36 Questions
Which class of materials exhibit both viscous properties of liquids and elastic properties of solids?
Viscoelastic materials
In pharmacy, which of the following systems belong to the viscoelastic class?
Creams, lotions, and suspensions
Which pharmaceutical area is rheology significant for the physical stability of disperse systems?
Fluids
For which pharmaceutical area is rheology significant in the capacity of solids to mix with miscible liquids?
Quasisolids
What happens as the degree of dilatancy increases?
N decreases
What type of systems show a displacement of the downcurve to the left of the upcurve in rheograms?
Pseudoplastic systems
What is thixotropy defined as?
A slow recovery of consistency through shearing
What is the relationship between rheograms obtained with thixotropic materials and the rate of shear?
They are highly dependent on the rate of shear
What does the thixotropic coefficient, M, represent?
The loss in shearing stress per unit increase in shear rate
What does negative thixotropy or antithixotropy refer to?
An increase in viscosity with increased time of shear
How does negative thixotropy differ from dilatancy?
Negative thixotropy involves low solids content, while dilatancy involves high solids content
How is the thixotropic coefficient, M, calculated?
$M = \frac{v2 \ln (v2)}{v1 \ln (v1)}$
What type of materials exhibit plastic flow according to the text?
Colloidal solutions
What is the property of a Bingham body that distinguishes it from other materials in terms of flow?
It has a yield value
What property is analogous to fluidity in Newtonian systems for non-Newtonian materials?
Mobility
What equation describes plastic flow, as mentioned in the text?
$U = 𝐹− 𝑓𝐺$
What is the hysteresis loop used to measure?
Degree of thixotropy
How is the thixotropic coefficient, B, calculated?
$\frac{U_1-U_2}{\ln(t_2/t_1)}$
What does the area between the up curve and down curve of a rheogram represent?
Degree of thixotropy
What is the significance of determining the structural breakdown of a plastic system possessing thixotropy?
Assessing the degree of thixotropy
What happens to the system as the degree of dilatancy increases?
The system becomes more viscous and less elastic
What behavior is observed in Newtonian systems when the rate of shear is reduced after reaching the maximum?
The down curve is identical to the up curve
What does thixotropy refer to in rheology?
The fast recovery of consistency after shearing
How are rheograms obtained with thixotropic materials affected by the rate of shear?
They are highly dependent on the rate at which shear is increased or decreased
What is the primary purpose of using a planimeter or other suitable technique in rheology?
To measure the area between the up curve and down curve of a rheogram
What is the thixotropic coefficient, B, used to calculate?
The rate of breakdown with time at constant shear rate
In rheology, what does the term 'structural breakdown' refer to?
The breakdown of a plastic system when subjected to increasing shear rates
How is the thixotropic coefficient, M, calculated in relation to the plastic viscosities of the two downcurves?
$\frac{U_1 - U_2}{ln(t_2/t_1)}$
What is the significance of the yield value in a plastic system?
It indicates the force of flocculation in the suspension
What distinguishes pseudoplastic flow from plastic flow in terms of rheology?
Pseudoplastic flow exhibits no yield value, while plastic flow does
How is the viscosity of a pseudoplastic material different from that of a plastic system?
Pseudoplastic material has a constant viscosity, while plastic systems' viscosity varies with shear rate
What can be inferred about the relationship between rheograms obtained with thixotropic materials and the rate of shear?
The rheograms exhibit non-linear behavior with varying rates of shear
What is the practical significance of analyzing the rheologic properties of pharmaceutical products?
It can influence the selection of processing equipment
How are simple liquids different from heterogeneous dispersions in terms of rheologic properties?
Heterogeneous dispersions can be described by a single value of absolute viscosity
What does the term 'rheology' specifically refer to?
The science of flow and deformation of solids and liquids
In rheology, what is the significance of the term 'viscoelasticity'?
It involves both viscous properties of liquids and elastic properties of solids
Test your knowledge of rheology and its key concepts in Chapter 19. Explore topics such as dilatancy and thixotropy to better understand the behavior of substances under varying shear rates.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
