Dilatant systems MCQs With Answer

Dilatant systems MCQs With Answer

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Introduction: Dilatant systems MCQs With Answer are essential study tools for B. Pharm students preparing for pharmaceutics and rheology exams. This collection focuses on dilatant (shear-thickening) behavior, viscosity changes under stress, measurement techniques such as viscometry and rheometry, formulation factors like particle size, concentration, and medium, and practical applications in suspensions and topical products. Questions emphasize mechanisms, experimental methods, interpretation of flow curves, and problem-solving in formulation design. Clear explanations and correct answers help reinforce concepts and improve exam performance. This targeted set will deepen understanding of non-Newtonian dilatant fluids and their pharmaceutical relevance. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the defining characteristic of a dilatant (shear-thickening) system?

  • Viscosity decreases with increasing shear rate
  • Viscosity remains constant with shear rate
  • Viscosity increases with increasing shear rate
  • Viscosity fluctuates randomly with shear rate

Correct Answer: Viscosity increases with increasing shear rate

Q2. Which mechanism is most commonly associated with shear thickening in concentrated suspensions?

  • Formation of permanent chemical bonds between particles
  • Hydrocluster formation and particle jamming under shear
  • Polymer chain disentanglement
  • Decrease in particle concentration due to shear

Correct Answer: Hydrocluster formation and particle jamming under shear

Q3. At what approximate particle volume fraction do many suspensions begin to show dilatant behavior?

  • Less than 10%
  • Around 20–30%
  • Above a critical fraction typically >40%–50%
  • Only at 100% packing

Correct Answer: Above a critical fraction typically >40%–50%

Q4. Which experimental instrument is most appropriate for detailed characterization of shear-thickening behavior?

  • High-performance liquid chromatograph (HPLC)
  • Cone-and-plate or parallel-plate rheometer
  • UV-Vis spectrophotometer
  • Analytical balance

Correct Answer: Cone-and-plate or parallel-plate rheometer

Q5. How does particle size distribution influence dilatancy in suspensions?

  • Monodisperse particles always prevent shear thickening
  • Broad distributions can reduce jamming and delay dilatancy
  • Smaller mean particle size always eliminates shear thickening
  • Size distribution has no effect on rheology

Correct Answer: Broad distributions can reduce jamming and delay dilatancy

Q6. Which of the following best distinguishes dilatancy from thixotropy?

  • Dilatancy is time-dependent viscosity recovery, thixotropy is shear-rate dependent thickening
  • Dilatancy is shear-rate dependent thickening, thixotropy is time-dependent viscosity decrease and recovery
  • Both are identical phenomena
  • Thixotropy leads to permanent solidification on shear

Correct Answer: Dilatancy is shear-rate dependent thickening, thixotropy is time-dependent viscosity decrease and recovery

Q7. Which pharmaceutical formulation problem can be caused by unexpected dilatant behavior?

  • Improved syringeability of injected suspensions
  • Decreased sedimentation rate
  • Difficulty in pumping, mixing, and spraying due to sudden viscosity increase
  • Enhanced dissolution of active drug

Correct Answer: Difficulty in pumping, mixing, and spraying due to sudden viscosity increase

Q8. How does adding a high-molecular-weight polymer that adsorbs on particle surfaces typically affect dilatant suspensions?

  • Always increases shear thickening by bridging particles
  • May sterically stabilize particles and suppress shear thickening
  • Has no effect on interparticle interactions
  • Instantly converts system to Newtonian fluid

Correct Answer: May sterically stabilize particles and suppress shear thickening

Q9. In a flow curve (viscosity vs shear rate) for a dilatant fluid, what is typically observed?

  • Viscosity decreases monotonically with increasing shear rate
  • Viscosity increases at higher shear rates after an initial plateau
  • Viscosity is zero at all shear rates
  • Viscosity oscillates sinusoidally with shear rate

Correct Answer: Viscosity increases at higher shear rates after an initial plateau

Q10. Which of the following is a classic everyday example of a dilatant material?

  • Honey
  • Oobleck (cornstarch in water)
  • Sugar syrup
  • Olive oil

Correct Answer: Oobleck (cornstarch in water)

Q11. How does increasing temperature generally affect shear-thickening behavior in colloidal suspensions?

  • Always increases dilatancy due to thermal expansion
  • Often reduces solvent viscosity and Brownian motion effects, which can shift onset of thickening
  • Has no effect on rheological properties
  • Automatically turns system into a Newtonian liquid

Correct Answer: Often reduces solvent viscosity and Brownian motion effects, which can shift onset of thickening

Q12. Which interparticle force change would most likely promote shear thickening in charged colloids?

  • Increasing electrostatic repulsion
  • Strong steric hindrance from adsorbed polymers
  • Reduction of repulsive forces (e.g., by adding salt) promoting closer contact under shear
  • Introduction of strong covalent bonding in the dispersion medium

Correct Answer: Reduction of repulsive forces (e.g., by adding salt) promoting closer contact under shear

Q13. What role does solvent viscosity play in observing dilatant behavior?

  • Solvent viscosity is irrelevant to suspension rheology
  • Higher solvent viscosity can mask or delay observable shear thickening by damping particle collisions
  • Lower solvent viscosity always eliminates dilatancy
  • Solvent viscosity converts suspensions to emulsions

Correct Answer: Higher solvent viscosity can mask or delay observable shear thickening by damping particle collisions

Q14. Which rheological parameter measured in oscillatory tests can indicate microstructure changes related to dilatancy?

  • pH
  • Storage modulus (G’) and loss modulus (G”)
  • Conductivity
  • Optical density

Correct Answer: Storage modulus (G’) and loss modulus (G”)

Q15. When preparing a concentrated suspension for a topical product, which strategy can help minimize dilatant behavior?

  • Increase particle concentration above the jamming point
  • Use monodisperse, rigid particles with no surface treatment
  • Introduce appropriate dispersants or steric stabilizers to reduce particle friction
  • Eliminate all lubricant additives

Correct Answer: Introduce appropriate dispersants or steric stabilizers to reduce particle friction

Q16. Which descriptor best fits dilatant flow in the context of non-Newtonian fluids?

  • Pseudoplastic
  • Dilatant is another term for Newtonian
  • Shear-thickening non-Newtonian
  • Bingham plastic only

Correct Answer: Shear-thickening non-Newtonian

Q17. In syringeability testing, why are dilatant suspensions problematic?

  • They dissolve too quickly in the syringe
  • They may exhibit sudden resistance at higher plunger speeds due to shear thickening
  • They become Newtonian on compression
  • Syringes catalyze polymerization, causing precipitation

Correct Answer: They may exhibit sudden resistance at higher plunger speeds due to shear thickening

Q18. Which formulation parameter is LEAST likely to influence dilatant behavior?

  • Particle surface chemistry
  • Particle concentration
  • Drug molecular weight when fully dissolved in solvent
  • Particle shape and roughness

Correct Answer: Drug molecular weight when fully dissolved in solvent

Q19. How does particle shape affect dilatancy?

  • Spherical smooth particles always maximize shear thickening
  • Irregular or rough particles can increase friction and promote dilatancy
  • Particle shape has no role if concentration is low
  • Only hollow particles can show shear thickening

Correct Answer: Irregular or rough particles can increase friction and promote dilatancy

Q20. Which measurement indicates the onset of shear thickening in a controlled shear rate experiment?

  • A sudden drop in normal force
  • An abrupt increase in measured viscosity or stress with small shear rate increment
  • Complete disappearance of torque reading
  • A linear decrease in stress with increasing shear rate

Correct Answer: An abrupt increase in measured viscosity or stress with small shear rate increment

Q21. In terms of interparticle lubrication, what happens during shear thickening?

  • Lubrication layers always thicken and prevent contact
  • Hydrodynamic lubrication can break down, leading to direct frictional contacts and jamming
  • Particles dissolve into the medium
  • Hydrodynamic interactions are completely negligible

Correct Answer: Hydrodynamic lubrication can break down, leading to direct frictional contacts and jamming

Q22. Which additive is most likely to reduce dilatant behavior in a pharmaceutical suspension?

  • Electrolytes that screen repulsion and promote aggregation
  • High concentration of small hard particles
  • Non-adsorbing polymers that cause depletion attraction
  • Surface-active steric dispersants that create a soft repulsive layer

Correct Answer: Surface-active steric dispersants that create a soft repulsive layer

Q23. How does shear thickening affect sprayability of suspensions in oral nasal or topical sprays?

  • Improves spray formation by lowering viscosity at nozzle
  • Can clog nozzles or require higher pressure due to increased viscosity at high shear
  • Has no impact since spray uses only airflow
  • Automatically converts spray to foam

Correct Answer: Can clog nozzles or require higher pressure due to increased viscosity at high shear

Q24. Which type of particles are most prone to exhibit shear-thickening when well-dispersed at high volume fraction?

  • Low-concentration soluble molecules
  • Concentrated suspensions of rigid, nondeformable colloidal particles
  • Gas bubbles in liquid
  • Highly elastic polymer networks at low solids

Correct Answer: Concentrated suspensions of rigid, nondeformable colloidal particles

Q25. The term “hydrocluster” in the context of dilatant systems refers to:

  • A group of solvent molecules forming a micelle
  • A transient, shear-induced aggregation of particles that increases local viscosity
  • A permanent covalent polymer cluster
  • An air bubble cluster in foams

Correct Answer: A transient, shear-induced aggregation of particles that increases local viscosity

Q26. Which analysis helps determine whether a concentrated suspension will display dilatant behavior due to steric or electrostatic stabilization?

  • X-ray crystallography
  • Zeta potential and adsorption isotherm studies
  • Melting point determination
  • Gas chromatography

Correct Answer: Zeta potential and adsorption isotherm studies

Q27. What is the effect of increasing ionic strength in a charged colloidal suspension on dilatancy?

  • It always decreases particle collisions and prevents thickening
  • Screening of charges can reduce electrostatic repulsion and increase propensity for shear thickening
  • Ionic strength has no effect on colloids
  • It converts suspension into a solution

Correct Answer: Screening of charges can reduce electrostatic repulsion and increase propensity for shear thickening

Q28. Which experimental observation suggests a transition from lubricated to frictional contacts among particles?

  • Decrease in yield stress
  • Appearance of a steep upward slope in stress vs shear rate and large increase in normal stress
  • Decrease in normal stress with shear
  • Complete elimination of viscosity

Correct Answer: Appearance of a steep upward slope in stress vs shear rate and large increase in normal stress

Q29. For quality control of a dilatant topical suspension, which parameter is most critical to monitor?

  • Particle color only
  • Shear-rate dependent viscosity and rheological profile
  • Boiling point of solvent
  • Flame point

Correct Answer: Shear-rate dependent viscosity and rheological profile

Q30. What is a practical laboratory test to quickly screen for shear thickening behavior?

  • Measure pH at rest
  • Apply increasing shear rates in a simple viscometer and look for viscosity rise at high shear
  • Freeze the sample and check texture
  • Measure UV absorption

Correct Answer: Apply increasing shear rates in a simple viscometer and look for viscosity rise at high shear

Q31. How does surface roughness of particles influence dilatant behavior?

  • Smoother surfaces always increase dilatancy
  • Rougher surfaces increase frictional contacts and favor shear thickening
  • Surface roughness only affects optical properties
  • Roughness eliminates all interparticle forces

Correct Answer: Rougher surfaces increase frictional contacts and favor shear thickening

Q32. Which of the following statements about yield stress and dilatancy is correct?

  • Dilatant fluids cannot have yield stress
  • Some concentrated suspensions can exhibit both yield stress at low shear and shear thickening at high shear
  • Yield stress always eliminates any non-Newtonian behavior
  • Dilatancy only occurs below yield stress

Correct Answer: Some concentrated suspensions can exhibit both yield stress at low shear and shear thickening at high shear

Q33. Why is control of pH important in colloidal suspensions prone to shear thickening?

  • pH changes change color but not interactions
  • pH influences surface charge and thus interparticle electrostatic repulsion affecting dilatancy
  • pH only affects microbial growth, not rheology
  • pH converts solids to gases

Correct Answer: pH influences surface charge and thus interparticle electrostatic repulsion affecting dilatancy

Q34. In formulating an injectable suspension, what target should be avoided to reduce risk of shear thickening during injection?

  • Very low particle concentration
  • High volume fraction near jamming
  • Use of lubricating excipients
  • Uniform particle size distribution

Correct Answer: High volume fraction near jamming

Q35. How can microscopy complement rheological studies of dilatant systems?

  • Microscopy provides direct evidence of shear-induced microstructure changes like clustering and contacts
  • Microscopy replaces the need for rheometry entirely
  • Microscopy measures viscosity directly
  • Microscopy detects chemical degradation only

Correct Answer: Microscopy provides direct evidence of shear-induced microstructure changes like clustering and contacts

Q36. Which colloidal interaction modification would MOST LIKELY suppress shear thickening in a nonpolar medium?

  • Reduce steric stabilizers to allow particle contact
  • Add or increase steric polymer layers on particle surfaces
  • Increase ionic strength
  • Add abrasive particles

Correct Answer: Add or increase steric polymer layers on particle surfaces

Q37. Which descriptor applies to a fluid that shows a rapid reversible increase in viscosity with shear but returns to initial viscosity quickly on rest?

  • Poorly designed Newtonian
  • Dilatant behavior with reversible microstructure
  • Irreversible gelation
  • Dry powder behavior

Correct Answer: Dilatant behavior with reversible microstructure

Q38. Which property of excipients is important to consider when managing dilatant responses in pharmaceutical suspensions?

  • Melting point alone
  • Ability to adsorb on particle surfaces and provide steric/electrostatic stabilization
  • Only color and fragrance
  • Boiling point alone

Correct Answer: Ability to adsorb on particle surfaces and provide steric/electrostatic stabilization

Q39. How does the rate of applied shear (shear rate) relate to observation of shear thickening?

  • Shear thickening is observed at low shear rates only
  • There is often a critical shear rate above which viscosity increases sharply
  • Shear rate has no effect on non-Newtonian behavior
  • Viscosity decreases at all shear rates beyond the critical point

Correct Answer: There is often a critical shear rate above which viscosity increases sharply

Q40. Which industrial practice can inadvertently induce dilatancy during manufacturing of suspensions?

  • Gentle slow stirring only
  • High-speed mixing or pumping that raises shear rates locally
  • Keeping the system at rest at all times
  • Using too many temperature sensors

Correct Answer: High-speed mixing or pumping that raises shear rates locally

Q41. Which mathematical model is commonly used to describe non-Newtonian shear-thinning behavior but is NOT appropriate for dilatant systems without modification?

  • Power-law (Ostwald-de Waele) model in its simple shear-thinning form
  • Models incorporating shear-thickening terms
  • Frictional contact models for dilatancy
  • Microstructural hydrocluster models

Correct Answer: Power-law (Ostwald-de Waele) model in its simple shear-thinning form

Q42. In dispersions exhibiting dilatancy, what is a typical behavior of normal stress differences during shear?

  • Normal stresses remain zero
  • Large positive normal stresses may develop as particles push against each other
  • Normal stresses always become negative
  • Normal stresses fluctuate randomly with no correlation to shear

Correct Answer: Large positive normal stresses may develop as particles push against each other

Q43. What safety concern arises from dilatant behavior in slurry handling during pharmaceutical production?

  • Reduced cleaning requirements
  • Sudden pressure spikes in pumps or pipes, potentially causing equipment failure
  • Lower viscosity makes spills less likely
  • No impact on equipment safety

Correct Answer: Sudden pressure spikes in pumps or pipes, potentially causing equipment failure

Q44. How can rheological modifiers be screened to reduce dilatancy without compromising product performance?

  • Only by guessing and checking in production scale
  • By small-scale rheometry combined with stability and sensory testing to assess viscosity at relevant shear rates
  • By measuring only density changes
  • By relying solely on supplier claims

Correct Answer: By small-scale rheometry combined with stability and sensory testing to assess viscosity at relevant shear rates

Q45. Which of the following best explains why hydrodynamic interactions are important in shear thickening?

  • Hydrodynamic forces are negligible compared to gravity
  • Fluid-mediated forces control particle approach and can enhance transient clustering under shear
  • Hydrodynamics only apply to gas phases
  • Hydrodynamic interactions dissolve particles

Correct Answer: Fluid-mediated forces control particle approach and can enhance transient clustering under shear

Q46. Which experimental observation would suggest suppression of shear thickening after adding a polymeric dispersant?

  • Increase in turbidity only
  • Shift of onset of viscosity increase to higher shear rates or elimination of steep viscosity rise
  • Immediate phase separation
  • Complete solidification at rest

Correct Answer: Shift of onset of viscosity increase to higher shear rates or elimination of steep viscosity rise

Q47. What is the pharmaceutical significance of understanding dilatant behavior in oral suspensions?

  • It is only academic with no real-world impact
  • It affects dosing accuracy, syringeability, mouthfeel, and manufacturing processes
  • It ensures active drug converts to gas
  • It prevents dissolution entirely

Correct Answer: It affects dosing accuracy, syringeability, mouthfeel, and manufacturing processes

Q48. Which strategy can be used to model dilatant flow in a formulation simulation?

  • Ignore particle interactions and use ideal gas law
  • Incorporate microstructural and frictional contact models calibrated with rheometry data
  • Assume constant viscosity equal to water
  • Use only thermal conductivity data

Correct Answer: Incorporate microstructural and frictional contact models calibrated with rheometry data

Q49. During accelerated stability testing, how might dilatant suspensions behave differently from simple Newtonian solutions?

  • They will always become clear solutions
  • They may show changes in flow behavior due to particle aggregation, binder loss, or changes in surface chemistry
  • They are unaffected by storage conditions
  • They instantly convert to gases

Correct Answer: They may show changes in flow behavior due to particle aggregation, binder loss, or changes in surface chemistry

Q50. Which combination of formulation choices is most likely to minimize shear thickening while maintaining high solids loading?

  • High solids loading with no stabilizer and rough particles
  • Moderate solids loading, use of steric stabilizers, and broad particle size distribution to improve packing
  • Maximize ionic strength and remove polymeric excipients
  • Use only very large irregular particles at high concentration

Correct Answer: Moderate solids loading, use of steric stabilizers, and broad particle size distribution to improve packing

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