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Questions and Answers
What does the term 'rheo' in rheology mean?
What does the term 'rheo' in rheology mean?
Rheology only studies the flow of gases.
Rheology only studies the flow of gases.
False
Name one way rheological properties can affect pharmaceutical products.
Name one way rheological properties can affect pharmaceutical products.
Drug absorption and bioavailability
Rheology is the study of the flow and deformation of matter under _____ .
Rheology is the study of the flow and deformation of matter under _____ .
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Match the following terms to their definitions:
Match the following terms to their definitions:
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What is the viscosity of glycerol at 20 °C?
What is the viscosity of glycerol at 20 °C?
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Relative viscosity has units of measurement.
Relative viscosity has units of measurement.
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Define kinematic viscosity.
Define kinematic viscosity.
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1 mPa·s is equivalent to ____ centipoise (cP).
1 mPa·s is equivalent to ____ centipoise (cP).
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Match the following fluids with their viscosities at 20 °C:
Match the following fluids with their viscosities at 20 °C:
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Study Notes
Viscosity and Rheology
- Viscosity is the resistance of a fluid to flow or movement.
- Higher viscosity means greater resistance to flow.
- Examples of high-viscosity liquids are castor oil, honey, and syrups.
- Viscosity affects various aspects of pharmaceutical products, including dosage form design, drug absorption, patient compliance, and the ease of use of formulations.
Introduction/Definitions
- Rheology is the study of flow and deformation of matter under stress.
- Rheology is a Greek term, coined by Eugene C. Bingham.
- "Rheo" means "to flow" and "logos" is from the Greek word "logia" which means "study of".
- Studying flow properties of liquids is critical to pharmacists.
- Flow behaviors of formulations like suspensions, simple liquids, gels, creams, and pastes can change when exposed to different stress conditions.
Importance of Studying Rheology
- Rheological properties affect dosage form creation, drug absorption, and patient acceptance.
- Patient compliance can be related to how easy and comfortable it is for patients to take the medication.
- The correct flow characteristics of formulations, such as suspensions and emulsions, ensure ease of dosing from containers.
- Pastes should easily squeeze out of tubes but should hold their shape without leakage.
Types of Flow Systems
- Newtonian fluids are simple fluids that follow Newton's law of viscosity (τ = ηγ).
- Viscosity (η) remains constant no matter how fast the fluid is flowing.
- A linear relationship exists between shear stress and shear rate for Newtonian fluids.
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Non-Newtonian fluids do not follow Newton's law of viscosity.
- Viscosity changes with shear rate.
- This includes Plastic flow, Pseudoplastic flow and Dilatant flow.
Plastic Flow
- Plastic flow is exhibited by concentrated suspensions, especially if the continuous phase has high viscosity or if the particles are flocculated.
- Flow only occurs when a certain shear stress (yield value) is exceeded.
- Yield value indicates the degree of flocculation in the suspension.
- The higher the degree of flocculation, the higher the yield value.
Pseudoplastic Flow
- Pseudoplastic materials exhibit decreased viscosity as shear rate increases.
- This is referred to as "shear thinning".
- Materials that exhibit this type of flow usually include aqueous dispersions of natural and chemically modified hydrocolloids or gums (like acacia, tragacanth, methylcellulose, carmellose, polyvinylpyrrolidone, and polyacrylic acid).
Dilatant Flow
- Dilatant flow is the opposite of pseudoplastic flow.
- Viscosity increases with increased shear rate.
- This is referred to as "shear thickening".
- This behavior is less common than plastic or pseudoplastic flow.
- This can occur in concentrated suspensions with a high concentration of small deflocculated particles.
Thixotropy
- Thixotropy is a time-dependent change in viscosity in certain non-Newtonian fluids, usually in shear-thinning systems.
- Thixotropic materials exhibit hysteresis loops in flow curves.
- The breakdown in structure occurs under high shear stress.
- Removal of the stress will restore the structure and viscosity.
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Description
Explore the essential concepts of viscosity and rheology, focusing on their impact on pharmaceutical products. Understand the significance of flow properties in dosage form design, drug absorption, and patient compliance. This quiz will reinforce your knowledge of how these principles affect the use of various formulations.
