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Questions and Answers
What is the term defined as the reciprocal of viscosity?
What is the term defined as the reciprocal of viscosity?
What is the unit of kinematic viscosity?
What is the unit of kinematic viscosity?
What is the viscosity of water at 25°C?
What is the viscosity of water at 25°C?
What happens to the viscosity of a liquid as temperature is raised?
What happens to the viscosity of a liquid as temperature is raised?
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What is the equation that expresses the dependence of the viscosity of a liquid on temperature?
What is the equation that expresses the dependence of the viscosity of a liquid on temperature?
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What is the characteristic of the majority of fluid pharmaceutical products?
What is the characteristic of the majority of fluid pharmaceutical products?
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What is the literal meaning of the term 'rheology'?
What is the literal meaning of the term 'rheology'?
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What is the primary characteristic of Newtonian systems?
What is the primary characteristic of Newtonian systems?
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Why is rheology significant in pharmaceutical products?
Why is rheology significant in pharmaceutical products?
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What type of flow does a dilatant system exhibit?
What type of flow does a dilatant system exhibit?
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What is the purpose of determining rheologic properties in pharmaceutical products?
What is the purpose of determining rheologic properties in pharmaceutical products?
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What is the significance of analytic methods of rheology in pharmaceutical product development?
What is the significance of analytic methods of rheology in pharmaceutical product development?
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What is the hysteresis loop in a rheogram?
What is the hysteresis loop in a rheogram?
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Why is it important to consider the time of shear, rate of shear, and degree of structure in the sample when measuring thixotropy?
Why is it important to consider the time of shear, rate of shear, and degree of structure in the sample when measuring thixotropy?
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What is the thixotropic coefficient B, as mentioned in the text?
What is the thixotropic coefficient B, as mentioned in the text?
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What is the purpose of calculating the plastic viscosities U1 and U2 in the equation for the thixotropic coefficient B?
What is the purpose of calculating the plastic viscosities U1 and U2 in the equation for the thixotropic coefficient B?
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What is the main difference between the two approaches to estimate the degree of thixotropy in plastic systems?
What is the main difference between the two approaches to estimate the degree of thixotropy in plastic systems?
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What is the significance of the area of the hysteresis loop in measuring thixotropy?
What is the significance of the area of the hysteresis loop in measuring thixotropy?
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What is the primary difference between rheopexy and antithixotropy?
What is the primary difference between rheopexy and antithixotropy?
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Why are single-point instruments insufficient for characterizing non-Newtonian systems?
Why are single-point instruments insufficient for characterizing non-Newtonian systems?
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What is the main advantage of multipoint instruments over single-point instruments?
What is the main advantage of multipoint instruments over single-point instruments?
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Which type of viscometer is suitable for use with both Newtonian and non-Newtonian systems?
Which type of viscometer is suitable for use with both Newtonian and non-Newtonian systems?
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What is the relationship between shear rate and shearing stress in a Newtonian system?
What is the relationship between shear rate and shearing stress in a Newtonian system?
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What is the purpose of extrapolating a line through a single point on the rheogram to the origin?
What is the purpose of extrapolating a line through a single point on the rheogram to the origin?
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What information is obtained from the difference in plastic viscosities for two separate downcurves?
What information is obtained from the difference in plastic viscosities for two separate downcurves?
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At what shear rates does the rheologic analysis of magnesia magma exhibit negative thixotropy or antithixotropy?
At what shear rates does the rheologic analysis of magnesia magma exhibit negative thixotropy or antithixotropy?
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How does dilatancy differ from antithixotropy in terms of solid dispersed phase volume?
How does dilatancy differ from antithixotropy in terms of solid dispersed phase volume?
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What is the formula to calculate the thixotropic coefficient, M, based on the plastic viscosities U1 and U2?
What is the formula to calculate the thixotropic coefficient, M, based on the plastic viscosities U1 and U2?
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When observing normal thixotropy, where does the downcurve appear in relation to the upcurve?
When observing normal thixotropy, where does the downcurve appear in relation to the upcurve?
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How does antithixotropy differ from rheopexy?
How does antithixotropy differ from rheopexy?
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What is the most suitable way to compare pseudoplastic systems?
What is the most suitable way to compare pseudoplastic systems?
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What is the significance of the exponent N in the equation FN = ƞ ‘G?
What is the significance of the exponent N in the equation FN = ƞ ‘G?
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What is the characteristic of dilatant flow?
What is the characteristic of dilatant flow?
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What is the difference between pseudoplastic and dilatant systems?
What is the difference between pseudoplastic and dilatant systems?
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What can be used to describe dilatancy in quantitative terms?
What can be used to describe dilatancy in quantitative terms?
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What is the term used to describe materials that exhibit an increase in resistance to flow with increasing rates of shear?
What is the term used to describe materials that exhibit an increase in resistance to flow with increasing rates of shear?
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What is rheology used to describe?
What is rheology used to describe?
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What type of systems can be described in terms of absolute viscosity?
What type of systems can be described in terms of absolute viscosity?
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What is the significance of rheology in pharmaceutical product development?
What is the significance of rheology in pharmaceutical product development?
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What are the two main classes of materials based on types of flow?
What are the two main classes of materials based on types of flow?
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Why is it important for manufacturers to understand rheology in producing medicinal and cosmetic products?
Why is it important for manufacturers to understand rheology in producing medicinal and cosmetic products?
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What is the relationship between viscosity and flow in a fluid?
What is the relationship between viscosity and flow in a fluid?
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What is the primary method of obtaining the area of hysteresis in a rheogram?
What is the primary method of obtaining the area of hysteresis in a rheogram?
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What is the significance of the time of holding before reducing shearing stress in a plastic system?
What is the significance of the time of holding before reducing shearing stress in a plastic system?
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What is the relationship between the plastic viscosities U1 and U2 in the equation for the thixotropic coefficient, M?
What is the relationship between the plastic viscosities U1 and U2 in the equation for the thixotropic coefficient, M?
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What is the purpose of determining the structural breakdown of a plastic system possessing thixotropy when subjected to increasing shear rates?
What is the purpose of determining the structural breakdown of a plastic system possessing thixotropy when subjected to increasing shear rates?
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What is the characteristic of a plastic system that exhibits thixotropy when subjected to a constant rate of shear?
What is the characteristic of a plastic system that exhibits thixotropy when subjected to a constant rate of shear?
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What is the equation that relates the thixotropic coefficient, M, to the plastic viscosities U1 and U2?
What is the equation that relates the thixotropic coefficient, M, to the plastic viscosities U1 and U2?
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What is a characteristic of materials that exhibit viscoelasticity?
What is a characteristic of materials that exhibit viscoelasticity?
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Which of the following pharmaceutical areas is rheology significant in?
Which of the following pharmaceutical areas is rheology significant in?
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What is an example of a pharmaceutical product that exhibits viscoelasticity?
What is an example of a pharmaceutical product that exhibits viscoelasticity?
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In which of the following pharmaceutical areas is rheology important for mixing and particle-size reduction?
In which of the following pharmaceutical areas is rheology important for mixing and particle-size reduction?
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What is a significant aspect of rheology in quasisolids?
What is a significant aspect of rheology in quasisolids?
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In which of the following pharmaceutical areas is rheology important for the flow of powders from hoppers?
In which of the following pharmaceutical areas is rheology important for the flow of powders from hoppers?
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What type of flow is typically exhibited by polymers in solution?
What type of flow is typically exhibited by polymers in solution?
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What does the yield value in a suspension indicate?
What does the yield value in a suspension indicate?
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In what kind of system does the consistency curve begin at the origin?
In what kind of system does the consistency curve begin at the origin?
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What is the impact of increasing the rate of shear on the viscosity of a pseudoplastic substance?
What is the impact of increasing the rate of shear on the viscosity of a pseudoplastic substance?
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Why does a pseudoplastic material not have a yield value like a plastic system?
Why does a pseudoplastic material not have a yield value like a plastic system?
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How can an apparent viscosity be calculated in a pseudoplastic material?
How can an apparent viscosity be calculated in a pseudoplastic material?
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Study Notes
Rheology
- Rheology is the science of the flow and deformation of materials, including liquids and solids.
- Viscosity is an expression of the resistance of a fluid to flow, with higher viscosity indicating greater resistance.
Fluidity (φ)
- Fluidity is the reciprocal of viscosity (φ = 1/η).
- It is a measure of the ease of flow of a fluid.
Kinematic Viscosity
- Kinematic viscosity is the absolute viscosity divided by the density of the liquid at a specific temperature.
- Units of kinematic viscosity are stoke (s) and centistoke (cs).
Absolute Viscosities of Newtonian Liquids
- Castor oil: 1000 cp
- Olive oil: 100 cp
- Water: 1.0019 cp (used as a standard for viscosity of liquids)
Temperature Dependence of Viscosity
- Viscosity of a liquid decreases as temperature increases.
- Fluidity increases with temperature.
- The dependence of viscosity on temperature is expressed by an equation analogous to the Arrhenius equation of chemical kinetics.
Non-Newtonian Systems
- Most pharmaceutical products are not simple liquids and do not follow Newton's law of flow.
- Examples include suspensions, emulsions, and gels.
Thixotropy
- Thixotropy is the property of a fluid that becomes less viscous when agitated and more viscous when left still.
- Thixotropy is measured by the area of the hysteresis loop in a rheogram.
Measurement of Thixotropy
- Two approaches to estimate the degree of thixotropy:
- Determine structural breakdown with time of a plastic system possessing thixotropy when subjected to a constant rate of shear.
- Determine structural breakdown of a plastic system possessing thixotropy when subjected to increasing shear rates.
Pseudoplastic Flow
- Pseudoplastic flow is typically exhibited by polymers in solution.
- The consistency curve for a pseudoplastic material begins at the origin, with no yield value.
- Viscosity of a pseudoplastic material decreases with increasing rate of shear.
Dilatant Flow
- Dilatant flow occurs in certain suspensions with a high percentage of dispersed solids.
- Resistance to flow increases with increasing rates of shear.
- Dilatant systems are often termed "shear-thickening systems."
Rheology in Pharmacy
- Rheology is significant in pharmacy in areas such as:
- Fluids: mixing, particle-size reduction, passage through orifices, and physical stability.
- Quasisolids: spreading and adherence on the skin, removal from jars, and release of the drug from the base.
- Solids: flow of powders from hoppers and into die cavities.
- Processing: production capacity and processing efficiency.
Viscoelasticity
- Viscoelastic measurements are based on the mechanical properties of materials that exhibit both viscous and elastic properties.
- Examples of viscoelastic systems in pharmacy include creams, lotions, ointments, and suspensions.
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Description
Test your knowledge on rheology, including topics such as Newtonian systems, Non-Newtonian systems, Plastic Flow, and more. Explore the flow of liquids and the determination of rheologic properties in pharmaceutical areas.
