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The interface between polystyrene and poly(methy1 methacrylate) homopolymers was investigated as a function of the concentration of added symmetric diblock copolymer of PS and PMMA, denoted P(S-b-MMA), using neutron reflectivity. It was found that as the number of P(S-b-MMA) chains added to the interface between PS and PMMA was increased, the width of the gradient between the PS and PMMA segments broadened. In particular, the width of the interface between PS and PMMA homopolymers is 50 A and, with the addition of P(S-b-MMA), increases to -85 A. At an amount corresponding to approximately half the thickness of the lamellar microdomain periodicity in the bulk, the interface becomes saturated with the copolymer. Further addition of copolymer chains to the interface results in a marked increase in the off-specular scattering, which is associated with either an ordering of the copolymer chains at the interface or an increase in the curvature of the interface. Studies were also performed on mixtures of homopolymers and copolymers. Here, the interface between the lamellar microdomains of the P(S-b-MMA) is found to increase from 50 A for the pure copolymer to 75 8, as PS and PMMA homopolymer is added to the copolymer. The broadening of the interface seen in both sets of experiments is due to a significant penetration of the homopolymer into the interfacial region. These results are consistent with the reduction in the interfacial tension between the homopolymers with the addition of the diblock copolymer.

Recent studies of molecular orientation in sheared liquid crystalline polymers have often yielded contradictory results. To check the self-consistency of methods for quantitative measurements of molecular orientation, liquid crystalline solutions of (hydroxypropyl)cellulose [HPC] and poly(benzyl glutamate) [PBG] have been studied using flow birefringence, X-ray scattering, and neutron scattering. HPC X-ray scattering patterns show an arclike pattern with a distinct peak as a function of scattering vector, while PBG patterns show a more diffuse equitorial streak. These differences are attributed to more strongly correlated lateral packing in HPC solutions due to their higher concentration. Measurements of orientation in steady shear flow agree well among the three techniques. Lyotropic HPC and PBG solutions differ in orientation at low shear rates. HPC solutions exhibit near zero orientation at low rates, while X-ray and neutron scattering measurements confirm previous birefringence data showing a low shear rate plateau of moderate orientation in PBG. Differences with recent neutron scattering measurements on PBG solutions that show low orientation at low shear rate are attributed to choice of solvent, rather than choice of technique. X-ray and optical data are consistent in showing decreasing orientation in HPC solutions during relaxation, but discrepancies are found in relaxation of PBG solutions. Large increases in flow birefringence suggest substantial orientation enhancement. X-ray data on one PBG solution confirm increasing orientation, but X-ray and neutron scattering data on a more concentrated solution show only modest changes in orientation. It is suggested that flow birefringence fails in this case due to texture coarsening to the point where there is no longer effective averaging over the distribution of director orientations along the light path.

of the oscillations in real space is somewhat longer on the trailing edge than on the leading edge. Therefore, interference effects are only observable when the two wave packets are nearly coincident as discussed by Klein, Opat, and Hamilton. 10 To our knowledge, this is the first experiment in which the detailed longitudinal shape of a neutron wave packet has been observed, and the uncertainty relation for neutrons in the longitudinal direction explicitly verified.

Stöber silica particles are used in a diverse range of applications. Despite their widespread industrial and scientific uses, information on the internal structure of the particles is non-trivial to obtain and is not often reported. In this work we have used spin-echo small angle neutron scattering (SESANS) in conjunction with ultra small angle X-ray scattering (USAXS) and pycnometry to study an aqueous dispersion of Stöber particles. Our results are in agreement with models which propose that Stöber particles have a porous core, with a significant fraction of the pores inaccessible to solvent. For samples prepared from the same master sample in a range of H2O : D2O ratio solutions we were able to model the SESANS results for the solution series assuming monodisperse, smooth surfaced spheres of radius 83 nm with an internal open pore volume fraction of 32% and a closed pore fraction of 10%. Our results are consistent with USAXS measurements. The protocol developed and discussed here shows that the SESANS technique is a powerful way to investigate particles much larger than those studied using conventional small angle scattering methods.

A magnetic Wollaston prism can spatially split a polarized neutron beam into two beams with different neutron spin states, in a manner analogous to an optical Wollaston prism. Such a Wollaston prism can be used to encode the trajectory of neutrons into the Larmor phase associated with their spin degree of freedom. This encoding can be used for neutron phase-contrast radiography and in spin echo scattering angle measurement (SESAME). In this paper, we show that magnetic Wollaston prisms with highly uniform magnetic fields and low Larmor phase aberration can be constructed to preserve neutron polarization using high temperature superconducting (HTS) materials. The Meissner effect of HTS films is used to confine magnetic fields produced electromagnetically by current-carrying HTS tape wound on suitably shaped soft iron pole pieces. The device is cooled to ~30 K by a closed cycle refrigerator, eliminating the need to replenish liquid cryogens and greatly simplifying operation and maintenance. A HTS film ensures that the magnetic field transition within the prism is sharp, well-defined, and planar due to the Meissner effect. The spin transport efficiency across the device was measured to be ~98.5% independent of neutron wavelength and energizing current. The position-dependent Larmor phase of neutron spins was measured at the NIST Center for Neutron Research facility and found to agree well with detailed simulations. The phase varies linearly with horizontal position, as required, and the neutron beam shows little depolarization. Consequently, the device has advantages over existing devices with similar functionality and provides the capability for a large neutron beam (20 mm × 30 mm) and an increase in length scales accessible to SESAME to beyond 10 μm. With further improvements of the external coupling guide field in the prototype device, a larger neutron beam could be employed.

We report an experiment demonstrating diffraction of cold neutrons by surface acoustic waves. We show that, in contrast to analogous experiments with light, the motion of the surface-acoustic-wave deformation of the surface requires significant modification of the diffraction equation applicable to stationary gratings. Diffracted beam intensities are in reasonable agreement with a simple theoretical treatment.PACS numbers: 61.12.Ex, 43.20.+g, The diffraction of light by the moving "grating" formed by a surface acoustic wave (SAW) is a wellknown phenomenon,^ which has been routinely used to investigate SAW propagation and attenuation characteristics.^ We report here an experiment which demonstrates the neutron-optical analogy of this effect.There are two main differences between the scattering of neutrons and the scattering of light by surface acoustic waves. Firstly, the refractive index ^ of matter for neutrons is very close to unity, i.e., for neutrons 1-//~10~^, whereas for light ^ -1 -1. This fact necessitates the use of grazing incidence for neutron investigations of surface phenomena. Secondly, for light, the SAW may be treated as a stationary grating to a very good approximation, while for neutrons this is not the case since the neutron speeds are an order of magnitude smaller than the SAW speed. We deal with this problem by transforming from the frame in which the SAW is stationary. An important consequence of this rapid motion of the grating is that the diffraction angles are much larger than those for neutrons diffracted by a stationary grating of the same spatial periodicity as the surface acoustic wavelength."*"^ Kinematics. -Consider a SAW propagating along the X axis on the surface of the material which occupies the space j; < 0. In the primed frame in which the SAW is stationary the diffraction-grating equation for reflected neutrons incident in the A'-K plane may be writtenwhere k' is the neutron wave number, 0' the glancing angle of incidence, and 9'n the angle of the nth diffracted beam (n =0, ± 1, ± 2, . . . ). ^ is the SAW wave number, and the integer ^ is ± 1 depending on whether the propagation of the SAW and the incident neutrons have the same or opposite senses. A Galilean transformation from the stationary to the (unprimed) laboratory frame yields the resultwhere K = mu/h, m is the neutron mass, and u is the SAW speed. The second of these equations corresponds to a neutron energy change due to the absorption of n phonons, and the diffracted-beam neutron wave number is consequently subscripted. For our experiment K<^{k,K) and (0,^")<^1, which yields the approximation el-0^^2n{K/k)[K/k-s].(3)The factor K/k-s is the ratio of the SAW velocity in the neutron rest frame to the neutron velocity in the laboratory. For cold neutrons this factor is an order of magnitude greater than unity, its value for a stationary grating of the same spatial frequency, and results in a significant enhancement of the diffraction angles.Dynamics. -In the stationary SAW frame, the relevant Schrodinger equation is dx...

We describe the design and operation of a temperature controlled Couette shear cell for small angle neutron scattering ͑SANS͒ studies of complex fluids under flow. This design incorporates a vapor barrier, which prevents sample evaporation to relatively high shear rates. This cell enables the investigation of systems which are highly sensitive to evaporation. Over the duration of a Couette SANS measurement composition phase transitions due to evaporation can be misinterpreted as true shear-induced transformations. We give a brief report of recent experiments performed on one such system: bicontinuous L 3 sponge phases for which the surfactant membrane constituents are Cetylpyridinium chloride and hexanol. These clearly demonstrate the limitations of previous designs and the utility of the vapor barrier in measurements of a predicted shear induced sponge to lamellar phase transition. Using this cell we also describe and test a simple and effective way to put SANS data taken in the tangential Couette configuration on an absolute scale.