Polymers applied rheology

Question 1

Rheology

Answer 1

• Study of the flow and deformation of matter and fluids

Question 2

Viscosity

Answer 2

Resistance of flow, if viscosity is high then flow is reduced
- Units N s m^-2 or Pa.s
- Inverse relationship with temperature

Question 3

Effect of viscosity forces

Answer 3

• When force is applied there is a relative movement of fluid which is called shear
• Where force is applied it moves the fastest whereas futher down its stationary

Question 4

Applied stress formula

Answer 4

ETA x Rate of flow
- ETA is the dynamic viscosity

Question 5

Shear rate

Answer 5

• Velocity gradient of the height in the imaginary block of fluid so velocity gradient is divided by height
• Distance per time units
• Velocity m per s /m = s^-1 units

Question 6

Shear stress

Answer 6

Force applied (N / Area of upper surface of the block)
- N m^-2 units

Question 7

Factors that increase viscosity

Answer 7

• Molecules that can form hydrogen bonds are more viscous harder to break appart
• Chain cause more steric hinderence hydroxyl groups
• Greater molecular weight
• Greater concentration of polymers interaction

Question 8

Newtonian fluids

Answer 8

• Syrup BP (66% glycerol in water)
• Water
• Ethanol

Question 9

Rheograph

Answer 9

• X axis shear rate
• Y axis shear stress
• Linear positive line and gradient is viscosity
• Fluids that obey this are newtonian

Question 10

Non Newtonian fluids

Shear thinning

Answer 10

• Methylcellulose in solution
• Fluids decrease in viscosity with the increase in fluid rate

Question 11

Non Newtonian fluids

Shear thickening

Answer 11

• Increasing in viscosity with increasing shear force
• Shear thickening dilatant

Question 12

Pseudoplasic flow

Answer 12

• High molecular weight so molecules in solution become entangled therefore resists flow
• Shaking of bottle shear stress untangles and allign with the direction of flow

Question 13

Bingham flow (plasic)

Answer 13

• Some fluids only flow after a certain amount of shear stress has been applied

Question 14

How to test for viscosity

Answer 14

• Use a capillary viscometer for newtonian liquids
• Use rotating viscometer for determining the viscosity of newtonian and non newtonian

Question 15

Capillary viscometer

Answer 15

• For newtonian liquids
• Flow through thin tube measured under gravity
• Clamed in water bath at desired temp
• Flow time is around 200s
• Repeat for 3 readings withing 0.5s of eachother

Question 16

Rotating viscometer

Answer 16

• For newtonian and non newtonian
• Measures drag exerted on the body when fluid is rotated