We present small angle neutron scattering measurements of the static structure factor S(q) of the binary fluid mixture water-lutidine imbibed into the porous glass Vycor as a function of temperature and composition. S(q) changes from a Lorentzian in the one phase region to a Lorentzian squared at the random field transition. The correlation length increases from ∼ 20 A in the one phase region to to ∼ 52 Å (≈ pore diameter) in the frozen domain state.

We present small angle neutron scattering data of porous glasses. Analysis of the structure factor shows that the morphology on length scales between 30 A and 800 A depends on fabrication procedures. Fast gelation leads to a clumpy glass, whereas slow gelation produces a random smooth internal interface.

Uranium silicides have been considered for use as reactor fuels in both high power and low enrichment applications. However, U3 Si was found to become amorphous under irradiation [1] and to become mechanically unstable to rapid growth by plastic flow [2,3]. U3Si2 appears to be stable against amorphization at low displacement rates, but the extent of this stability is uncertain. Although the mechanisms responsible for plastic flow in U3Si and other amorphous systems are unknown, as is the importance of crystal structure for amorphization, it may not be surprising that these materials amorphize, in light of the fact that many radioactive nuclide - containing minerals are known to metaminctize (lose crystallinity) under irradiation [4]. The present experiment follows the detailed changes in the crystal structures of U3Si and U3Si2 introduced by neutron bombardment and subsequent uranium fission at room temperature. U-Si seems the ideal system for a neutron diffraction investigation- since the crystallographic and amorphous forms can be studied simultaneously by combining conventional Rietveld refinement of the crystallographic phases with Fourier-filtering analysis [5] of the non-crystalline scattering component.

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.

We use small angle neutron scattering (SANS) to study the microstructure of porous Vycor glass and the capillary condensation of fluids in the medium. Using a chord distribution model, we can predict the structure factor measured by SANS. Excellent agreement with the data is obtained. The fitted parameters characterize quantitatively the porous structure before and during the process of condensation, and are in good agreement with isotherm measurements. However, at the latest stages of the process, when all the pores are nearly filled, the model can no longer describe the system.

We have studied star-branched polymers in solution under various labelling and contrast matching conditions by small angle neutron scattering and neutron spin echo spectroscopy. We have investigated the relation between the static and dynamic partial structure factors of the variously labeled star polymers. The system of interest is a set of solutions containing 12-arm star branched polyisoprene of arm-molecular weight of 8000, and two polystyrene 12-arm stars, one fully labelled, the other with one arm labelled. The polyisoprene star polymer arms consisted of diblock copolymers, half-deuterated, and half-protonated. Measurements were performed on a center-deuterated star in a contrasted matching deuterated solvent (shell contrast), and on a reverse labelled star with core contrast. We have also studied a solution with the solvent matched the average star scattering length density and solutions containing identical stars with protonated homopolymers. It is found that in the frame-work of the random phase approximations, the initial relaxation rate of the partial dynamic structure factors can be quantitatively accounted for by a function of the eigenmodes of the mobility matrix weighted by an appropriate combinations of the various partial static structure factors.

Deuterated polybutadiene and protonated polybutadiene (PBD/PBH) blends with various microstructures have been studied by the small-angle neutron scattering experiments. Correlation length, ξ, zero-wavenumber structure factor, S(q=o), and interaction parameter, Xblend have been obtained. All PBD/PBH blends exhibit UCST behavior. With the use of random copolymer theory, the interaction parameter, Xblend, has been successfully separated into X1, X2 and X3 which are interaction parameters between the same isotope labeled 1,2-unit and 1,4-unit, opposite isotope labeled 1,2-unit and 1,4- unit, and opposite isotope labeled 1,2-unit with 1,2-unit or 1,4-unit with 1,4-unit, respectively.

Neutron scattering measurements were conducted to investigate the conformation of the molecular networks in epoxies. Emphasis was placed on the changes in the scattering intensity resulting from curing. Experimental results on homopolymerized epoxy as well as a theoretical interpretation of the results are presented.

The phase behavior of polymer blends and solutions can be changed dramatically by a flow field using a variety of flow geometries. Unlike simple binary fluids which require extremely high shear rates to produce only small shifts in the phase boundary, polymer phase behavior may be influenced by as much as 10 degrees with the application of much lower shear rates. However, there is a large body of conflicting data concerning the nature of these shear effects in polymers.

Here we report on the effects of shear on the phase behavior of polymer blends by small angle neutron scattering (SANS). Experiments were conducted using a specially constructed, concentric cylinder apparatus for in situ studies of concentrated polymer solutions and melts. Two separate systems will be discussed: 1) a blend of polystyrene and polybutadiene. 2) a blend of polystyrene and poly(vinylmethylether). Both systems exhibit shifts in the phase behavior which indicate shear induced mixing in agreement with previous results obtained by other techniques. These results will be interpreted within the context of existing theories of shear induced phase behavior.

Neutron reflectivity has been used to determine the concentration profile at the vacuum-polymer interface for a two polymer blend. To quantify surface enrichment and evaporation due to differences in chain length, we have measured the reflectivity of a mixture of short deuterated and long protonated polystyrene chains (DPS & PS), with a weight fraction of 0.5. When a mixture of DPS and PS chains of molecular weight 720 and 910k respectively were annealed, a small but measurable increase in asymptotic reflectivity occured, coupled with a decrease of film thickness and scattering length density. This is indicative of surface enrichment and evaporation of the light chains (DPS). Ellipsometry studies confirmed that the short chains evaporated and its rate was established as a function of the temperature. Upon increasing the DPS molecular weight to 9600, the enrichment becomes considerably greater whilst the evaporation becomes negligible.