Abstract
The phase behavior of a low molecular weight (MW = 4000) diblock copolymer of polystyrene and poly(ethylene oxide), PS−PEO, in the bulk as well in aqueous, D2O, solutions has been studied using small-angle neutron-scattering, dynamic and static light-scattering, and rheological methods. At low temperature the pure block copolymer forms a lamellar mesophase driven by the crystallization of PEO. The melting point of PEO, T ≈ 64 °C, is correspondingly accompanied by an order-to-disorder transition. The melt is typified by single-exponential depolarized correlation functions in the dynamic light-scattering spectra, observed in the temperature range 60 to 100 °C. Neutron scattering fails to show concentration fluctuations in the amorphous, disordered phase due to lack of contrast. In aqueous solutions up to roughly 20% polymer concentration, PS−PEO self-associates into spherical micelles with a core size of Rc ≈ 56 A and an interaction radius Rhs ≈ 115 A, corresponding to an aggregation number of 470. The hydr...
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