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Blending (or mixing) of macromolecules is widely used to tailor the properties of polymeric materials and small-angle neutron scattering (SANS) has provided detailed information at the molecular level on the ability of different polymer species to mix or segregate at various thermodynamic conditions. For two decades, SANS data have been analyzed via the de Gennes “random phase approximation” (RPA) [P.-G. de Gennes, Scaling Concepts in Polymer Physics, second ed., Cornell University Press, Ithaca, London, 1979], which is based on the assumption that the dimensions of polymer chains remain unchanged on mixing for all concentrations and temperatures. Here we investigate the effect of temperature and concentration on the dimensions of macromolecules in blends using SANS and high-concentration labeling methods and construct a generic phase diagram, which specifies the range of validity of the RPA. Using scaling arguments, we demonstrate a parallel between the structure–property relationships in blends and solutions of polymers in small molecule solvents and reveal the impact of the chain length of the polymeric solvent on the phase behavior of polymer blends. The results offer new insights into the universality of the thermodynamic properties and structure of macromolecules in polymeric, liquid and supercritical solvents.

We study a product pricing model in social networks where the value a possible buyer (vertex) assigns to a product is influenced by the previous buyers and buying proceeds in discrete, synchronous rounds. Each arc in the social network is weighted with the amount by which the value that the end node of the arc assigns to the product is changed in the following rounds when the starting node buys the product. We show that computing the price generating the maximum revenue for the product seller in this setting is possible in strongly polynomial time if all arc weights are non-negative, but the problem becomes NP-hard when negative arc weights are allowed. Moreover, we show that the optimization version of the problem exhibits the interesting property that it is solvable in pseudopolynomial time but not approximable within any constant factor unless P = NP.

An ethylene-hexene copolymer, representative of many heterogeneous linear low-density polyethylenes (LLDPEs), has been shown to contain a dispersed minority phase (volume fraction similar to 10(-2).), which was manifested by departures from a Q(-2) variation of the neutron scattering cross section at low Q values. After xylene extraction, which removes the highly branched amorphous material, the dispersed phase is removed to a good approximation. In contrast, a metallocene-based LLDPE, which has a more homogeneous distribution of branch contents, does not exhibit an upturn in the cross section in the limit of low momentum transfer (Q < 10(-2) Angstrom (-1)), indicating that the LLDPE forms only a single phase in the melt. The composition variance is calculated from the comonomer composition distribution obtained by temperature-rising elution fractionation (TREF) and used to estimate proximity of the melts to the spinodal condition. These findings support previous conclusions for compositionally polydisperse LLDPEs, whereby the highly branched molecules in the distribution may phase segregate, even if the overall branch content is low. When this component is not present, as in metallocene-based LLDPEs, the system forms a single phase in the melt.

A new two-dimensional position-sensitive detector system for small-angle neutron scattering experiments is under development. It is based on a 60/spl times/60 cm/sup 2/ large /sup 6/Li-glass scintillator for the neutron capture and dispersion of the emitted light on an array of photomultiplier tubes for the derivation of the event position. For subthermal neutrons of 8 /spl Aring/, an efficiency of 96% and a spatial resolution of 8 mm are to be achieved. Major improvements have been made in the signal- and data-processing branch, which aims at an electronic dead time of 1 /spl mu/s. A fast digitalization method using free-running analog-to-digital converters for each photomultiplier combined with field-programmable gate arrays for a parallel event detection in all channels has been applied. A subsequent farm of up to 16 floating-point digital signal processors is used to provide enough computing power for an improved reconstruction of the event position according to a maximum likelihood method.

By means of small-angle neutron-scattering (SANS) experiments, the dependence on concentration and temperature of the mean aggregation number 〈N〉 of rodlike tetradecyldimethylaminoxide (TDMAO) micelles in D2O was determined for 278 K < T < 370 K and for 2.69 mM/L < c < 118 mM/L. By an analysis via the so-called ladder model, the difference of the chemical potentials for a monomer located in the end cap and one in the cylindrical part of the spherocylindrical micelles, respectively, was extracted. This difference depends on the concentration c of TDMAO and strongly on temperature T.

Neutron diffraction from charge stabilized shear ordered colloidal dispersions at rest and under sheared conditions are presented. A newly designed shear cell is used to generate a linear shear profile. Hexagonal scattering patterns were observed both at rest and under sheared conditions. The stacking probability A is determined by measuring the intensity dependence of the Bragg spots as a function of the angle between the incoming neutron beam and the sample cell. The shear experiments are discussed in terms of a continuous distortion [W. Loose and B. J. Ackerson, J. Chem. Phys. 101, 7211 (1994)] at small shear rates, and shear melting at higher shear rates.

Thermal composition fluctuations in a homogeneous binary polymer blend and in a diblock copolymer were measured by small-angle neutron scattering as a function of temperature and pressure. The experimental data were analyzed with theoretical expressions, including the important effect of thermal fluctuations. Phase boundaries, the Flory–Huggins interaction parameter and the Ginzburg number were obtained. The packing of the molecules changes with pressure. Therefore, the degree of thermal fluctuation as a function of packing and temperature was studied. While in polymer blends packing leads, in some respects, to a universal behaviour, such behaviour is not found in diblock copolymers. It is shown that the Ginzburg number decreases with pressure sensitively in blends, while it is constant in diblock copolymers. The Ginzburg number is an estimation of the transition between the universality classes of the `mean-field' approximation and the three-dimensional Ising model. The phase boundaries in blends increase with pressure, while the phase boundary of the studied block copolymer shows an unusual shape: with increasing pressure it first decreases and then increases. Its origin is an increase of the entropic and of the enthalpic parts, respectively, of the Flory–Huggins interaction parameter.

The effect of concentration of silica particles in hydrogenated solutions on the small-angle neutron scattering was investigated in the scattering vector range between 6.3 × 103 and 3.5 × 10−1 aA−1. The samples were prepared with volume concentrations from 0.3 up to 16.3%. The experimental data show interference of the scattered neutrons, whose peak shifts towards higher Q values with increasing concentration. The form factor of the silica particle population was determined and, from this, the structure factor was extracted, from which the effective reduced pair correlation functions for the silica particles could be evaluated. Ordering effects of silica particles at various concentration were studied in hydrogenated solutions by SANS.

Quasielastic neutron scattering has been used to study the motion of protons in two solutions of poly(γ-benzyl L-glutamate) (PBLG) and deuterated benzyl alcohol (DBA) as they are brought from the high temperature (cholesteric and isotropic) phase towards the gel. Quasielastic neutron scattering results demonstrate that, in both the isotropic and cholesteric phases, the local rotational dynamics of the polymer are continuous in the high temperature phases, but become more constrained as the system approaches and enters the gel phase. The results also show that the energetics of the rotational motion of the protons below the gelation threshold are independent of the initial phase and the protons are not rendered immobile in the gel phase. © 1996 John Wiley & Sons, Inc.

Small-angle neutron scattering has been used to study poly(γ-benzyl L-glutamate) (PBLG) in deuterated benzyl alcohol (DBA) as the solution is brought from the isotropic phase into the gel phase. The results show that an aggregation of PBLG molecules exists up to 80°C even in the isotropic phase and the size of the aggregate does not change with temperature within the isotropic phase for a given concentration. However, the size of the aggregate increases with concentration or as the gelation threshold is crossed. The measurement of fractal dimension at intermediate length scales of the aggregates in the isotropic phase shows that the aggregates are less dense at higher polymer concentrations. But at lower length scales of ∼50 A, the mesh size of the aggregates in the isotropic phase decreases with increasing polymer concentration. Studies of the fractal dimension of the resultant gels show that the thermal history of the sample in the isotropic phase influences the gel microstructure. The fractal dimension of the PBLG-DBA gel obtained by a step quench procedure is higher than that of a gel obtained by a sudden quench. We have also observed that the local concentration gradients become sharper as the polymer concentration increases in the gel phase.

This report deals with SANS experiments for the investigation of polymer blends, referring to our high pressure, and to time-resolved work. The experiments were started in the ELLA (cold neutron) laboratory installed in the KFA Julich research reactor FRJ-2. Since the FRJ-2 reactor operation was interrupted by technical problems from autumn 1990 until now, the work has continued on other neutron sources, essentially at the SANS instruments at the Ris⊘ Research Center and at GKSS Geesthacht. Consequently, part of the presented data (see Figure 3 and Figure 6) was obtained at these instruments (which are quite similar to ours) and not at the FRJ-2. In spite of this problem, we take the opportunity to present a general and brief description of our FRJ-2 cold neutron instrumentation, mainly in small angle scattering, in a separate chapter of the article.

This article presents recent results of a small angle neutron scattering (SANS) study of modified martensitic steel DIN 1.4914 (MANET), subject to implantation with α-particles and to subsequent isochronal annealings at 798, 948, 1098 and 1248 K. The analysis of the SANS nuclear cross sections related to the presence of He bubbles gives quantitative microstructural parameters of the bubble population for the different temperatures and provides information on the gas pressure within the bubbles.

The growth of helium bubbles in irradiated MANET steel was studied by using the small angle neutron scattering (SANS) and the transmission electron microscopy (TEM) techniques. Good agreement was found for the values of the considered microstructural quantities. Contrary to simpler model systems no overpressure of the gas inside the bubbles was found in this complex steel.

A 100 μm thick specimen of Fe-15% Cr-15% Ni (serving as a model alloy for austenitic stainless steels) has been homogeneously implanted with 1200 appm He and then isothermally annealed at 973 K for periods between 0.25 and 2780 h. After each annealing step the size distribution and the density of helium bubbles have been determined by small angle neutron scattering (SANS). After the last annealing step the bubble structure was also measured by TEM and good agreement with SANS results was found. The observed changes of the mean bubble radius and the bubble density with annealing time can be described by power laws. The corresponding exponents of 0.14 and −0.37, respectively, indicate bubble migration and coalescence as the dominating coarsening mechanism. It is further concluded that the gas pressure in the bubbles is significantly higher than the thermal equilibrium value, in agreement with earlier results on pure nickel.

Neutron radiation offers significant advantages for the study of biological molecular structure and dynamics. A broad and significant effort towards instrumental and methodological development to facilitate biology experiments at neutron sources worldwide is reviewed.

Neutron small angle scattering (SANS) combined with transmission electron microscopy (TEM) has been applied to obtain detailed information on the bubble structure in Ni, implanted with 1200 appm helium at room temperature and annealed at temperatures up to 1173 K. Besides conventional information such as size distributions of “small” bubbles in the bulk and “large” bubbles near grain boundaries, the density of helium in the bubbles could directly be determined by a contrast variation method of SANS. The most important result is the finding that even after the highest annealing temperature of 1173 K (≈ 70% of the melting temperature), the bubbles contain an overpressure which lies about 3 GPa above the value for thermodynamic equilibrium.

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.

The morphology of particles in the isotropic phases of mixed aqueous colloids of lecithin and glycocholate are studied using small-angle neutron scattering. At the highest concentrations globular mixed micelles are present and have a radius of gyration of 24 A. At lower concentrations rod-like structures are present. In each and every case the rod radii are about 27 A. It is proposed that the rods form by aggregation of disk-like micelles about 27 A radius and height 50 A. The rods grow larger as the solutions are diluted and appear to associate into loose networks just before the occurrence of a concentration-induced transition to vesicles. The vesicles have walls that are a single lipid bilayer of lecithin and glycocholate.

With neutron small-angle scattering it was found, for two different polymer blends, that the time-dependent structure factor S(Q, t) relaxes exponentially or also non-exponentially after a temperature step has been applied. The classical Cahn-Hilliard-Cook theory predicts an exponential time behaviour of S(Q, t). The observed deviations may be due to the correlation of the order parameter with internal motions of the polymer segments or with other internal variables of a viscoelastic material near its glass transition.

During the upgrade of the small-angle neutron scattering instrument KWS-1 at the research reactor FRJ-2, the 15-yr-old detector system has been replaced. While the Anger camera-based concept of the detector remained unchanged, the signal and data processing branch has been completely revised. Because of higher count rate requirements, a highly configurable parallel readout electronics has been developed aiming at counting rates of several hundred kilohertz. The whole detector system has been recently installed at KWS-1 and measurements to study the system performance have been carried out. The linearity and spatial resolution of the new detector have been determined by an analysis of an acquired image taken with a hole diaphragm in front of the scintillator. The overall system dead time has been measured by comparing the detector count rates at several scattering intensities to the count rates achieved with a fission chamber. Finally, scattering patterns of well-known samples have been taken in order to demonstrate the quality of the acquired images.

In mouse mammary tumorigenesis, p53 mutations facilitate tumorigenesis in concert with other oncogenic alterations. Ionizing radiation enhances tumorigenesis in preneoplastic mammary outgrowth lines and induces p53-dependent apoptosis. We asked if normal p53 function modulates radiation-induced tumorigenesis in preneoplastic mammary lesions by affecting the apoptotic pathway of cell deletion. Three different hyperplastic outgrowth lines were compared. Outgrowth line D1 overexpressed wild-type p53 and responded to irradiation with enhanced tumorigenicity but no induction of apoptosis. Outgrowth line TM12 exhibited normal wild-type p53 expression and responded to irradiation with no alteration in tumorigenicity but with a marked increase in apoptosis. Outgrowth line TM2L also exhibited normal wild-type p53 expression and responded to irradiation with a marked enhancement in both tumorigenicity and apoptosis. These results indicate that the two radiation-induced responses, apoptosis and tumorigenesis, are dissociable events in the mammary gland. Furthermore, radiation-induced tumorigenicity was not abrogated by either enhanced wild-type p53 expression or a robust apoptotic response. The radiation dose of 5 Gy most likely induces multiple genetic alterations in surviving cells, including genomic instability, and this may account for the tumorigenicity. Future experiments will examine lower doses of irradiation that still induce a significant apoptotic response but significantly less genomic instability.

An overview of contrast variation in SANS with polarized neutrons and targets is given. Examples from metal physics and biology demonstrate the advantages and the gain of information by this technique.

Small angle neutron scattering (SANS) studies in combination with transmission electron microscopy (TEM) were performed on the cast nickel base superalloy Alloy 713 LC and on a Hf-modified version of the same alloy. With the aid of the TEM results the profile of the scattering curves was correlated with the M23C6 carbide and the γ′ precipitates. A coarsening of the γ′ precipitates with increasing creep deformation to a larger plate-like shape was observed. The small axis of these precipitates averaged over the grains was parallel to the stress axis. The γ′precipitates start to become anisotropic even in the primary stage of creep. In the vicinity of the fracture surface the volume fraction of the cavities and microcracks caused by creep deformation was 10−3 to 10−2 The influence of the cavities was indicated by the smaller anisotropy factor measured near the fracture surface in comparison to the rest of the cylindrical part of the specimen. The variation of the anisotropy factor as determined by the SANS-method may be used to nondestructively measure the accumulated damage in the material.

Small angle neutron scattering experiments are carried out with an isobutyric acid (COOD)/deuterium oxide mixture of critical composition. The scattering patterns are measured at small temperature differences (T - Tc) ≦ 1.0 K above the critical temperature Tc. In his temperature range and for scattering vectors larger than 0.03 A−1 the critical scattering was found to be independent of temperaure. From these data the experimental correlation scaling function gexp(x) is constructed for values of the scaling variable x in the range 4 < x < 540. The Fisher-Langer approximation of the correlation scaling function and its asymptotic form for large values of x are fitted to gexp(x). In this way a value of the critical exponent η of η = 0.039 ± 0.009 is obtained. It is based on the analysis of the experimental correlation scaling function composed of five scattering patterns obtained at five different temperature differences (ΔT ≤ 1.0 K). The analysis of 4 individual scattering patterns (ΔT ≤ 0.08 K) gives η = 0.037 ± 0.006.

The coherent composition fluctuation in the system Al-Zn was measured by neutron small angle scattering in the temperature range between 435 and 324°C. No critical scattering could be detected at the incoherent critical point (Tinc = 357.5°C). The intensity of the scattered neutrons increases continuously when the temperature decreases from 435 to 324°C. The scattering curves below T = 324°C differ from the others essentially by their high intensity for small κ- and their sharper decrease with increasing κ-values. These results agree with Cahn's theory which predicts a decrease of the critical point due to the elastic energy built up by composition fluctuation. The measured shift of ΔT = 28° is in good agreement with the theoretical estimate. The strong increase of intensity below T = 324°C is due to the rapid decomposition behaviour in the unstable state of the system.

Decomposition of a polymer blend in the miscibility gap has been studied by small angle scattering of neutrons, using a double crystal diffractometer. It covers a range of 10−5 to 10−3 A−1, which connects the region of elastic light scattering and, at the upper end, the region of conventional neutron small angle scattering instruments. The decomposed structure in the miscibility gap can be described by a characteristic lengthR which increases with time,t1/3 between 7 and 25 min. At longer times, the growth follows a more linear power law. This behaviour is consistent with predictions of the domain growth for liquid mixtures and is estimated by using the self diffusion constant, viscosity, and the surface energy of the polymer.

Magnetic small-angle scattering of neutrons by dislocations has been investigated in a plastically deformed nickel single crystal between 300 and 540K. By proper adjustment of the magnetic field strength the range of magnetic disturbance around dislocation lines, i.e. the magnetic exchange length, could be held fixed at 16.5 nm for all temperatures. The experimental results are compared to calculations based on micromagnetic theory.

The energy shift due to the inelastic interaction of the neutron with the time dependent magnetic fields of a gradient radio-frequency spin flipper was studied. A nondispersive perfect crystal spectrometer was used to measure extremly small energy changes of ΔE∼0.2 μeV. The gradient of the magnetic field causes a broadband action of the spin flipper which facilitates its use for new active neutron optical components.

Neutron-diffraction studies of the null matrix $^{62}\mathrm{Ni}$-41.4-at.%-$^{65}\mathrm{Cu}$ have been performed after thermal treatment and after irradiation with 3-MeV electrons at temperatures between 373 and 510 K. The diffuse neutron scattering has been measured to determine the Warren-Cowley short-range-order parameters and additionally the neutron small-angle scattering has been investigated for detecting any possible decomposition or segregation in the Ni-Cu alloy. In the special case of Ni-Cu alloys the experiments demonstrate the successful combination of electron-irradiation and neutron-diffraction measurement, two experimental procedures with normally contradictory requirements. As a result of the diffuse scattering a significant increase of the atomic short-range clustering under irradiation has been observed, corroborating the interpretation of previous electrical-resistivity and magnetic-susceptibility measurements. In small-angle scattering the formation of periodic concentration fluctuations is observed as it is expected for spinodal decomposition, giving the first experimental evidence of the suggested miscibility gap in Ni-Cu.

Ferromagnetic single-domain cobalt precipitates have been produced in single-crystal copper spheres with about 1% cobalt by annealing between 5 and 40 hours at 873 K in a magnetic field of 1·5 × 106 Am−1 applied parallel to the [100] direction. Small-angle neutron diffraction studies have been performed on these specimens in the (100) and (0&1bar;1) planes. The size and geometrical shape of the cobalt particles have been found to confirm an earlier assumption; the particles are of octahedral shape with a few per cent deviation from sphericity and with some additional 3% elongation in the direction of the magnetic field which was applied during annealing. Contrary to earlier assumptions, particles annealed in a field parallel to 〈100〉 are not prolate ellipsoids. The deviation of particle shape from sphericity was found to be almost independent of annealing time. Moreover we have observed a pronounced short-range order between the precipitates which could not be deduced from earlier experiments. Th...

The composition of GPI zones in Al Cu (fraction α of copper in a zone and number n of layers in a platelet) and the fraction X of copper precipitated into zones are still controversial. We have performed small angle neutron scattering from GPI zones in polycrystalline alloys with 1 and 1.85 at.% Cu which were aged at 22 and 100°C. The GPI zones are described by a dislocation loop model with the product Xαn , the zone radius R and the Burgers vector of the loops as free parameters. It turned out that Xαn , depends strongly on the copper concentration c 0 and on the ageing temperature T A . Xαn , and also Xα are always substantially smaller than 1. The radius of the zones is also dependent on c 0 and T a The largest observed radii of GPI zones were 1.6nm.

The density of helium in bubbles produced in two Ni isotopes by α-implantation and isochronal annealing has been measured by the contrast variation method of SANS. A further evaluation of the SANS data after the last annealing step at 1123 K yielded a bimodal size distribution. Assuming equilibrium bubbles a consistent set of parameters characterizing the bubble populations could be extracted from the scattering data. Those parameters for the “small” and “large” bubbles are: The atomic He densities are 0.7 and 0.17 of the atomic Ni density, the mean radii are 1.2 and 13 nm, the volume fractions are 0.011 and 0.0074 and the He contents are 790 appm and 120 appm, respectively. The values for the “small” bubbles are in good agreement with the TEM results. However, the existence of “large” bubbles could not be confirmed by TEM, probably because of a spatially inhomogeneous distribution.

High angular resolution neutron transmission measurements are proposed as a non-destructive materials testing method for diagnosing microstructure. The essential part of the instrument is a perfect monolithic silicon single crystal 30 cm long and 5 cm in diameter which has been cut away to leave two parallel ‘ears’ connected by the bottom part of the crystal. Cavitation voids with sizes up to 10μm can be sensitively detected. The experimental results from three different high temperature alloys are given, which illustrate the applicability of this instrument.

Diffuse scattering of thermal neutrons was used to investigate the kinetics of clustering in Cu-Ni alloys. In order to optimize the experimental conditions the isotopes 6SC~ and 62Ni were alloyed. The time evolution of the diffuse scattered intensity at 400 oC has been measured for eight Cu-Ni alloys, varying in composition between 30 and 80 at. % Ni. The relaxation of the so called null matrix. containing 56.5 at. O/, Ni, has also been investigated at 320, 340, 425 and 450 OC. Using Cook's model from all these measurements information has been deduced about diffusion at low temperatures and about thermodynamic properties of the Cu-Ni system. It turns out that Cook's model is not sufficiently detailed for an accurate description of the initial stages of these relaxations. Introduction. - The kinetics of clustering and short range order (s.r.0.) in stable solid solutions were discussed from a theoretical point of view by Cook (I). His model is based on the lattice diffusion theory for spinodal decomposition as developed by Cook, De Fontaine and Hilliard 123. The model gave good agreement with data on the kinetics of s.r.0. as measured by one of the authors (3,4). At that time no experimental data on clustering were available. One of the important results of Cook's theory was that he demonstrated the impossibility of describing cluster- ing kinetics, even approximately, by a single relaxation time in contrast to short-range order kinetics. Important theoretical contributions have been given by Khachaturyan (5) and Yamauchi (6), but in this paper we will mainly limit ourselves to a comparison with Cook's theory. For binary alloys he derived the following expres

Channel-cut crystals have been tested to reduce the tails of double crystal rocking curves. Such devices are useful tools for small angle scattering experiments in the Q -range between 10 −5 and 10 −3 A −1 and for real time experiments at short time scales. Therefore, large objects and large distance interparticle correlations can be investigated advantageously by this method. Test measurements with Latex sphere, polymer blends and lamellar structures have shown the capacity of perfect crystal small angle scattering cameras. The radius of gyration and the characteristic dimension of the lamellar structure have been determined.

The method of SANS was applied to study critical fluctuations and precipitates in blends of large molecules. The critical behaviour has been investigated for an oligomer blend: n-hexane/n-perfluorohexane; furthermore, for a blend with high molecular weight, PVME/d-PS, the growth of precipitates was measured by means of a double crystal diffractometer with a resolution of 10 -5 A -1 .

This paper is a study by neutron small angle scattering of the polymer blend* polyvenylmethy1ether and deuterated polystyrene. The blend is a compatible system with a miscibility gap at high temperature, and a lower critical solution temperature (LCST). The aim of the Investigations was primarily a study of the time dependent structure factor S(Q,t) for neutron small angle scattering in the unstable region. This was achieved by means of a double crystal diffractometer (DKD). Its resolution of the scattering vector Q is of the order of 5 • 10-5A-1 The dynamics of precipitates — the early states and the regime of coarsening — are easily accessible because the growth rates are small and can be easily resolved. Furthermore, the early stages can be treated by theory in the meanfield approximation1.

A general discussion of the gas density determination of He bubbles in Ni and Fe with neutron scattering using the contrast variation method is given. One finds, that best results are obtained using isotope combinations for Ni, and magnetic and nuclear scattering for Fe. An experiment to determine the density of He in Ni demonstrates the applicability of this method.

The article deals with the phase diagram and spinodal decomposition of two polymers blends, namely d—PS/PVME and d(deutero)—PS/PS, investigated by small angle neutron scattering (SANS). The result of the static experiments is the excess free energy and the phase diagram. This is used as a basis for studies of non—equilibrium phenomena as spinodal decomposition. In polymer blends the Cahn—Hilliard—Cook theory of the early state of spinodal decomposition can be tested easily, because the blends have rather low relaxation rates; and they are meanfield systems [2,6] which makes interpretation simple, except in a very narrow temperature region near the critical point [6]. The kinetics in the isotopic blend d—PS/PS are so slow that the early states of spinodal decomposition can be studied within minutes. The presented SANS results have been performed at the KWS I small angle instrument at the FRJ—2 reactor in the KFA Jülich.