Exam 1 Spring 17 Flashcards
Consistency can affect what?
flow of materials, mixing, choice of processing equipment, packaging into container, patient acceptability, physical stability, bioavailability, removal from container for use
Define viscosity
- resistance to flow
- internal friction of a system
How do you determine viscosity (via layers)?
strength that a layer exerts on adjacent layers determines the system viscosity
What is the rate of shear and what is the variable that denotes it?
Rate of shear = G = dv/dr
dv = displacement of each layer
dr = thickness of each layer
What is the shearing stress and what is the variable that denotes it?
Shearing stress = F = Force/A
Force applied / surface area of each layer
What is the relationship between rate of shear and shearing stress?
F ∝ G
In variables, what is Newton’s law of flow?
F = ηG
the more shearing stress = the more rate of shear
How does viscosity affect F and G?
The higher the viscosity, the greater is the shearing stress required to produce a certain rate of shear
What are the types of non-Newtonian flow?
- Plastic flow
- Pseudoplastic flow
- Dilatant flow
What is η?
Coefficient of Viscosity (poise)
In a rheogram, when you plot F vs G, you get a straight line/slop (direct relationship). What is the slope (in variable) and what does it represent?
1/η
- Represents fluidity (Φ)
In variables, define kinematic viscosity.
η/ρ
Viscosity/Density
What are the units for kinematic viscosity?
stokes = centipoise / [g/cm^3]
What are the characteristics of a rheogram of a Newtonian system?
Rate of shear (y) and shearing stress (x) are directly related
What are some examples of non-Newtonian systems?
ointments, suspensions, emulsions
What is another name for plastic flow?
Bingham bodies
What is a yield value?
f = the amount of force you have to apply to a non-newtonian fluid in order for it to move
What happens when shear stress doesn’t exceed yield value?
the material will act as an elastic material
How can you determine the yield value?
when shearing stress exceeds yield value, the relationship between F and G are proportion; extend the line of their slop and where it touches the x-axis is the yield value
What is the variable for plastic viscosity and how do you solve for it?
U = (F - f) / G
What are the contributions to yield value?
Vanderwaals forces and interparticle friction
What is an example of plastic fluid?
flocculated suspensions
What effect does flocculated suspensions have on yield values?
more flocculated = larger the yield value
What is another name for pseudoplastic flow?
Shear thinning systems