Thesis presented October 06, 2003

Abstract:
The origin and signatures of the concentration dependent Flory χ(eƒƒ) -parameter for neutral water-soluble polymers are studied. The three versions of two-state model proposed previously to explain the phase behavior of Poly(ethylene oxide) in water lead to χ(eƒƒ)(Φ) . This dependence can serve as a useful diagnostic of the performance of models: it allows to distinguish between different models and test involving parameters. The emergence of χ(eƒƒ)(Φ) from alternative single-state models is also discussed. The macroscopic signatures of χ(eƒƒ)(Φ) are illustrated on the example of swelling of isolated coils and planar brushes. The Φ dependence of χ(eƒƒ) in systems with uniform concentration gives rise to two main consequences: a shift in the crossover between Gaussian and self-avoidance regimes, and a possibility of a first-order collapse transition for isolated flexible coils. χ(eƒƒ)(Φ) can lead to a vertical phase separation in polymer brushes involving coexistence of two phases of finite concentration. This approach is applied to the interpretation of indirect evidence that Poly(N-isopropylacrylamide) brushes exhibit this effect.


Keywords:
PEO, PNIPAM, polymer brushes, neutral water soluble polymers

On-line thesis. ​