Critical fluctuations and relaxation phenomena in the isotopic blend polystyrene/deuteropolystyrene investigated by small angle neutron scattering

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Abstract
For the isotopic blend of polystyrene (PS) PS/deutero PS (M=106 dalton), the Flory–Huggins interaction parameter χ(φ,T) was determined by means of the structure factor S(Q) measured by small angle neutron scattering (SANS). From χ(φ,T), the miscibility gap and the corresponding spinodal line was evaluated with a critical temperature of 130 °C. Decomposition in the miscibility gap is extremely slow due to the critical slowing down and due to a glass transition 30 K below Tc. Furthermore, the transition of the homogeneous blend between two temperatures was investigated by SANS. The interdiffusion constant of the two isotopic species was determined from these experiments. Our results approach the Cahn–Hilliard–Cook theory only in the limit of small wavenumbers of the fluctuations. Three weeks after annealing the sample, demixing was observed in the predicted two-phase region.