T. Springer

Investigation of the hydrogen mobility in a mixed perovskite: Ba[Ca(1+x)/3Nb(2−x)/3]O3−x/2 by quasielastic neutron scattering

Abstract Quasielastic neutron scattering was applied to investigate the protonic motion in water-doped Ba[Ca 0.39 Nb 0.61 ]O 2.91 between 5 and 700 K. The backscattering spectra in the μeV-region for small scattering vectors Q lead to the protonic self-diffusion constant. The results were compared with measurements of the electrical conductivity. At larger Q , the spectra reveal two superimposed quasielastic components probably related to two groups of jump rates. Low resolution measurements indicate a rapid rotation of the hydroxyl groups.

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 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.

Investigation of the phase diagram and critical fluctuations of the system polyvenylmethylether and d‐polystyrene with neutron small angle scattering

The system PVME/d‐PS has been investigated by neutron small angle scattering. By extrapolating the critical scattering, the spinodal was determined and used to calculate the Flory–Huggins parameter χ(φ,T) in the frame of mean field theory. Separating the Gibbs potential of mixing ΔG in a Flory–Huggins term χ(φ,T) and a configurational term for the entropy ΔS, it turns out that χ is independent of the molecular weight, and of the weight distribution, i.e., it is a local or ‘‘segmental’’ quantity. The critical scattering was carefully investigated at the critical concentration. At temperatures Tc−T>2.4 K(Tc=141.9 °C), a mean field behavior of the susceptibility S(Q=0) was clearly observed, with a critical exponent γ=1. However, in a region of Tc−2.4 K≤T<Tc, a crossover occurs to a critical exponent γ≂1.26; it resembles the Ising behavior which is well established for normal liquid mixtures. The function S(Q) also describes the characteristic segmental length σ. Both σ and the range parameter of χ, r0, are i...

High-resolution focusing SANS with a toroidal neutron mirror

Presently, high-resolution instruments for small-angle neutron scattering (SANS) use the conventional pinhole cameras. For high resolution they have to be extremely long (80 m for D11). Much shorter instruments can be built with focusing mirrors [1–3]. So far, however, this principle was not successful because of the insufficient quality of conventional optical mirrors. Recently, we succeeded in building a 20 m long focusing instrument at the NSE spectrometer IN15 in the ILL Grenoble. It uses a 4 m long, high-quality mirror as developed for X-ray telescopes. The image has a sufficiently low parasitic halo. Test experiments on polymeric precipitates down to Q=4×10−4 A−1 were successfully carried out. We expect that the Q-range can be extended to ≈10−4 A−1.

Structural properties of native and sonicated cinerean, a β-(1 → 3)(1 → 6)-d-glucan produced by Botrytis cinerea

Cinerean, the extracellular beta-(1-->3) (1-->6)-D-glucan of the fungus Botrytis cinerea was studied. Electron micrographs of the native polysaccharide revealed quasi-endless fibrils with an estimated diameter of ca. 1.5 nm. A particle mass of 10(9)-10(10) daltons was determined from dilute solutions by low-angle laser light scattering. Sonication of increasing duration led to fragmentation of the native polymer with an approximately exponential decrease of mass in the range of average molecular masses between 250,000 and 50,000 daltons. Shadowed by platinum, cinerean fibril fragments with a weight-average molecular mass of 172,000 +/- 3000 daltons could be characterized from electron micrographs as a distribution of rods of most probable length of 45 nm and an average length of 72 nm. Small-angle X-ray scattering confirmed the fibrillar structure of the native cinerean and the rodlike structure of sonicated cinerean. A rod diameter of 1.9 +/- 0.2 nm and a mass per unit length of 2250 +/- 490 daltons/nm were found. The latter is in agreement with the value of 1830 daltons/nm calculated from the length distribution determined from the electron micrographs. These data-especially the mass per unit length-suggest a quaternary structure for the polysaccharide. Such a structure would explain the rigidity of the rods which, in turn, is responsible for the characteristic phase separation behaviour in aqueous solutions observed by nephelometry and viscometry.

Interface properties of blends of incompatible polymers

Abstract Neutron reflectometry is used to study the interface in blends of the partially compatible polymers deuterated polystyrene (PSd) and poly(styrene-co-4-bromo-styrene) (PB x S). The degree of bromination x controls the miscibility of the polymers. It is varied in a wide range in order to obtain information on the dependence of the interface width l on the compatibility of the components as expressed by the Flory Huggins interaction parameter χ. The kinetics of interface formation and the equilibrium values of l and χ as a function of bromination are discussed and compared to current theories.

Effect of the Onsager coefficient and internal relaxation modes on spinodal decomposition in the high molecular isotopic blend polystyrene/deutero‐polystyrene studied with small angle neutron scattering

The early state of spinodal decomposition was studied by small angle neutron scattering in the critical mixture of the isotopic blend deutero‐polystyrene/polystyrene (d‐PS/PS) of equal molecular volume of 1.42×106 cm3/mol in a temperature range 12 K≤‖Tc−T‖≤82 K. This process can be described by the relaxation between two static structure factors, S(Q) representing the equilibrium values of the system in the mixed state and at the temperature where phase separation occurs. The time evolution of the relaxation process is described by the dynamical structure factor, L(Q,t) which depends on the dynamic properties of the mixture. It will be shown that the static structure factor of a mixed system can also be determined in the unstable two‐phase region during the early state of spinodal decomposition. Consistent values for the Flory–Huggins parameter were found in comparison with a lower molecular d‐PS/PS sample and, therefore, a lower critical temperature which was even smaller than the phase separation temper...

SURFACE ENRICHMENT IN BLENDS OF MISCIBLE POLYMERS

Abstract The surface in binary blends of the partially miscible polymers deuterated polystyrene and poly(styrene-co-4-bromostyrene) with 6% brominated monomer units and various bulk compositions was studied by neutron reflection. Both the time-dependent and equilibrium properties of the blend are discussed. It is found that density profiles predicted by mean field theory are suitable to fit the experimental data. A depletion layer is established in the near surface region before equilibrium is reached. Properties like the Flory—Huggins interaction parameter χ and the diffusion coefficient D are calculated and compared with recent experimental results.

Interface Formation and Thin Film Properties of an Incompatible Polymer System

The polymer blend system of deuterated polystyrene (PS d ) and the statistical copolymer poly(styrene- co -para-bromo-styrene) (PBr x S) is partially compatible or incompatible depending on the degree of bromination x. The width of the interface in a bilayer system can thus be controlled in a wide range by an adjustment of x. This is demonstrated in neutron reflectivity experiments where the interfacial width is measured with an accuracy better than lnm. The interface width depends strongly on compatibility as expressed by the Flory-Huggins interaction parameter x- Results are compared with current theories.

Diffuse neutron scattering study of the short-range order in VD0.781

Abstract The short-range order of the deuterium atoms in a single crystal of disordered α-VD 0.781 was investigated by diffuse neutron scattering. The D—D pair correlations were analysed in terms of short-range-order parameters. From these results the D—D interaction parameters for a metal hydrogen system were determined for the first time by using the inverse Monte Carlo method.