Physical Chemistry and Solutions

Question 1

Flory-Huggins solution theory, how does X change with temperature?

Answer 1

X is inversely proportional to Temperature

Question 2

What is the alpha factor in the Flory-Huggins solution theory?

Answer 2

• its the expansion factory, calculated as the end-to-end distance divided by the theta condition end-to-end distance
• a>1: T>T,theta
• a<1: T<T,Theta
• a=1: T=T,theta

Question 3

What is the region below T,theta called?

Answer 3

The coil-gobule transition reagion

• chains collapse on each other
• chains start to percipitate

Question 4

How can you experimentally find T,theta?

Answer 4

Find the temperature when the polymer percipitates (solution becomes cloudy), Tc

• plot 1/Tc by 1/sqrt(M), the intercept is 1/T,theta

Question 5

How does concentration affect solution behaviour?

Answer 5

2 main changes:

1. changes viscosity (changes chain interaction behaviour) - increases with concentration
2. changes phase separation behaviour (changes amount of solute that can dissolve)

Question 6

What is Overlap concentration, C*?

Answer 6

The concentration at which hydrodynamic volumes begin to overlap

Question 7

How does solubility change with temperature?

Answer 7

Get phase transitions
- at high temperature have single phase
- at low temperatures have single phase
- in between in a 2 phase region where percipitation occurs

**these regions change with molecular weight

Question 8

Upper Critical solution temperature (UCST)

Answer 8

• this is the highest temperature that a 2 phase region can exist
  – can be broken up into the metastable region (where some regions are just polymer and others are just solvant) occurs right below the UCST
  – the bisodol region where it gradually moves to 2-phase by forming small islands of polymer concentration
  – the spinsdol region - just becomes 2-phase

**kinetics change depending on if its bisodol or spinsdol

Question 9

Lower critical solution temperature (LCST)

Answer 9

– temperature above the ucst see another phase separation (only occurs with some polymers, not all)

– occurs becasue chain-solvent interactions become unfavourable again as Van Deer Waals or hydrogen forces break the chain-solvent bonds apart
– not accounted for by flory

Question 10

What is Reptation?

Answer 10

The concept of excluded volume to chain entanglement and motion

• is the idea that a boundary tube surrounds the polymer chain attempting to be moved. The chain must escape through the tube and detangle from all the chain-chain bonding and interlapping chains around it
• chains must diffuse out of this volume
• similar to how snakes will entangle themselves

Question 11

What is reptation time proportional to?

Answer 11

• the number of links in the chain (cubed)
• it is also related to the temperature as it changes the amount of energy in the system for movement of chains + increased free volume