Rheological properties of emulsions MCQs With Answer

Introduction: Rheological properties of emulsions are central to formulation science in B. Pharm programs, linking viscosity, flow behavior, and viscoelasticity to emulsion stability and performance. Understanding shear-thinning, yield stress, thixotropy, and rheological models (Newtonian, power-law, Herschel-Bulkley) helps predict creaming, coalescence, and drug release. Measurement techniques such as rotational rheometry, cone-and-plate and concentric cylinder methods provide rheograms, flow curves, and oscillatory data (G’ and G”) essential for optimizing surfactants, droplet size, and continuous-phase viscosity. This knowledge guides selection of rheology modifiers and quality control for topical, oral and parenteral emulsions. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is rheology in the context of pharmaceutical emulsions?

• The study of chemical stability of emulsifiers
• The study of flow and deformation behavior of emulsion systems
• The study of microbial contamination in emulsions
• The study of drug-release kinetics only

Correct Answer: The study of flow and deformation behavior of emulsion systems

Q2. Which parameter primarily describes resistance to flow in an emulsion?

• Interfacial tension
• Viscosity
• Density
• Surface charge

Correct Answer: Viscosity

Q3. A Newtonian emulsion shows which of the following behaviors?

• Viscosity decreases with increasing shear rate
• Viscosity increases with increasing shear rate
• Viscosity remains constant irrespective of shear rate
• Viscosity fluctuates unpredictably with shear

Correct Answer: Viscosity remains constant irrespective of shear rate

Q4. Which rheological model describes shear-thinning fluids?

• Newtonian model
• Bingham plastic model
• Power-law (Ostwald-de Waele) model
• Ideal elastic model

Correct Answer: Power-law (Ostwald-de Waele) model

Q5. Yield stress in an emulsion refers to:

• The stress at which droplets begin to coalesce
• The minimum stress required to initiate flow
• The stress needed to break surfactant bonds
• The maximum stress an emulsion can withstand before rupturing

Correct Answer: The minimum stress required to initiate flow

Q6. Thixotropy in emulsions is characterized by:

• Instant reversible viscosity change with shear
• Time-dependent recovery of viscosity after shear
• Permanent breakdown of emulsion structure on shear
• Viscosity increase with applied shear

Correct Answer: Time-dependent recovery of viscosity after shear

Q7. Which instrument is most commonly used for detailed emulsion rheological profiling?

• UV-Vis spectrophotometer
• Rotational rheometer
• Gas chromatograph
• Particle counter

Correct Answer: Rotational rheometer

Q8. In oscillatory rheology, G’ represents:

• Viscous modulus (loss modulus)
• Elastic modulus (storage modulus)
• Complex viscosity magnitude
• Yield stress value

Correct Answer: Elastic modulus (storage modulus)

Q9. An emulsion with G’ greater than G” in the linear viscoelastic region indicates:

• Dominant viscous behavior
• Dominant elastic (solid-like) behavior
• Complete phase separation
• Newtonian flow behavior

Correct Answer: Dominant elastic (solid-like) behavior

Q10. Increasing dispersed-phase volume fraction typically causes:

• Decrease in viscosity
• No change in rheology
• Increase in viscosity and possible yield stress
• Lowering of interfacial tension only

Correct Answer: Increase in viscosity and possible yield stress

Q11. Which factor most directly reduces droplet coalescence and affects rheology?

• Reducing temperature drastically
• Using appropriate surfactants to lower interfacial tension
• Increasing ambient light exposure
• Decreasing dispersed-phase volume fraction to zero

Correct Answer: Using appropriate surfactants to lower interfacial tension

Q12. Pseudoplastic behavior in emulsions means:

• Viscosity increases with shear (shear-thickening)
• Viscosity decreases with shear (shear-thinning)
• Viscosity is constant with shear
• Emulsion becomes gaseous on shear

Correct Answer: Viscosity decreases with shear (shear-thinning)

Q13. Which of the following is a non-Newtonian model that includes yield stress and shear-thinning?

• Newtonian model
• Herschel-Bulkley model
• Ideal Hookean model
• Michaelis-Menten model

Correct Answer: Herschel-Bulkley model

Q14. A flow curve plots which two variables?

• Viscosity vs. droplet size
• Shear stress vs. shear rate
• Temperature vs. time
• pH vs. conductivity

Correct Answer: Shear stress vs. shear rate

Q15. Hysteresis loop in a rheogram indicates:

• Instrument malfunction only
• Time-dependent structural breakdown and recovery (thixotropy)
• Perfectly reversible flow behavior
• Constant viscosity over cycles

Correct Answer: Time-dependent structural breakdown and recovery (thixotropy)

Q16. Which measurement detects viscoelastic behavior at small deformations?

• Steady shear viscosity test only
• Oscillatory (dynamic) rheometry
• Droplet size analysis by microscopy
• pH titration

Correct Answer: Oscillatory (dynamic) rheometry

Q17. Emulsions exhibiting dilatant behavior will:

• Show decreased viscosity with increasing shear
• Show increased viscosity with increasing shear
• Have constant viscosity
• Instantly phase separate under shear

Correct Answer: Show increased viscosity with increasing shear

Q18. Which formulation component acts as a rheology modifier by increasing continuous-phase viscosity?

• Low HLB surfactant only
• Polymers such as carbomers or xanthan gum
• Volatile oils
• Preservatives at low concentration

Correct Answer: Polymers such as carbomers or xanthan gum

Q19. The consistency index (K) in the power-law model represents:

• Shear rate at zero stress
• Apparent viscosity when shear rate equals one
• Droplet size distribution metric
• Interfacial tension unit

Correct Answer: Apparent viscosity when shear rate equals one

Q20. Emulsion stability against creaming is improved by:

• Increasing density difference between phases
• Increasing droplet size intentionally
• Reducing continuous-phase viscosity
• Reducing droplet size and increasing continuous-phase viscosity

Correct Answer: Reducing droplet size and increasing continuous-phase viscosity

Q21. Which rheological test is best for measuring yield stress?

• Simple dilution test
• Stress ramp or controlled stress rheometry
• Gas chromatography
• Microscopy

Correct Answer: Stress ramp or controlled stress rheometry

Q22. Ostwald ripening affects emulsions by:

• Droplets exchanging molecules leading to growth of larger droplets
• Immediate microbial spoilage
• Instant gelation of the continuous phase
• Reducing interfacial tension to zero

Correct Answer: Droplets exchanging molecules leading to growth of larger droplets

Q23. Which surfactant property strongly influences rheology and droplet stabilization?

• Color
• Hydrophilic-lipophilic balance (HLB)
• Melting point
• Electrical conductivity

Correct Answer: Hydrophilic-lipophilic balance (HLB)

Q24. Emulsions used for topical products often require which rheological characteristic?

• Extremely low viscosity for runoff
• High yield stress to prevent spreadability
• Balanced rheology: shear-thinning for easy spread and sufficient structure at rest
• Rigid solid-like behavior preventing application

Correct Answer: Balanced rheology: shear-thinning for easy spread and sufficient structure at rest

Q25. In a power-law fluid, the flow behavior index (n) less than 1 indicates:

• Newtonian behavior
• Shear-thinning behavior
• Shear-thickening behavior
• No flow at any stress

Correct Answer: Shear-thinning behavior

Q26. Which parameter is directly obtained from oscillatory frequency sweep?

• Droplet charge distribution
• G’ (storage modulus) and G” (loss modulus) as functions of frequency
• Interfacial tension values only
• pH stability range

Correct Answer: G’ (storage modulus) and G” (loss modulus) as functions of frequency

Q27. Emulsion rheology can influence drug release by:

• Altering the drug’s chemical identity
• Controlling diffusion through the continuous phase and structural network
• Only changing color and odor
• Removing drug from formulation entirely

Correct Answer: Controlling diffusion through the continuous phase and structural network

Q28. Which of the following reduces droplet flocculation and affects rheology?

• Adding electrolytes that screen repulsive charges, if uncontrolled
• Adding appropriate steric or electrostatic stabilizers
• Increasing temperature to boiling point
• Exposing the emulsion to UV light

Correct Answer: Adding appropriate steric or electrostatic stabilizers

Q29. The Cox-Merz rule relates:

• Oscillatory G’ to interfacial tension
• Complex viscosity from oscillatory tests to steady shear viscosity at equivalent frequencies/shear rates
• Droplet size to viscosity directly
• Yield stress to pH value

Correct Answer: Complex viscosity from oscillatory tests to steady shear viscosity at equivalent frequencies/shear rates

Q30. Which effect does temperature typically have on emulsion viscosity?

• Viscosity usually increases with increasing temperature
• Viscosity is independent of temperature
• Viscosity usually decreases with increasing temperature
• Temperature only affects color, not viscosity

Correct Answer: Viscosity usually decreases with increasing temperature

Q31. Which droplet characteristic most strongly affects rheology at high volume fractions?

• Droplet refractive index
• Droplet size distribution and polydispersity
• Color of the oil phase
• Presence of air bubbles only

Correct Answer: Droplet size distribution and polydispersity

Q32. Which rheological behavior is desirable in injectable emulsions to ensure syringeability?

• Extremely high yield stress
• Shear-thinning with low viscosity under high shear
• Dilatant behavior causing blockage
• Completely solid-like behavior

Correct Answer: Shear-thinning with low viscosity under high shear

Q33. Which of the following is NOT a direct cause of increased emulsion viscosity?

• Higher dispersed-phase concentration
• Larger droplet size with same volume fraction
• Inter-droplet attractive forces (flocculation)
• Higher continuous-phase polymer concentration

Correct Answer: Larger droplet size with same volume fraction

Q34. A sample showing a pronounced plateau in G’ across frequencies likely indicates:

• A purely viscous liquid
• A strong gel-like network or elastic structure
• Instrument noise only
• Immediate phase separation

Correct Answer: A strong gel-like network or elastic structure

Q35. For quality control of an emulsion batch, rheological tests are useful because they:

• Replace all microbiological testing
• Provide objective metrics for consistency, spreadability and stability
• Are cheaper than measuring pH
• Only measure color differences

Correct Answer: Provide objective metrics for consistency, spreadability and stability

Q36. Which phenomenon causes an increase in mean droplet size over time due to diffusion of dispersed phase molecules?

• Flocculation
• Ostwald ripening
• Creaming only
• Phase inversion instantly

Correct Answer: Ostwald ripening

Q37. Emulsions stabilized by polymers often show which rheological signature?

• Lower viscosity than surfactant-stabilized counterparts always
• Enhanced continuous-phase viscosity and potentially stronger gel-like behavior
• No measurable yield stress ever
• Instant solidification on standing

Correct Answer: Enhanced continuous-phase viscosity and potentially stronger gel-like behavior

Q38. Which sample preparation step is important before rheological measurement?

• Ensure sample is magnetized
• Equilibrate temperature and remove air bubbles
• Add excess solvent to change formulation
• Freeze and thaw repeatedly

Correct Answer: Equilibrate temperature and remove air bubbles

Q39. Which of the following best explains why small droplet size increases emulsion viscosity at constant volume fraction?

• Smaller droplets reduce surface area and interactions
• Smaller droplets increase total interfacial area leading to stronger interactions and hindered flow
• Droplet size has no effect on viscosity
• Smaller droplets always make emulsions Newtonian

Correct Answer: Smaller droplets increase total interfacial area leading to stronger interactions and hindered flow

Q40. The term “apparent viscosity” is used because:

• It is measured only at zero shear
• Non-Newtonian fluids have viscosity that depends on shear rate, so viscosity is an apparent value at a given condition
• It is unrelated to real viscosity measurements
• It only applies to gaseous systems

Correct Answer: Non-Newtonian fluids have viscosity that depends on shear rate, so viscosity is an apparent value at a given condition

Q41. Which rheological change would most likely indicate early coalescence in an emulsion?

• Gradual increase in viscosity with no other changes
• Sudden large increase in droplet size with reduced viscosity due to phase separation
• No change in any measured parameter
• Decrease in pH only

Correct Answer: Sudden large increase in droplet size with reduced viscosity due to phase separation

Q42. Emulsions with strong inter-droplet attractions often show:

• Lower elastic modulus and more fluid-like behavior
• Network formation, higher G’ and yield stress
• Instant vaporization
• Complete transparency always

Correct Answer: Network formation, higher G’ and yield stress

Q43. Which rheological parameter helps predict resistance to creaming under gravity?

• Electrical conductivity
• Continuous-phase viscosity and yield stress
• UV absorbance
• Colorimetric index

Correct Answer: Continuous-phase viscosity and yield stress

Q44. Emulsion inversion (oil-in-water to water-in-oil) can dramatically alter rheology because:

• It changes the dispersed and continuous phases, altering the microstructure and flow properties
• It only affects odor
• It always reduces viscosity to zero
• It makes the system sterile

Correct Answer: It changes the dispersed and continuous phases, altering the microstructure and flow properties

Q45. Which test differentiates between elastic and viscous dominant behavior at small strains?

• Steady shear rate sweep only
• Small-amplitude oscillatory shear (SAOS) test
• Droplet counting
• Thermal gravimetric analysis

Correct Answer: Small-amplitude oscillatory shear (SAOS) test

Q46. Surfactant concentration above critical micelle concentration (CMC) can affect emulsion rheology by:

• Having no effect at all
• Modifying interfacial properties and possibly increasing continuous-phase viscosity due to micelle formation
• Instant solidification of droplets
• Removing all oil from the emulsion

Correct Answer: Modifying interfacial properties and possibly increasing continuous-phase viscosity due to micelle formation

Q47. Which parameter is NOT typically obtained from a steady shear test?

• Shear stress versus shear rate
• Apparent viscosity at specific shear rates
• G’ and G” as functions of frequency
• Yield stress estimates using yield models

Correct Answer: G’ and G” as functions of frequency

Q48. How does electrolyte addition sometimes alter emulsion rheology?

• By altering surfactant charge screening, leading to flocculation and increased viscosity or phase separation
• By reducing droplet size to zero
• By making the continuous phase gaseous
• By always stabilizing the emulsion regardless of concentration

Correct Answer: By altering surfactant charge screening, leading to flocculation and increased viscosity or phase separation

Q49. Which outcome is expected when a polymeric thickener provides steric stabilization to an emulsion?

• Reduced continuous-phase viscosity and faster creaming
• Increased viscosity and reduced droplet aggregation through steric hindrance
• Immediate coalescence of droplets
• Increased volatility of the dispersed phase

Correct Answer: Increased viscosity and reduced droplet aggregation through steric hindrance

Q50. In formulation optimization, rheology is used to:

• Only determine color specifications
• Predict processability, stability, patient acceptability and drug release profiles
• Replace in vivo testing entirely
• Ensure the product is flammable

Correct Answer: Predict processability, stability, patient acceptability and drug release profiles

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com