Physical Chemistry

Question 1

How does a chain interact with its surroundings?

Answer 1

Polymers behave differently in different solvents

• used to predict the free volume

Question 2

Historical figures:

Answer 2

1. Staudinger (macromolecular hypothesis)
2. Kuhn (random coil and freely joint chains)
3. Flory (lattice models, solutions and swelling)
4. Edwards (excluded volume theories, melt viscoelasticity)
5. de Gennes (reptation theory, scaling laws)

Question 3

How does hydrodynamic volume of a coil change with solvent affinity and temperature?

Answer 3

As temperature increases, hydrodynamic volume increases (T change, changes affinity between solvent and polymer)

As solvent affinity increases, hydrodynamic volume increases (higher solvent affinity, chain spreads out to increase contact with the solvent)

Question 4

How is hydrodynamic volume measured?

Answer 4

• use the end-to-end distance (or radius of gyration)

Question 5

Different Levels of ideal chains

Answer 5

1. freely joint chains (chains of fixed length can rotate freely in space)
2. freely rotating chains (chains of fixed length have specified x-y angle)
3. Hindered rotation chain (chains of fixed length have specific x-y and x-z angle)

Question 6

What is the radius of gyration?

Answer 6

Calculation of the radius as the average distance from the center of mass to each molecule in the chain

Question 7

Example:
length is 1.54 A
theta is 109.5 degrees
thi is 120 degrees

for a chain of 1000 ethylene units, calculate R for:
a) freely joint
b) freely rotating
c) hindered rotation

Answer 7

a) 68.1A
b) 97.4A
c) 168.8A

Question 8

What is the Theta Condition?

Answer 8

The condition where polymers act as ideal coils

• the solvent and temperature interactions cancel out the inter-chain interactions
• at theta, gets a Tg and an accompanying C,inf (Tg is the lowest T before polymer begins to percipitate)

Question 9

What is the issue with ideal chains?

Answer 9

• does not have excluded volume (does not account for the fact that chains cannot occupy the same space) - chains attract each other until a certain point where they repulse each other

(cancels out interactions at theta condition)

Question 10

What is Lattice Structure?

Answer 10

• a method to account for no-overlapping molecules
• essentially creates a box with locations where molecules could be and can do this through random walk, avoiding overlapping

Question 11

What is Flory-Huggins solution theory

Answer 11

• to calculate the energy of mixing, add together the change in enthalpy/entropy of the polymer-polymer pairs, the solvent-solvent pairs and the resulting solvent-polymer pairs.
• creates a parameter X, which is the Flory Huggins parameter which looks at how the polymer and solvent interactions dominate the system
• X = 0.5: ideal chain
• X<0.5: polymer-solvent interactions are favoured (good solvent)
• X>0.5: polymer-polymer interactions are favoured (bad solvent)