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The pressure dependence of the Flory-Huggins interaction parameter of two binary polymer blends was investigated by small-angle scattering of neutrons (SANS). We studied deuteropolystyrenel poly(viny1 methyl ether) (d-PS/PVME) and deuteropolystyrene/poly(phenylmethylsiloxane) (d-PSIPPMS) exhibiting lower and upper critical solution temperatures, respectively. It turned out that in the investigated pressure range between 1 and 1200 bar the enthalpic contribution of the Flory-Huggins parameter is practically independent of pressure. On the other hand, the absolute value of the entropic contribution, which is related to the free volume of the blend, decreases with pressure. Furthermore, pVT data of the d-PS/PPMS blend and of ita components were measured. From the fits of these data with the Flory-Orwoll-Vrij (FOV) equation of state, the Flory-Huggins parameter was derived and compared with the SANS data. The comparison with the pressure dependence for the entropic contribution is unsatisfactory. The enthalpic contribution is almost pressure independent, as observed in the SANS data.

The use of neutrons in small-angle scattering has opened a wide field of applications for investigations in magnetism, polymeric science, for certain problems in biology, and in metallurgy. In the first part, this review deals with the experimental aspects of neutron small-angle scattering. In particular, the compensation of the relatively small luminosity of neutron sources as compared to X-ray tubes will be discussed in detail. This is mainly achieved by large beam cross sections, leading to correspondingly long instruments, and by an optimization of the intensity with respect to the different contributions to the resolution width of the scattering vector K(~: = 27r0/2, 0 = scattering angle, 2 = wavelength). Instruments which have been developed along these lines are described, especially the 40 m instrument in Ji~lich and the 80 m instrument at the high-flux reactor in Grenoble. The Grenoble instrument covers a range of scattering vectors between 1 .~-1 and 3.10 -4 A-~; the maximum possible resolution is about 10 -4 A-1. Typical applications are reviewed and discussed, namely those dealing with (i) density and compositional fluctuations in solids (alloys, defect clusters, dislocations, grains), (ii) magnetic inhomogeneities in solids (alloys, magnetic domains), (iii) flux-line lattices in type-II superconductors (form factors, imperfections and morphology), (iv) polymers in the solid state, and (v) biological substances.

Articles you may be interested inSmall-angle neutron scattering studies of polybutadiene/polystyrene blends as a function of pressure and microstructure: Comparison of experiment and theory Effect of the Onsager coefficient and internal relaxation modes on spinodal decomposition in the high molecular isotopic blend polystyrene/deuteropolystyrene studied with small angle neutron scattering 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 J. Chem. Phys. 97, 8775 (1992); 10.1063/1.463347 Shear stabilization of critical fluctuations in bulk polymer blends studied by small angle neutron scattering J. Chem. Phys. 93, 795 (1990); 10.1063/1.459533 Investigation of the phase diagram and critical fluctuations of the system polyvenylmethylether and d polystyrene with neutron small angle scatteringFor the isotopic blend of polystyrene (PS)/deutero PS (M w = 10 6 dalton), the Flory-Huggins interaction parameter X(rp,n was determined by means of the structure factor SeQ) measured by small angle neutron scattering (SANS). From X(rp,n, 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 Te. Furthermore, the transition ofthe 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.J. Chem. Phys. 93 (11).

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 Tf. 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 Tf both in the homogeneous and (ii) with Tf 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 Tf 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.