A software package is presented for performing reduction and analysis of smallangle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) data. A graphical interface has been developed to visualize and quickly reduce raw SANS and USANS data into one-or two-dimensional formats for interpretation. The resulting reduced data can then be analyzed using model-independent methods or non-linear fitting to one of a large and growing catalog of included structural models. The different instrumental smearing effects for slit-smeared USANS and pinhole-smeared SANS data are handled automatically during analysis. In addition, any number of SANS and USANS data sets can be analyzed simultaneously. The reduction operations and analysis models are written in a modular format for extensibility, allowing users to contribute code and models for distribution to all users. The software package is based on Igor Pro, providing freely distributable and modifiable code that runs on Macintosh and Windows operating systems.

Extensive visual and quantitative studies of turbulent boundary layers are described. Visual studies reveal the presence of surprisingly well-organized spatially and temporally dependent motions within the so-called ‘laminar sublayer’. These motions lead to the formation of low-speed streaks in the region very near the wall. The streaks interact with the outer portions of the flow through a process of gradual ‘lift-up’, then sudden oscillation, bursting, and ejection. It is felt that these processes play a dominant role in the production of new turbulence and the transport of turbulence within the boundary layer on smooth walls.Quantitative data are presented providing an association of the observed structure features with the accepted ‘regions’ of the boundary layer in non-dimensional co-ordinates; these data include zero, negative and positive pressure gradients on smooth walls. Instantaneous spanwise velocity profiles for the inner layers are given, and dimensionless correlations for mean streak-spacing and break-up frequency are presented.Tentative mechanisms for formation and break-up of the low-speed streaks are proposed, and other evidence regarding the implications and importance of the streak structure in turbulent boundary layers is reviewed.

The structure of the flat plate incompressible smooth-surface boundary layer in a low-speed water flow is examined using hydrogen-bubble measurements and also hot-wire measurements with dye visualization. Particular emphasis is placed on the details of the process of turbulence production near the wall. In the zone 0 < y+ < 100, the data show that essentially all turbulence production occurs during intermittent ‘bursting’ periods. ‘Bursts’ are described in some detail.The uncertainties in the bubble data are large, but they have the distinct advantage of providing velocity profiles as a function of time and the time sequences of events. These data show that the velocity profiles during bursting periods assume a shape which is qualitatively distinct from the well-known mean profiles. The observations are also used as the basis for a discussion of possible appropriate mathematical models for turbulence production.

The clustering phenomenon has been observed in many macromolecular systems. Poly-(ethylene oxide) solutions are characterized by a clustering effect that has been extensively discussed in the literature. Its origin has remained elusive. Using small-angle neutron scattering from PEO solutions in various deuterated solvents, the possible causes of clustering that have been given in the literature are analyzed here. These include impurities in water, possible PEO crystallization, a subtle phase transition whereby a concentrated phase coexists with free polymer coils, hydrogen-bond physical crosslinking, and finally chain ends effect. We have shown that under the experimental conditions considered here (4% PEO weight fraction) the mostly forgotten chain ends effect is at the origin of clustering in poly(ethylene oxide) solutions.

A structural description of liquid particle dispersions: Ultracentrifugation and small angle neutron scattering studies of microemulsionsWe have studied the phase behavior, wetting transitions, and small angle neutron scattering (SANS) of water, n-alkane, and n-alkyl polyglycol ether (C;E) systems in order to locate the transition between weakly structured mixtures and microemulsions, and to provide a measure for the transition. We first determined the wetting transition by macroscopic measurements and then measured the location of the Lifshitz lines by SANS. Starting with wel1-structured mixtures (exhibiting nonwetting middle phases and wel1-expressed scattering peaks, features that qualify them as microemulsions) the wetting transition was induced by increasing the chain length of the alkane or by changing the oil/water volume ratio, and then the Lifshitz line was crossed. Further, starting with systems past the disorder line (weakly structured mixtures that display wetting middle phases and no scattering peaks), local structure was induced by either increasing the surfactant concentration or decreasing the oil/water volume ratio or the temperature. In each case a Lifshitz line was crossed. Analyzing the scattering experiments quantitatively, allows determination of the amphiphilicity factor, which is a measure of the strength of the surfactant. The results suggest there is a sequence of roughly parallel surfaces within the three-dimensional composition-temperature space. As the amphiphilicity factor increases, first a disorder surface is encountered, then a Lifshitz surface, and finally a wetting transition surface. How and to what extent these surfaces move in the one-phase region toward smal1er surfactant concentrations, and intersect there with the body of heterogeneous phases, depends on a number of factors that are discussed in some detail. phase microemulsions become able to wet the water/oil interface for thermodynamic reasons. 24 Widom has suggested

The poly(ethylene oxide) (PEO)/water system is investigated using small-angle neutron scattering (SANS). This system associates to form hydrogen-bonded clusters at high enough concentrations. Two correlation lengths are observed: one long range representing cluster sizes and the other short range representing polymer chain correlations. Clusters are formed at a volume fraction of 4% hPEO in D 2O. An LCST transition is obtained between a mixed phase (through hydrogen bonding) and a demixed twophase region. Solvent deuteration is seen to enhance hydrogen bonding. Deuteration of the polymer backbone is seen to enhance hydrophobic interactions. The average polymer contrast match method fails due to the isotopic dependence of specific interactions. Pressure was seen to lower the LCST by breaking hydrogen bonds. At even higher temperature (beyond the boiling point of water) a UCST transition was observed.

Phase behavior and small angle neutron scattering (SANS) experiments were performed on mixtures of D2O/CO2/ammonium carboxylate perfluoropolyether (PFPE) surfactant as a function of pressure (192−287 bar) and D2O composition (0.8−2.0 wt %) at 35 °C. SANS measurements provided direct evidence of water-swollen inverted micelles in CO2. At a constant PFPE concentration of 2.1 wt % in CO2, the microemulsion core radius increased from 20 to 36 Å as the D2O concentration increased from 0.8 to 2.0 wt %. For a constant water concentration, parameters extracted from model fits of the SANS spectra indicated that as the phase boundary was approached on reducing pressure, micellar structure remained essentially unchanged, while critical fluctuations increased.

A new polymerizable surfactant, cetyltrimethylammonium 4-vinylbenzoate (CTVB), has been prepared and investigated. In aqueous solution, highly entangled rodlike aggregates are formed at millimolar surfactant concentrations. Free-radical polymerization of the surfactant counterions results in nearly complete conversion to a stable, nonviscous solution. Small-angle neutron scattering reveals that the micellar diameter of 40 Å is unchanged during the polymerization process and that the final polymerized micelle length (400−1200 Å) is determined by the relative initiator concentration. In addition, the parent rodlike micellar aggregates rearrange into spherical micelles at elevated temperature, whereas the polymerized structures are insensitive to temperature changes or dilution.