not create the electrostatic energy barrier responsible for colloidal stability.

GPAT Tip

DLVO theory balances two major forces:

• Force Nature

• Van der Waals force Attractive

• Electrostatic repulsion Repulsive

Stable emulsion condition:

Frepulsive > Fattractive

Memory trick:

“Electrical repulsion builds the protective energy wall.”

26. Which of the following forms a w/o emulsion?

A. Acacia
B. Tween 80
C. Span 80
D. Sodium lauryl sulfate

Answer: C. Span 80

Span 80 is a lipophilic (oil-soluble) surfactant with a low HLB value, so it preferentially forms water-in-oil (w/o) emulsions.

Low HLB emulsifiers favor

• Oil as the continuous phase

• Water as the dispersed phase

Why Other Options Are Incorrect

A. Acacia

Acacia is a hydrophilic colloid that generally forms oil-in-water (o/w) emulsions.

B. Tween 80

Tween 80 has a high HLB value and is hydrophilic, so it forms o/w emulsions.

D. Sodium lauryl sulfate

Sodium lauryl sulfate is a hydrophilic surfactant and also favors o/w emulsions.

Exam Tip

Important HLB rule:

• HLB Value Type of Emulsion Favored

• Low HLB (3–6) w/o emulsion

• High HLB (8–18) o/w emulsion

Examples:

• Emulsifier Emulsion Type

• Span 80 w/o

• Tween 80 o/w

Memory trick:

“Span stays in oil.”

27. Hydrophilic colloids stabilize emulsions by:

A. Producing sedimentation
B. Increasing interfacial tension
C. Decreasing viscosity drastically
D. Forming hydrated multimolecular films

Answer: D. Forming hydrated multimolecular films

Hydrophilic colloids stabilize emulsions by forming hydrated multimolecular protective films around dispersed droplets.

Examples:

• Acacia

• Gelatin

• Tragacanth

These agents act according to the multimolecular adsorption theory.

The hydrated film:

• Prevents coalescence

• Enhances emulsion stability

• Increases viscosity moderately

• Provides mechanical stability

Why Other Options Are Incorrect

• A. Producing sedimentation

  • Sedimentation is an instability phenomenon and is not a stabilization mechanism for emulsions.

• B. Increasing interfacial tension

  • Stable emulsions require a reduction of interfacial tension, not increase.

• C. Decreasing viscosity drastically

  • Hydrophilic colloids usually increase viscosity, which helps reduce creaming and improve stability.

Exam Tip

Remember:

• Emulsifying Agent Type Mechanism

• Surfactants Monomolecular film

• Hydrophilic colloids Hydrated multimolecular film

• Finely divided solids Mechanical barrier

Memory trick:

“Hydrophilic colloids hold water and form protective hydrated films.”

28. Which one is reversible after shaking?

A. Creaming
B. Cracking
C. Coalescence
D. Phase inversion

Answer: A. Creaming

Creaming is a reversible instability of emulsions. The dispersed droplets concentrate at the top due to density differences.

The droplets do not fuse. The original emulsion can be restored by simple shaking.

Why Other Options Are Incorrect

• B. Cracking

  • Cracking (breaking) is an irreversible separation of phases.

  • Once cracking occurs, shaking cannot restore the emulsion.

• C. Coalescence

  • Coalescence involves the fusion of droplets into larger droplets.

  • This process is generally irreversible and may lead to cracking.

• D. Phase inversion

  • Phase inversion involves the conversion of

    • o/w → w/o
      or

    • w/o → o/w

It is not corrected simply by shaking.

29. A pharmaceutical emulsion with irreversible separation into two layers is due to:

A. Creaming
B. Breaking
C. Flocculation
D. Ostwald ripening

Answer: B. Breaking

Breaking (cracking) of an emulsion is the irreversible separation of the emulsion into two distinct layers.

In this condition:

• Droplets coalesce completely

• The emulsifying film is destroyed

• Simple shaking cannot restore the emulsion

Thus, the emulsion becomes permanently unstable.

Why Other Options Are Incorrect

• A. Creaming

  • Creaming is a reversible concentration of dispersed droplets due to density differences.

  • The emulsion can be restored by shaking.

• C. Flocculation

  • Flocculation is the reversible aggregation of droplets without fusion.

  • Individual droplets remain separate.

• D. Ostwald ripening

  • Ostwald ripening is the growth of larger droplets at the expense of smaller droplets due to differences in solubility.

  • It contributes to instability gradually but does not directly define irreversible two-layer separation.

30. Which one is best to prevent coalescence?

A. Increase in globule interaction
B. Increase in density difference
C. Reducing viscosity to a minimum
D. Formation of strong interfacial film

Answer: D. Formation of strong interfacial film

Coalescence occurs when dispersed droplets fuse together to form larger droplets.
A strong interfacial film around droplets prevents direct contact and fusion, thereby preventing coalescence.

Such films are formed by emulsifying agents like

• Acacia

• Gelatin

These agents stabilize emulsions by forming protective hydrated films around droplets.

Why Other Options Are Incorrect

• A. Increase in globule interaction

  • Greater interaction between droplets increases the chance of collision and fusion. It promotes coalescence rather than preventing it.

• B. Increase in density difference

  • Higher density difference increases:

    • Creaming

    • Sedimentation

which may indirectly increase instability.

• C. Reducing viscosity to a minimum

  • Lower viscosity allows droplets to move more freely. It increases collisions and promotes coalescence.

  • Higher viscosity generally improves stability.

Exam Tip

Factors preventing coalescence:

• Strong interfacial film

• High zeta potential

• Adequate viscosity

• Small droplet size

Memory trick:

“Strong film stops droplet fusion.”

31. Under which condition does an emulsion become unstable in DLVO theory?

A. Very high viscosity
B. Density difference becomes zero
C. Attractive forces exceed repulsive forces
D. Repulsive forces exceed attractive forces

Answer: C. Attractive forces exceed repulsive forces

According to DLVO theory, the stability of emulsions and colloidal dispersions depends on the balance between:

• Attractive Van der Waals forces

• Repulsive electrostatic forces (electrical double layer)

An emulsion becomes unstable when the attractive forces become stronger than the repulsive forces. In that situation:

• Droplets come closer together

• Flocculation and coalescence occur

• Cracking may eventually result

Fattractive > Frepulsive

Why Other Options Are Incorrect

• A. Very high viscosity

  • High viscosity usually improves emulsion stability by slowing droplet movement and reducing collisions.

• B. Density difference becomes zero

  • A lower density difference actually reduces creaming and generally favors stability.

• D. Repulsive forces exceed attractive forces

  • This condition represents a stable emulsion. This is due to droplets repelling each other and resisting aggregation.

Frepulsive > Fattractive

Exam Tip

DLVO theory summary:

• Force Effect

• Van der Waals attraction Destabilization

• Electrostatic repulsion Stabilization

Memory trick:

“Attraction dominates → instability begins.”

32. A decreased zeta potential of emulsion droplets:

A. Promote coalescence
B. Convert o/w to w/o emulsion
C. Prevent creaming completely
D. Increase electrostatic repulsion

Answer: A. Promote coalescence

Zeta potential represents the magnitude of electrical charge around emulsion droplets.

When zeta potential decreases:

• Electrostatic repulsion between droplets decreases

• Droplets can approach each other more easily

• Flocculation and coalescence become more likely

Thus, a decreased zeta potential promotes emulsion instability.

↓Zeta Potential = ↓Repulsion = ↑Coalescence

Why Other Options Are Incorrect

• B. Convert o/w to w/o emulsion

  • Conversion between o/w and w/o emulsions is called phase inversion. This depends mainly on:

    • Phase volume ratio

    • Emulsifier type

    • Temperature

not directly on the zeta potential.

• C. Prevent creaming completely

  • Zeta potential mainly affects droplet interaction and aggregation, not density-driven creaming.

  • Creaming depends on:

    • Density difference

    • Droplet size

    • Viscosity

• D. Increase electrostatic repulsion

  • A decrease in zeta potential actually reduces electrostatic repulsion.

  • Higher zeta potential gives greater stability.

Exam Tip

Important concept:

• Zeta Potential Emulsion Stability

• High Stable

• Low Coalescence likely

Memory trick:

“Low zeta = weak electrical shield.”

33. Which one for Pickering emulsions is CORRECT?

A. Interfacial tension becomes zero
B. Stability depends only on viscosity
C. Stabilization occurs by surfactant micelles
D. Solid particles adsorb irreversibly at the interface.

Answer: D. Solid particles adsorb irreversibly at the interface

Pickering emulsion property: stabilization occurs because finely divided solid particles adsorb strongly and almost irreversibly at the oil–water interface.

Examples of finely divided solid particles:

• Bentonite

• Silica

• Veegum

These particles form a rigid mechanical barrier around droplets. This prevents coalescence and improves emulsion stability.

Why Other Options Are Incorrect

• A. Interfacial tension becomes zero

  • Interfacial tension may decrease, but it does not become zero in Pickering emulsions.

  • Complete elimination of interfacial tension is unrealistic.

• B. Stability depends only on viscosity

  • Viscosity contributes to stability, but Pickering emulsions are mainly stabilized by the adsorbed solid particle layer at the interface.

• C. Stabilization occurs by surfactant micelles

  • Pickering emulsions are stabilized by solid particles, not by surfactant micelles.

  • Micellar stabilization is associated with surfactant systems.

Exam Tip

Key feature of Pickering emulsions:

• Stabilizer Mechanism

• Solid particles Mechanical interfacial barrier

Memory trick:

“Pickering emulsions pick particles, not surfactants.”

34. The phase inversion temperature method is related to:

A. Ionic surfactants
B. Nonionic surfactants
C. Solid particle emulsifiers
D. Hydrophilic colloids only

Answer: B

Correct Answer: B. Nonionic surfactants

The Phase Inversion Temperature (PIT) method is mainly associated with nonionic surfactants such as:

• Tween 80

Nonionic surfactants contain polyoxyethylene chains whose hydrophilic character changes with temperature.

At the PIT:

• Hydrophilic and lipophilic properties become balanced

• The emulsion may invert from:

  • o/w → w/o
    or

  • w/o → o/w

This principle is widely used in emulsion formulation.

Why Other Options Are Incorrect

A. Ionic surfactants ❌

Ionic surfactants are less affected by temperature changes in terms of hydrophilic-lipophilic balance.

PIT is mainly characteristic of nonionic surfactants.

C. Solid particle emulsifiers ❌

Solid particle emulsifiers stabilize Pickering emulsions and are not related to PIT behavior.

D. Hydrophilic colloids only ❌

Hydrophilic colloids such as:

• Acacia

• Gelatin

stabilize emulsions by film formation, not by PIT mechanism.

Exam Tip 🎯

Important association:

• Method Related Emulsifier

• PIT method Nonionic surfactants

• Pickering stabilization Solid particles

• Multimolecular film theory Hydrophilic colloids

Memory trick:

“Temperature-sensitive emulsions use nonionic surfactants.”

35. An emulsion has a droplet radius that is doubled. The creaming rate will become ______ according to Stokes’ law.

A. Half
B. Four times
C. Eight times
D. Two times

Answer: B. Four times

According to Stokes’ law:

The creaming rate (v) is directly proportional to the square of the droplet radius: v ∝ r².

If the droplet radius is doubled: (2r)² = 4r²

Therefore, the creaming rate becomes four times greater.

Why Other Options Are Incorrect

• A. Half

  • Doubling the radius increases the creaming rate rather than decreasing it.

• C. Eight times

  • The relationship is with the square of the radius, not the cube.

• D. Two times

  • Creaming rate does not increase linearly with radius; it increases with (r^2).

GPAT Tip 🎯

Very high-yield concept:

Small reduction in droplet size greatly improves emulsion stability.

Memory trick:

“Double radius = fourfold creaming.”

36. If the viscosity of the continuous phase is increased from 1 poise to 2 poise, the the creaming rate will

A. Become half
B. Double
C. Remain unchanged
D. Become four times

Answer: A. Become half

According to Stokes’ law:

The creaming rate (v) is inversely proportional to the viscosity of the continuous phase.

If viscosity increases from v ∝ 1/η,

then v→1/2

So, the creaming rate becomes half.

Why Other Options Are Incorrect

• B. Double

  • Increasing viscosity slows droplet movement rather than increasing creaming.

• C. Remain unchanged

  • Viscosity directly affects the creaming rate according to Stokes’ law.

• D. Become four times

  • There is no square relationship with viscosity.

  • The inverse proportionality is linear.

Memory trick:

“Thicker medium slows creaming.”

37. Which condition causes phase inversion from o/w to w/o emulsion?

A. Reducing globule size
B. Decrease in temperature only
C. Increase in oil phase volume excessively
D. Increase in the water phase beyond the critical volume

Answer: C. Increase in oil-phase volume excessively

An oil-in-water (o/w) emulsion can undergo phase inversion to a water-in-oil (w/o) emulsion if the oil phase volume becomes excessively high.

When the internal (dispersed) oil phase exceeds the critical limit, the system can no longer maintain oil droplets dispersed in water. This result:

• Oil becomes the continuous phase

• Water becomes the dispersed phase

Leading to inversion from o/w → w/o.

Why Other Options Are Incorrect

• A. Reducing globule size

  • Reducing droplet size generally improves emulsion stability and does not directly cause inversion.

• B. Decrease in temperature only

  • Temperature can influence inversion in some nonionic surfactant systems, but “decrease in temperature only” is not the general direct cause here.

• D. Increase in the water phase beyond the critical volume

  • Increasing water phase excessively would favor formation of an o/w emulsion, not conversion to w/o.

Exam Tip

Important rule:

• Excess Internal Phase Result

• Excess oil phase o/w → w/o

• Excess water phase w/o → o/w

Memory trick:

“Whichever phase dominates may become continuous.”

38. Which one best differentiates coalescence from flocculation?

A. Coalescence is reversible
B. Flocculation always leads to cracking
C. Flocculation involves the fusion of droplets
D. Coalescence causes an increase in droplet size permanently

Answer: D

Correct Answer: D. Coalescence causes an increase in droplet size permanently

The key difference between coalescence and flocculation is that:

• In coalescence, droplets fuse together permanently to form larger droplets.

• In flocculation, droplets aggregate loosely but retain their individual identity.

Thus, coalescence results in a permanent increase in droplet size.

Why Other Options Are Incorrect

A. Coalescence is reversible ❌

Coalescence is generally irreversible because droplets permanently fuse.

B. Flocculation always leads to cracking ❌

Flocculation is usually reversible and does not necessarily lead to cracking.

C. Flocculation involves the fusion of droplets ❌

Fusion of droplets occurs in coalescence, not flocculation.

In flocculation, droplets remain separate within aggregates.

Exam Tip 🎯

Important comparison:

• Feature Flocculation Coalescence

• Droplet identity retained Yes No

• Fusion occurs No Yes

• Reversible Usually yes Usually no

• Droplet size permanently increases No Yes

Memory trick:

“Flocs stick; coalesced droplets combine.”

39. A stable emulsion should ideally possess:

A. Weak interfacial film
B. High interfacial tension
C. Large density difference
D. Small uniform globule size

Answer: D. Small uniform globule size

A stable emulsion should ideally have small and uniformly sized globules because

• Smaller droplets cream more slowly

• Uniform size reduces instability

• Smaller globules reduce chances of coalescence

According to Stokes’ law, the creaming rate is proportional to the square of the globule radius.

Thus, reducing droplet size greatly improves emulsion stability.

Why Other Options Are Incorrect

• A. Weak interfacial film

  • A stable emulsion requires a strong protective interfacial film to prevent coalescence.

• B. High interfacial tension

  • High interfacial tension opposes emulsion formation and promotes instability.

  • Stable emulsions require low interfacial tension.

• C. Large density difference

  • A greater density difference increases creaming and phase separation.

  • A lower density difference favors stability.

Exam Tip

Characteristics of stable emulsions:

• Small uniform droplets

• Strong interfacial film

• High zeta potential

• Low interfacial tension

• Adequate viscosity

Memory trick:

“Small uniform globules give stable emulsions.”

40. Which parameter is critical for long-term emulsion stability?

A. Odor of oil phase
B. Color of emulsion
C. Electrokinetic potential
D. Density of container

Answer: C. Electrokinetic potential

The electrokinetic potential (zeta potential) is highly important for long-term emulsion stability.

A high zeta potential produces strong electrostatic repulsion between droplets. This prevents:

• Flocculation

• Coalescence

• Cracking

Thus, emulsions with sufficiently high zeta potential are generally more stable.

↑Zeta Potential→↑Stability

Why Other Options Are Incorrect

• A. Odor of oil phase

  • Odor may indicate oxidation or degradation but is not a direct stability parameter.

• B. Color of emulsion

  • Color has little relation to the electrostatic or physical stability of emulsions.

• D. Density of container

  • Container density does not determine emulsion stability.

  • The important factor is the density difference between emulsion phases, not the container.

Exam Tip

Important stability factors:

• Factor Effect

• High zeta potential Better stability

• Strong interfacial film Prevents coalescence

• High viscosity Reduces creaming

• Small droplet size Improves stability

Memory trick:

“High zeta = strong droplet repulsion.”

Dr. Alok Singh https://www.alokpdf.com/about-me