Term
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Definition
| The study of the flow of matter, primarily in the liquid state, but also as 'soft solids' or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force |
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Term
| Define Newtonian classification of fluid |
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Definition
| Newtonian fluids can be characterized by a single coefficient of viscosity for a specific temperature. |
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Term
| Define non-Newtonian classification of fluid |
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Definition
| Fluids with strain rate dependent viscosity |
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Term
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Definition
| A fluid characteristic by becoming more viscous when shaken or agitated |
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Term
| Define and describe viscosity |
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Definition
-The resistance to flow
-Internal friction of a system
-Strength that a layer exerts on adjacent layers |
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Term
| In the Newtonian law of flow, what is dr and what is dv? |
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Definition
dr = thickness of imaginary infinite layers of the cube of liquid
dv = velocity |
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Term
| Give the equation for the rate of shear for Newtonian flow |
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Definition
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Term
| What is the Newtonian law of flow? |
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Definition
F=ηG
F=shearing stress=Force/a
G=rate of shear
η=coefficient of viscosity |
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Term
| If the relationship between F (shearing stress) and G (rate of shear) is direct, what kind of flow does the fluid demonstrate? |
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Definition
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Term
| Give three examples of Non-Newtonian flow |
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Definition
| Plastic, pseudoplastic, and dilatant |
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Term
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Definition
The reciprocal of viscosity (1/η)
The slope of shearing stress (F) vs rate of sheer (G), if Newtonian |
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Term
| Give the equation for kinematic viscosity |
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Definition
Viscosity/Density
(measured in centistokes) |
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Term
| Define poise and what units it is measured in |
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Definition
The force required to move two adjacent layers of liquid across each other, if they are 1 cm apart, at a speed of 1 cm/s
units= g/(cm x sec) |
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Term
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Definition
| Substances characterized by plastic flow |
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Term
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Definition
| Like fluidity, but for Non-Newtonian flow |
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Term
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Definition
The shearing stress required for the substance to yield to force.
Below f, substance acts as a solid, elastic material. |
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Term
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Definition
A material that, when F is greater than f, it is Newtonian.
f=yield value, F=shearing stress |
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Term
| Give the equation for plastic viscosity. What units is it measured in? |
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Definition
The inverse of mobility
Plastic viscosity, U= (F-f)/G
Units are in poise |
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Term
| If a suspension is more flocculated, is the yield value increased or decreased? |
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Definition
The yield value is increased. (flocculation ∝ yield value)
Yield value increases with van der Waals forces and interparticle friction |
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Term
| Give an example of a plastic material |
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Definition
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Term
| Define pseudoplastic flow |
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Definition
| A fluid that is not completely plastic, but show some plasticity |
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Term
| How is apparent velocity calculated using a graph of pseudoplastic flow? |
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Definition
| Apparent viscosity at a given F is determined by a slope of tangent at that point |
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Term
| Using the formula FN=η'•G , what does it mean when N=1? |
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Definition
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Term
| Give a pharmaceutical example of pseudoplastic material |
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Definition
Natural and synthetic gums (tragacanth, Na-alginate, methylcellulosa, Na-CMC)
Or even cornstarch in water |
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Term
| Why is the rheogram of a pseudoplastic material curved? |
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Definition
-Shear force aligns polymers along their long axis, reducing internal resistance to flow
-Uncoiling releases entrapped solvent |
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Term
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Definition
| Increasing shearing force increases resistance to flow |
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Term
| Give an example of a pharmaceutical use of dilatant flow |
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Definition
| Liquid bandages, pastes (very concentrated suspensions) |
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Term
| Using the formula FN=η'•G , what does it mean when N<1? |
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Definition
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Term
| What are some characteristics of suspensions with dilatant flow? |
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Definition
-High percentage of dispersed solids (>50%)
-Small, deflocculated particles
-Will break a blender |
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Term
| Why do highly concentrated suspensions dilate? |
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Definition
-Under stress, the material takes on open form of packing with increased interparticle void volume
-Vehicle remains constant, therefore wetting decreases |
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Term
| What viscometers are for Newtonian flow only? |
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Definition
Capillary and falling sphere
(One-point systems, single shearing stress) |
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Term
| What viscometers can be used for non-Newtonian flow? |
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Definition
Cup & Bob, Cone & Plate
(Can operate at multiple shearing stresses) |
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Term
| How does a Capillary viscometer (Ostwald) work? |
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Definition
| It measures the time required for the liquid to pass between two marks as a flows through a vertical capillary tube. The measurement is compared with water to obtain relative viscosity. |
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Term
| How does a falling ball viscometer (Hoeppler) measure viscosity? |
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Definition
It measures the rate at which a ball falls through a sample liquid
A water jacket outside the tube makes the temperature constant |
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Term
| What formula calculates viscosity, as obtained by a falling ball viscometer? |
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Definition
η= t(Sb-Sf)B
t=time
Sb-Sf= specific gravity difference
B=constant |
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Term
| How does a Cup and Bob viscometer work? |
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Definition
| By putting the sample in between the cup and bob, and rotating one. The torque from the drag is measured. |
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Term
| What is a disadvantage to a Rotovisco viscometer? |
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Definition
"Plug flow", that shearing stress decreases with the distance from the rotating bob to the side of the stationary cup.
Therefore, use as big a bob as possible. |
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Term
| What happens when shearing stress is removed from a plastic system? |
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Definition
Hysteresis loop- it remains slightly less viscous even after the stress is withdrawn
[image] |
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Term
On a rheogram:
What are the axis?What does the slope indicate? |
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Definition
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Term
| What happens when shearing stress is removed from a pseudoplastic system? |
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Definition
| Some "memory" of the force is retained; thixotropy |
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Term
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Definition
An isothermal and comparatively slow recovery, on standing of a material, of a consistency lost through shearing
Like a "memory" |
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Term
| What two things are rheograms of thixotropic systems dependent on? |
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Definition
1. Rate at which stress is applied or removed
2. Length of time the material is subjected to stress |
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Term
| What kind of system is thixotropy applicable to? |
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Definition
| Shear-thinning systems only |
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Term
| In thixotropy, what is the technical term for the loose network breaks resulting in shear thinning? |
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Definition
| Gel-to-sol transformation |
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Term
| In thixotropy, why is it than when the stress is removed the structure does not instantly harden? |
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Definition
| The asymmetric particles counter the forces of Brownian motion |
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Term
| What is negative thixotropy? |
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Definition
Increase in consistency as the rate of shear decreases
Gel-like, great suspendability, and is easily pourable |
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Term
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Definition
Rheoplexy is to dilatant flow what thixotropy is to plastic and uniplastic flow
A phenomenon in which a solid forms a gel more readily when greatly shaken; gel is the equilibrium state |
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Term
| Give an example of a substance that demonstrates negative thixotropy |
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Definition
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Term
How do you measure thixotropy?
(Just memorize; don't need to know math.) |
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Definition
By building hysteresis loops and measuring either:
1. Structural breakdown with a constant rate of shear
2. Structural breakdown with increasing shear |
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Term
| What factor determines the level of thixotropy? |
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Definition
Thixotropic coefficient (mathematically derived from a hysteresis loop)
(We don't need to know how to do this math) |
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Term
| List some pharmaceutical applications to thixotropy |
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Definition
1. Poloxamers (dermatological gels)
2. Opthalmic polymers (shear thinning during blinking) |
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Term
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Definition
Brand name: pluronics
Clear, nontoxic, water-based gels as a dermatological base. Become non-Newtonian at high temp/conc |
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Term
| What is the formula for activation energy to start flow? |
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Definition
η=A•e^(Ev/RT)
or
ln(η)= ln(A) + (Ev/R)•(1/T)
(Modified Arrhenius equation)
A=constant
Ev=activation energy required
T=temp in Kelvin
R=gas constant |
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Term
| When plotting ln(η) versus (1/T), what is the slope of the line? |
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Definition
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Term
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Definition
Having both elastic (solid) and viscous properties
A quality of pharmaceuticals |
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Term
| Define elasticity, mathematically |
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Definition
Elasticity=stress/strain
E=F/γ
(Hooke's law) |
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Term
| Give some examples of viscoelastic materials |
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Definition
| Creams, lotions, ointments, suspensions, suppositories, blood |
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Term
| What quantifiable quality provides the pschorheologic quality "body"? |
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Definition
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Term
| What quantifiable quality provides the pschorheologic quality "slip"? |
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Definition
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Term
| What quantifiable quality provides the pschorheologic quality "spreadability"? |
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Definition
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Term
| What quantifiable quality provides the pschorheologic quality "feel"? |
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Definition
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Term
| What quantifiable quality provides the pschorheologic quality "sensory satisfaction"? |
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Definition
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