EARLY STATE OF SPINODAL DECOMPOSITION STUDIED WITH SMALL-ANGLE NEUTRON-SCATTERING IN THE BLEND DEUTEROPOLYSTYRENE AND POLYVINYLMETHYLETHER - A COMPARISON WITH THE CAHN-HILLIARD-COOK THEORY

The relaxation behavior of a polymer blend, deutero-polystyrene and polyvinylmethylether (d-PS/PVME) was studied by investigating the equilibrium structure factor S(Q) and its time dependence S(Q,t) after the blend had been exposed to a rapid temperature step from T0 to T(f) The structure factor S(Q,t) was determined as a function of scattering vector Q by time-resolved neutron scattering experiments. Two cases were investigated (i) with T0 and T(f) both in the homogeneous and (ii) with T(f) in the unstable region of the phase diagram. The relaxation was compared with the Cahn-Hilliard-Cook theory. The strongly Q-dependent (nonlocal) Onsager coefficient was determined from the relaxation time and compared with predictions by Pincus et al The self-diffusion constants of the components were obtained for Q-->0. Finally, the experiments at T(f) led to the critical behavior of the susceptibility S(Q=0) near the spinodal. An Ising-type critical behavior was observed across the (extrapolated) spinodal.