Rheology Lecture Flashcards
Define Rheology
Flow of liquids and the deformation of solids
Define viscosity
Resistance of a fluid to flow
^ then resistance ^
- Poise & centipoise
Define Newtonian flow
Constant viscosity with the change in shear rates
- top layer moves at a constant velocity
- lower layer velocity is directly proportional to its distance from fixed bottom layer
Define Non-Newtonian System
Variable viscosity with increasing shear rate
- Plastic, pseudoplastic and dilatant
Define rate of shear
Difference in velocity between two planes of liquid separated by the distance
- mobility of a liquid
Define shearing stress
Force per unit area applied to the top layer to push the liquid to flow
- Forced applied during shaking
Graphs?
Shearing stress increases with rate of shear
Viscosity does not change with shear rate
Define Rheograms
Polot of shear rate as a function of shear stress
- “Consistency curve or flow curve”
Newtonian system’s rheogram?
Straight line through origin
- Slope = fluidity
Define fluidity
Reciprocal of viscosity
Define kinematic viscosity
Absolute viscosity divided by density of the liquid at a specific temperature
- stoke and centistoke
Define Plastic flow
Bingham bodies do not begin to flow until a specific shearing rate (yield value) is exceeded
- Like elastic materials
- Slope = mobility
Reciprocal of mobility?
Plastic viscosity
Plastic flow graphs
Shearing stress increases as rate of shear increase
Shear rate increases as viscosity decreases and levels out
Define Pseudoplastic flow
No yield value
Rheogram begins at origin
- Viscosity decreases with increasing shearing rate
- “Shear thinning material” –> viscosity decreases (gets thinner) with increasing shear rate
- Not linear
- Decreased viscosity
Psuedoplastic flow graph
N=1 Newtonian; other than that non-newtonian
Shearing stress increases to a point of straight up as rate of stear increases
Shear rate increases as viscosity decreases and levels out
- Curves not lines
Define shear thickening system dilatant materials
- Materials’ volume increases under applied force (dilatant)
- Increase in viscosity with increasing rate of shear
- More effort into stirring the more difficult to stir.
Dilatant Flow Graphs
Shearing stress increases with rate of shear steeply and then begins to level out
Shear rate increases to a point of straight up as viscosity slowly and then abruptly
Define thixotropy
Becomes more fluid with increased time of applied force
- “work softening”
- Reversible
- Exhibits shear thinning
Define rheopexy
Solid forms a gel readily upon shaking than when the material is kept at rest
- More viscous with increasing time of applied force
- “Work-hardening”
Pseudoplastic and plastic rheograms
Down curve to the left of up curve
Dilatant material rheogram
Down curve to the right of up curve
Viscosity in Newtonian systems?
Single shear rate
Viscosity for non-Newtonian systems?
Variable shear rate
Define bio-rheology
Study of deformation and flow in the biological systems
Define hemorheology
Deals with flow properties of blood
Bloooooooood?
Non-newtonian fluid
Flow determined by hematocrit and plasma viscosity
Rheological properties of mucus?
Diagnostic tool
