Thixotropy MCQs With Answer

Thixotropy MCQs With Answer are essential study material for B.Pharm students studying pharmaceutics and rheology. This introduction covers thixotropy definition, mechanisms, measurement techniques, and pharmaceutical relevance — highlighting keywords such as thixotropy, rheology, viscosity, time-dependent shear thinning, gels, suspensions, and rheometers. Understanding thixotropic behavior helps formulators predict spreadability, stability, and syringeability of topical and parenteral preparations. Practical topics include hysteresis loops, thixotropic index, recovery time, and common excipients (e.g., carbomers, xanthan gum) that exhibit thixotropy. The questions below are designed to reinforce core concepts, test analytical skills, and prepare you for exams and formulation design. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the best definition of thixotropy in pharmaceutical rheology?

• A reversible decrease in viscosity over time under constant shear and recovery when shear is removed
• An irreversible increase in viscosity with increasing shear rate
• A time-independent shear-thinning behavior
• A material that becomes more elastic with shear

Correct Answer: A reversible decrease in viscosity over time under constant shear and recovery when shear is removed

Q2. Which rheological test is most commonly used to demonstrate thixotropy?

• Hysteresis loop by increasing and decreasing shear rate
• Steady-state creep only
• Constant temperature differential scanning
• Static contact angle measurement

Correct Answer: Hysteresis loop by increasing and decreasing shear rate

Q3. Which excipient is well-known for imparting thixotropic behavior to topical gels?

• Carbomer
• Sodium chloride
• Polyethylene glycol 400
• Propylene glycol

Correct Answer: Carbomer

Q4. How does thixotropy differ from pseudoplasticity?

• Thixotropy is time-dependent viscosity decrease; pseudoplasticity is time-independent shear-thinning
• They are the same phenomena described differently
• Pseudoplasticity is time-dependent; thixotropy is rate-dependent only
• Thixotropy indicates viscosity increase with time at constant shear

Correct Answer: Thixotropy is time-dependent viscosity decrease; pseudoplasticity is time-independent shear-thinning

Q5. The area of the hysteresis loop in a shear rate sweep is used to quantify:

• Thixotropic behavior magnitude
• Solubility of drug in vehicle
• Evaporation rate of solvent
• pH stability range

Correct Answer: Thixotropic behavior magnitude

Q6. Which parameter indicates the speed of structural recovery after shear in a thixotropic system?

• Recovery time
• pKa of the drug
• Glass transition temperature
• Particle size distribution

Correct Answer: Recovery time

Q7. Which polymeric system commonly shows thixotropy due to reversible network formation?

• Xanthan gum
• Sodium lauryl sulfate micelles only
• Simple alcohol solutions
• Sucrose syrup

Correct Answer: Xanthan gum

Q8. In a typical thixotropy test, what happens to viscosity when shear is applied for a period?

• Viscosity decreases with time under constant shear
• Viscosity increases irreversibly
• Viscosity remains constant regardless of shear
• Viscosity changes unpredictably without relation to shear

Correct Answer: Viscosity decreases with time under constant shear

Q9. Which instrument is primarily used to measure thixotropic properties of semisolids?

• Rotational rheometer
• UV-visible spectrophotometer
• Gas chromatograph
• Polarimeter

Correct Answer: Rotational rheometer

Q10. Thixotropic index is often defined as:

• The ratio or difference between viscosities (or shear stresses) during up and down shear sweeps
• The pH at which viscosity is highest
• The molecular weight of the gelling agent
• The temperature coefficient of viscosity

Correct Answer: The ratio or difference between viscosities (or shear stresses) during up and down shear sweeps

Q11. Which pharmaceutical property benefits from thixotropy in topical creams?

• Improved spreadability and residence time on skin
• Increased systemic absorption irrespective of formulation
• Complete resistance to microbial growth
• Higher osmolarity

Correct Answer: Improved spreadability and residence time on skin

Q12. Thixotropy in suspensions is often due to:

• Reversible flocculation forming a network structure
• Complete dissolution of particles
• Permanent chemical cross-linking
• Rapid sedimentation unaffected by shear

Correct Answer: Reversible flocculation forming a network structure

Q13. Which of the following best describes rheopexy (the opposite of thixotropy)?

• Viscosity increases with time under constant shear
• Viscosity decreases immediately and permanently
• Viscosity is independent of time and shear
• System shows no change after shear removal

Correct Answer: Viscosity increases with time under constant shear

Q14. During formulation, adding electrolytes to a polyelectrolyte gel may:

• Alter thixotropic behavior by changing interparticle interactions
• Have no effect on rheology
• Always convert gel into a Newtonian liquid
• Make viscosity measurement impossible

Correct Answer: Alter thixotropic behavior by changing interparticle interactions

Q15. A large hysteresis loop area indicates:

• Greater thixotropy (more structural breakdown and slower recovery)
• No thixotropy present
• Faster structural rebuild after shear
• Complete Newtonian behavior

Correct Answer: Greater thixotropy (more structural breakdown and slower recovery)

Q16. Which test sequence most clearly demonstrates thixotropy?

• Apply high shear, measure viscosity decrease, stop shear and measure viscosity recovery over time
• Measure viscosity only at a single shear rate once
• Heat sample above melting point and measure density
• Measure pH change under stirring

Correct Answer: Apply high shear, measure viscosity decrease, stop shear and measure viscosity recovery over time

Q17. In oscillatory rheology, thixotropic recovery is often assessed by monitoring:

• Recovery of storage modulus (G’) and loss modulus (G”) after shear
• Only the complex refractive index
• Heat flow during gelation
• Particle zeta potential exclusively

Correct Answer: Recovery of storage modulus (G’) and loss modulus (G”) after shear

Q18. Which factor typically accelerates structural breakdown in a thixotropic system?

• Increasing shear rate
• Lowering solvent polarity only
• Decreasing temperature to absolute zero
• Eliminating any mechanical stress

Correct Answer: Increasing shear rate

Q19. Thixotropic behavior is most critical to consider for which dosage form?

• Topical gels and creams
• Immediate-release tablets that disintegrate in water
• Dry powder inhalers with no liquid vehicle
• Hard gelatin capsules only

Correct Answer: Topical gels and creams

Q20. Which microstructural phenomenon underlies thixotropy in many colloidal gels?

• Breakdown and reversible re-formation of particle-particle networks
• Complete covalent crosslinking forming permanent networks
• Instant dissolution of polymer chains into monomers
• Formation of irreversible crystalline precipitates

Correct Answer: Breakdown and reversible re-formation of particle-particle networks

Q21. When measuring thixotropy, why is controlling temperature important?

• Temperature affects viscosity and kinetic rates of structural recovery
• Temperature has no effect on thixotropic properties
• Only pH affects thixotropy, not temperature
• Temperature only affects color, not rheology

Correct Answer: Temperature affects viscosity and kinetic rates of structural recovery

Q22. Which of the following is a practical advantage of thixotropic eye drops? (hypothetical)

• Low viscosity during blinking and high viscosity at rest to prolong contact time
• Permanent increase in viscosity causing poor spreading
• Complete precipitation of drug on the cornea
• Immediate elimination from the eye after administration

Correct Answer: Low viscosity during blinking and high viscosity at rest to prolong contact time

Q23. Which mathematical model specifically accounts for time-dependent viscosity change?*

• Structural kinetics models (thixotropic models) incorporating breakdown/rebuild kinetics
• Arrhenius equation for diffusion
• Beer-Lambert law
• Henderson-Hasselbalch equation

Correct Answer: Structural kinetics models (thixotropic models) incorporating breakdown/rebuild kinetics

Q24. In practice, to increase thixotropy of a formulation, a formulator may:

• Add a small amount of a network-forming thickener like xanthan or fumed silica
• Remove all polymers and use only low molecular weight solvents
• Add volatile organic solvent to evaporate quickly
• Increase ionic strength to fully dissolve polymer chains

Correct Answer: Add a small amount of a network-forming thickener like xanthan or fumed silica

Q25. Which statement about Newtonian fluids is correct compared to thixotropic fluids?

• Newtonian fluids have constant viscosity independent of shear rate and time
• Newtonian fluids always show time-dependent viscosity decrease
• Newtonian fluids have large hysteresis loops
• Newtonian behavior always indicates thixotropy

Correct Answer: Newtonian fluids have constant viscosity independent of shear rate and time

Q26. Which rheological parameter would you monitor to assess flow recovery after shear?

• Viscosity or modulus recovery versus time
• Melting point depression
• Optical rotation changes
• Conductivity at infinite frequency

Correct Answer: Viscosity or modulus recovery versus time

Q27. A thixotropic gel used in syringeable formulations should ideally show:

• Low viscosity under high shear (easy injection) and fast recovery at rest
• Very high viscosity under shear making injection impossible
• No change in viscosity under shear
• Complete phase separation on shearing

Correct Answer: Low viscosity under high shear (easy injection) and fast recovery at rest

Q28. Which of the following contributes least to thixotropic behavior?

• Non-interacting small solvent molecules
• Particle flocculation
• Polymer entanglement and weak cross-links
• Physical gel networks

Correct Answer: Non-interacting small solvent molecules

Q29. During an increasing-decreasing shear rate test, if the down-curve lies below the up-curve, this indicates:

• Thixotropy (time-dependent structural breakdown)
• Rheopexy
• Newtonian behavior
• Shear thickening

Correct Answer: Thixotropy (time-dependent structural breakdown)

Q30. Which excipient combination might reduce thixotropy by screening electrostatic interactions?

• Addition of high concentration of electrolytes
• Adding more network-forming polymer
• Increasing pH to extreme limits without ionic change
• Decreasing formulation temperature only

Correct Answer: Addition of high concentration of electrolytes

Q31. Thixotropic index is useful in quality control to:

• Compare batch-to-batch rheological consistency
• Measure microbial contamination directly
• Determine API potency chemically
• Assess color stability exclusively

Correct Answer: Compare batch-to-batch rheological consistency

Q32. Which observation suggests that a gel is truly thixotropic rather than simply shear-thinning?

• Viscosity recovers partially or fully over time after shear is removed
• Viscosity is low at high shear but instantly reverts to initial value on stopping
• Viscosity does not change with prolonged shear
• Gel dissolves chemically on shearing

Correct Answer: Viscosity recovers partially or fully over time after shear is removed

Q33. In designing a suspension, maintaining thixotropy can help prevent:

• Rapid sedimentation and caking by providing a structured network at rest
• All dissolution of the active ingredient
• Increase in chemical stability of API inherently
• Excessive foaming during storage

Correct Answer: Rapid sedimentation and caking by providing a structured network at rest

Q34. Which polymer would you expect to show fast recovery after shear due to reversible non-covalent bonds?

• Associative polymers with weak physical crosslinks
• Irreversibly chemically crosslinked gels
• Small molecule salts only
• Non-associating low molecular weight alcohols

Correct Answer: Associative polymers with weak physical crosslinks

Q35. Which variable is least likely to affect thixotropic behavior?

• Colorant chemical structure (assuming inert dye)
• Polymer concentration
• Shear history and duration
• Temperature

Correct Answer: Colorant chemical structure (assuming inert dye)

Q36. What does a time-dependent drop in shear stress at constant shear rate indicate?

• Thixotropic breakdown of internal structure
• Rheopexy-induced strengthening
• Newtonian behavior
• Instrument malfunction only

Correct Answer: Thixotropic breakdown of internal structure

Q37. Which formulation factor will most likely increase thixotropy in an oil-in-water cream?

• Higher concentration of hydrophobically modified carbomer
• Removal of emulsifier completely
• Replacing water with ethanol only
• Decreasing oil phase volume to zero

Correct Answer: Higher concentration of hydrophobically modified carbomer

Q38. In the context of thixotropy, what role do weak physical bonds (hydrogen bonds, van der Waals) play?

• Allow reversible network formation and recovery after shear
• Create permanent chemical crosslinks that never reform
• Eliminate any viscoelastic response
• Prevent any particle-particle interactions

Correct Answer: Allow reversible network formation and recovery after shear

Q39. Which oscillatory test parameter can be used to detect structural breakdown during shear?

• Drop in storage modulus (G’) with applied strain or stress
• Increase in pH during oscillation
• Change in boiling point
• Optical density at 700 nm

Correct Answer: Drop in storage modulus (G’) with applied strain or stress

Q40. For a thixotropic cream intended for skin application, an ideal behavior is:

• Shear-thin on rubbing and rapidly recover structure to avoid run-off
• Remain rigid when rubbed to prevent spread
• Become permanently fluid after first use
• Show no response to shear at any time

Correct Answer: Shear-thin on rubbing and rapidly recover structure to avoid run-off

Q41. Which property is most directly measured by a rotational rheometer during thixotropy testing?

• Shear stress and viscosity as functions of shear rate and time
• pH changes with stirring
• UV absorbance of the formulation
• Thermal conductivity

Correct Answer: Shear stress and viscosity as functions of shear rate and time

Q42. A formulation shows little viscosity recovery even after long rest—this suggests:

• Irreversible structural damage or very slow rebuild kinetics
• Excellent thixotropic recovery suitable for application
• Immediate conversion to Newtonian behavior with fast recovery
• That the sample is a perfect elastic solid

Correct Answer: Irreversible structural damage or very slow rebuild kinetics

Q43. Which of the following is a sign that rheological measurements were not properly performed for thixotropy assessment?

• Lack of controlled shear history and temperature during measurements
• Using a calibrated rheometer and documented protocol
• Running replicate tests and averaging results
• Recording both up and down shear curves

Correct Answer: Lack of controlled shear history and temperature during measurements

Q44. How does particle size affect thixotropy in suspensions?

• Smaller particles with high surface area may form stronger networks and increase thixotropy
• Particle size has no influence on structural interactions
• Larger particles always increase thixotropy more than smaller ones
• Only particle color affects network formation

Correct Answer: Smaller particles with high surface area may form stronger networks and increase thixotropy

Q45. In formulation troubleshooting, if a product shows excessive run-off, a formulator may:

• Increase thixotropic agents to raise low-shear viscosity and enable recovery
• Remove all thickeners to lower viscosity further
• Convert to a dry powder without excipients
• Replace water with volatile solvent to evaporate instantly

Correct Answer: Increase thixotropic agents to raise low-shear viscosity and enable recovery

Q46. Which recovery pattern indicates strong thixotropic network rebuild?

• Rapid increase in viscosity or modulus reaching close to original value
• No change in viscosity after stopping shear
• Complete dissolution into monomers
• Immediate crystallization upon shear removal

Correct Answer: Rapid increase in viscosity or modulus reaching close to original value

Q47. Why is understanding thixotropy important for parenteral suspensions?

• To ensure ease of syringeability and prevent clogging while maintaining suspension stability at rest
• Because parenteral suspensions never experience shear
• It is irrelevant; only chemical sterility matters
• To promote permanent aggregation before injection

Correct Answer: To ensure ease of syringeability and prevent clogging while maintaining suspension stability at rest

Q48. Which additive might reduce thixotropic behavior by breaking polymer associations?

• Non-ionic surfactant at high concentration
• Additional gelling agent that forms networks
• Fumed silica that strengthens network
• Associative thickener that enhances interactions

Correct Answer: Non-ionic surfactant at high concentration

Q49. In a thixotropy experiment, a material shows immediate viscosity recovery on stopping shear; this suggests:

• Predominantly elastic behavior with little structural breakage
• Complete irreversible breakdown of structure
• Strong evidence of rheopexy
• That the sample is a perfect liquid with no structure

Correct Answer: Predominantly elastic behavior with little structural breakage

Q50. Which statement best summarizes the pharmaceutical importance of thixotropy?

• It allows formulations to flow under stress (application, injection) yet remain stable and retained at rest, improving usability and performance
• It makes formulations impossible to manufacture
• It always causes chemical degradation of APIs
• It is an academic concept with no practical relevance

Correct Answer: It allows formulations to flow under stress (application, injection) yet remain stable and retained at rest, improving usability and performance

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