Polymers: Polyelectrolytes, Viscosity & Rheology

Question 1

What are polyelectrolytes?

Answer 1

Polymers which have ionisable functional groups (charged)

Question 2

What are the 3 different types of polyelectrolyte?

Answer 2

1. Cationic (+) polyelectrolyte = polybases
2. Anionic (-) polyelectrolyte = polyacids
3. Amphoteric (+/-)polyelectrolyte = polyampholytes

Question 3

How do polyelectrolytes become anionic?

Answer 3

Ionisation

e.g. COOH functional group of chain becomes COO- + H+

Question 4

How do cationic molecules become soluble in water?

Answer 4

They become ionised/protonated

e.g. NH2 +H+ = NH3+

Question 5

Why are cationic polyelectrolytes insoluble in water when uncharged?

Answer 5

They are slightly crystalline due to a large umber of hydrogen bonds within the molecule

Question 6

What is the isoelectric point (IEP)?

Answer 6

The pH at which the effective net charge on a macromolecule is 0

Question 7

What is the charge of a polyampholyte affected by?

Answer 7

pH

Question 8

Define: Viscosity

Answer 8

The measure of a material’s resistance to flow

It is a result of the internal friction of the material’s molecules

Question 9

List the 4 conformations (shapes) of macromolecules in solution

Answer 9

1. Globule
2. Statistical coil
3. Rigid rod
4. Helix

Question 10

What does a macromolecule’s conformation depend on?

Answer 10

The chain flexibility and polymer-solvent interactions

Question 11

Describe the statistical coil conformation

Answer 11

Very swollen

Lots of solvent molecules inside

Question 12

Describe the rigid rod conformation

Answer 12

When the macromolecule is fully stretched

Question 13

When is the statistical coil conformation formed?

Answer 13

Only when the polymer is in a certain solvent = thermodynamically ideal solvent

Question 14

When does an unfolded chain conformation form?

Answer 14

In a thermodynamically good solvent

Question 15

When is the globule conformation formed?

Answer 15

In a thermodynamically poor solvent

Question 16

When does an aggregate of globules form?

Answer 16

In a non-solvent

Question 17

When is a solution at its most viscous?

Answer 17

When its polymers are in an unfolded chain conformation

It is at its least viscous when its polymers form an aggregate of globules

Question 18

Define: Rheology

Answer 18

The study of the flow and deformation properties of matter

Question 19

Define Newton’s Law

Answer 19

γ = σ/η

Question 20

What do the symbols in Newton’s Law represent?

Answer 20

γ = shear rate (s-1)
σ = applied stress (N)
η = dynamic (absolute) viscosity (Nm-2s)

Question 21

What is a Newtonian fluid?

Answer 21

A fluid in which the viscous stresses arising from its flow, at every point, are linearly proportional to the local strain rate = the rate of change of its deformation over time
i.e. Shear rate is linearly proportional to shear stress

Question 22

What is a non-Newtonian fluid?

Answer 22

A fluid whose properties differ in any way from a Newtonian fluid

Question 23

List the 3 types of solution viscosity

Answer 23

1. Relative viscosity
2. Specific viscosity
3. Reduced viscosity

Question 24

How does pH affect the viscosity of a polyanion?

Answer 24

Increased pH = reduced viscosity

Question 25

How does pH affect the viscosity of a polycation?

Answer 25

Increased pH = increased viscosity

Question 26

How does pH affect the viscosity of polyampholyte?

Answer 26

Most viscous at IEP = isoelectric point = overall charge on molecule is 0

Question 27

Describe the properties of alginates

Answer 27

• Sodium and potassium alginates are soluble in water

- They spontaneously form physical gels upon contact with divalent metal ions (e.g. calcium, zinc, etc)

Question 28

What is an alginate?

Answer 28

An anionic polysaccharide

Question 29

How does Gaviscon work?

Answer 29

• By forming a gel raft (thick layer) on top of the stomach contents soon after it has come into contact with the acid
• The raft acts as a strong physical barrier and helps keep all the components the stomach, not letting them seep back up the oesophagus where they cause discomfort

Question 30

List 3 types of non-Newtonian flow

Answer 30

1. Dilatant flow
2. Simple pseudoplastic flow
3. Simple plastic flow

Question 31

Describe plastic flow

Answer 31

Plastic flow is associated with the presence of flocculated particles in concentrated suspensions

Question 32

Describe pseudoplastic flow

Answer 32

Typically exhibited by polymers in relatively concentrated solutions

Question 33

Describe dilatant flow

Answer 33

Dilatant flow is exhibited by certain suspensions with a high percentage of dispersed solids