Search results for "angle"
showing 10 items of 1921 documents
Nanodroplets on a solid plane: wetting and spreading in a Monte Carlo simulation
2002
Abstract The wetting behavior and spreading dynamics of small polymer melt droplets in the course of transition from partial to complete wetting conditions on a flat structureless solid substrate have been studied by dynamic Monte Carlo simulation. From the density profiles of the drops we determine the contact angles at varying strength of the van der Waals surface forces in the whole interval of partial wetting. The validity of Young's equation is then tested whereby the surface tension of the melt/vapor interface is derived independently from interfacial fluctuation analysis, and the surface free energy of the melt at the substrate—from the anisotropy of the local pressure at the wall. T…
Anomalous pressure dependence of the structure factor in 1,4-polybutadiene melts: A molecular dynamics simulation study
2004
Neutron scattering has shown the first diffraction peak in the structure factor of a 1,4-polybutadiene melt under compression to move to larger q values as expected but to decrease significantly in intensity. Simulations reveal that this behavior does not result from loss of structure in the polymer melt upon compression but rather from the generic effects of differences in the pressure dependence of the intermolecular and intramolecular contributions to the melt structure factor and differences in the pressure dependence of the partial structure factors for carbon-carbon and carbon-deuterium intermolecular correlations. This anomalous pressure dependence is not seen for protonated melts.
Small-angle x-ray scattering studies of melting
1980
The course of melting of melt-crystallized polyethylene fractions and of a poly(ethylene oxide)-polystyrene-poly(ethylene oxide) triblock copolymer has been followed by small-angle x-ray scattering (SAXS). Changes in the intensity and shape of the SAXS curves indicated that both surface melting and melting over the full crystallite thickness (full-strand melting) take place. Full strand melting is the final, irreversible process. Comparison with an analytical model indicates that in the earlier stages of the irreversible, full-strand process the crystallites melt out randomly throughout the bulk. Later stages may occur by the simultaneous melting of a larger stack of crystallites.
Formation and Growth of Pd Nanoparticles Inside a Highly Cross-Linked Polystyrene Support: Role of the Reducing Agent
2014
Simultaneous time-resolved SAXS and XANES techniques were employed to follow in situ the formation of Pd nanoparticles in a porous polystyrene support, using palladium acetate as a precursor and gaseous H2 or CO as reducing agents. These results, in conjunction with data obtained by diffuse reflectance UV–vis and DRIFT spectroscopy and TEM measurements, allowed unraveling of the different roles played by gaseous H2 and CO in the formation of the Pd nanoparticles. In particular, it was found that the reducing agent affects (i) the reduction rate (which is faster in the presence of CO) and (ii) the properties of the hosted nanoparticles, in terms of size (bigger with CO), morphology (spherica…
Double implantation in silica glass for metal cluster composite formation: a study by synchrotron radiation techniques
2001
Silica glass containing metal clusters is studied for both basic and applied aspects, related to the physics of cluster formation and to the optical properties of these materials. To obtain such composite structure, Cu+ Ni, Au+ Cu, Au+ Ag, Cu+ Co, and Cu+ Ag sequential implantations in fused silica were realized. The resulting systems, after possible annealing in various atmospheres, were studied by synchrotron radiation-based techniques, namely, extended X-ray absorption fine structure (EXAFS) spectroscopy, grazing incidence X-ray diffraction (GIXRD), and grazing incidence small angle X-ray scattering (GISAXS). The unique potential of these techniques is the capability to investigate dilut…
Combined small-angle x-ray scattering/extended x-ray absorption fine structure study of coated Co nanoclusters in bis(2-ethylhexyl)sulfosuccinate
2009
Chemically stable cobalt nanostructures have been prepared with Co(II) reduction in the confined space of cobalt bis(2-ethylhexyl)sulfosuccinate, Co(AOT)2, reverse micelles dispersed in n-heptane. The reaction was carried out by adding a solution of sodium borohydride in ethanol (1% weight) to a 0.2M micellar solution of Co(AOT)2 in n-heptane at a reductant to Co(II) molar ratio of 4. This procedure involves the rapid formation of surfactant-coated Co nanoparticles followed by their slow separation as nanostructures embedded in a sodium bis(2-ethylhexyl)sulfosuccinate matrix. The resulting composites, characterized by extended x-ray absorption fine structure and small-angle x-ray scattering…
Wide Angle X-ray Scattering as a Technique of Choice to Probe Asphaltene Hierarchical Structures
2020
Bitumens are composite systems extensively used in road pavements. Due to their complex nature, a rational understanding of the relationships between composition, structure and performances of these materials is still far from being achieved, so research attempting to shed more light in this field is required. Here, we exploit Wide Angle X-ray Scattering (WAXS) as a technique of choice to shed light on the bitumen structure at different length scales. Diagnostic fingerprints, characterizing the WAXS profile, are correlated to specific Bragg distances which can be reasonably attributed to the molecular and supramolecular aggregation taking place at various levels of complexity leading to the…
Fractal approach in petrology: Combining ultra small angle (USANS), and small angle neutron scattering (SANS)
2000
Ultra small angle neutron scattering instruments have recently covered the gap between the size resolution available with conventional intermediate angle neutron scattering and small angle neutron scattering instruments on one side and optical microscopy on the other side. Rocks showing fractal behavior in over two decades of momentum transfer and seven orders of magnitude of intensity are examined and fractal parameters are extracted from the combined USANS and SANS curves.
Effect of hydraulic coefficient on membrane performance for rejection of emerging contaminants
2018
International audience; The efficient removal of Endocrine Disruptive Chemicals (EDCs) namely oxybenzone and atrazine using polysulfone (PSf) composite membranes is reported in this article. A negatively charged hydrophilic mixed matrix membrane was prepared by using Polyaniline modified halloysite nanotubes (PANi-HNT) and polysulfone. The X-ray diffraction (XRD) and attenuated total reflectance infrared (ATR-IR) technique confirm the conversion of Halloysite nanotubes to Polyaniline modified halloysite nanotubes and their presence in membrane matrix. The microvoids observable in the SEM images depict the internal structure of the membrane. Further, increasing in the water uptake and decrea…
Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders
2016
Bitumen is a viscoelastic material that exhibits both elastic and viscous components of response and displays both a temperature and time dependent relationship between applied stresses and resultant strains. In addition, as bitumen is responsible for the viscoelastic behaviour of all bituminous materials, it plays a dominant role in defining many of the aspects of asphalt road performance, such as strength and stiffness, permanent deformation and cracking. Although conventional bituminous materials perform satisfactorily in most highway pavement applications, there are situations that require the modification of the binder to enhance the properties of existing asphalt material. The best kn…