3. In the early days, before the development of the Flory-Huggins equation, scie

Question

3. In the early days, before the development of the Flory-Huggins equation, scientist had difficult time accounting for the peculiar mixing behavior of polymers. Probably the most dominant error was in the treatment of the entropie term in calculating the Gibbs free energy What is the physical reason that the entropy must be described differently than for example, an ideal gas? The Flory-Huggins equation was derived as a lattice model. List at least three limitations in using a lattice model for a polymer solution. Name a polymer and solvent that you would expect to be well-deseribed using the Flory-Huggins equation, and the reason that you think this.

Explanation / Answer

Entropy is described diffrently because in case of ideal gas there is no interaction between the molecules of ideal gas but in general this may not be the case.

Limitations:

1)Fluctuations are completely neglected.

2) At low concentration, which have dominating fluctuations, the theory is only appropiate very close to theta point.

3)It will work well for medium and high concentrations which do not exhibit strong density fluctuations.

Example: polystyrene in cyclohexane.

Reason: It do not exhibit strong density fluctuations.

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