W10 Applied Rheology

Question 1

What is the definition of Rheology?

Answer 1

– Study of the flow and deformation of matter (fluids)
– The term rheology originates from the Greek word “rheos” translating as “a flowing, stream, current” and “logy” meaning “the study of”

Question 2

What is the definition of viscosity?

Answer 2

– The resistance to flow, i.e. if viscosity is high
then flow is reduced

Question 3

What is the “Shear”?

Answer 3

-The relative motion between adjacent layers of a moving fluid

Question 4

Viscosity is inversely related to..

Answer 4

Temperature

Question 5

Rate of flow is directly proportional to..

Answer 5

Applied stress

Question 6

Order the following in terms of increasing viscosity at 20°C:
Ethanol
Water
Chloroform
Glycerol

Why is this?

Answer 6

Chloroform < Water < Ethanol < Glycerol

Glycerol has the most OH so can form more hydrogen bonds

Question 7

What are Newtonian fluids?

Answer 7

They obey the relationship where
Shear stress = Viscosity x Shear rate
represented on a straight line graph

Question 8

What is “Shear thinning”?

Answer 8

Fluids often decrease in viscosity with increasing
shear rate.

Question 9

What is Shear-thickening/ Dilatant/Pseudoplastic flow?

Answer 9

Some fluids increase in viscosity with increasing
shear rate.

Question 10

Plastic (or Bingham) flow:

Answer 10

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

Question 11

What is the relationship between Polymer concentration and viscosity?

Answer 11

• Viscosity increases with polymer concentration

Question 12

Polymer concentration and viscosity

Answer 12

• Low concentration
  – Isolated polymer chains, shape & volume determined by polymer-
  solvent and intra-polymer interactions
• High concentration (network solution)
  – Inter-penetrating chains
  – polymer movement hindered by neighboring chains
  – Inter- and intra- polymer interactions important

Question 13

Capillary Viscometer

Answer 13

• Only used for determining the viscosity of Newtonian liquids
• Flow through a thin tube is measured under gravity
• Apparatus can be clamped in a water bath at desired temperature
• Flow time should be around 200 seconds
• Repeated until 3 readings within 0.5 seconds are achieved

Question 14

Rotating Viscometer

Answer 14

• Used for determining the viscosity of Newtonian and Non-Newtonian liquids
• Measure drag exerted on a body when rotated in a fluid