Rheology Lecture

Question 1

Define Rheology

Answer 1

Flow of liquids and the deformation of solids

Question 2

Define viscosity

Answer 2

Resistance of a fluid to flow
^ then resistance ^
- Poise & centipoise

Question 3

Define Newtonian flow

Answer 3

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

Question 4

Define Non-Newtonian System

Answer 4

Variable viscosity with increasing shear rate

- Plastic, pseudoplastic and dilatant

Question 5

Define rate of shear

Answer 5

Difference in velocity between two planes of liquid separated by the distance
- mobility of a liquid

Question 6

Define shearing stress

Answer 6

Force per unit area applied to the top layer to push the liquid to flow
- Forced applied during shaking

Question 7

Graphs?

Answer 7

Shearing stress increases with rate of shear

Viscosity does not change with shear rate

Question 8

Define Rheograms

Answer 8

Polot of shear rate as a function of shear stress

- “Consistency curve or flow curve”

Question 9

Newtonian system’s rheogram?

Answer 9

Straight line through origin

- Slope = fluidity

Question 10

Define fluidity

Answer 10

Reciprocal of viscosity

Question 11

Define kinematic viscosity

Answer 11

Absolute viscosity divided by density of the liquid at a specific temperature
- stoke and centistoke

Question 12

Define Plastic flow

Answer 12

Bingham bodies do not begin to flow until a specific shearing rate (yield value) is exceeded

• Like elastic materials
• Slope = mobility

Question 13

Reciprocal of mobility?

Answer 13

Plastic viscosity

Question 14

Plastic flow graphs

Answer 14

Shearing stress increases as rate of shear increase

Shear rate increases as viscosity decreases and levels out

Question 15

Define Pseudoplastic flow

Answer 15

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

Question 16

Psuedoplastic flow graph

Answer 16

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

Question 17

Define shear thickening system dilatant materials

Answer 17

• Materials’ volume increases under applied force (dilatant)
• Increase in viscosity with increasing rate of shear
• More effort into stirring the more difficult to stir.

Question 18

Dilatant Flow Graphs

Answer 18

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

Question 19

Define thixotropy

Answer 19

Becomes more fluid with increased time of applied force

• “work softening”
• Reversible
• Exhibits shear thinning

Question 20

Define rheopexy

Answer 20

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”

Question 21

Pseudoplastic and plastic rheograms

Answer 21

Down curve to the left of up curve

Question 22

Dilatant material rheogram

Answer 22

Down curve to the right of up curve

Question 23

Viscosity in Newtonian systems?

Answer 23

Single shear rate

Question 24

Viscosity for non-Newtonian systems?

Answer 24

Variable shear rate

Question 25

Define bio-rheology

Answer 25

Study of deformation and flow in the biological systems

Question 26

Define hemorheology

Answer 26

Deals with flow properties of blood

Question 27

Bloooooooood?

Answer 27

Non-newtonian fluid

Flow determined by hematocrit and plasma viscosity

Question 28

Rheological properties of mucus?

Answer 28

Diagnostic tool