Search results for " Small"

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.

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…

Polyaspartamide-based nanoparticles loaded with fluticasone propionate and the in vitro evaluation towards cigarette smoke effects

2017

This paper describes the evaluation of polymeric nanoparticles (NPs) as a potential carrier for lung administration of fluticasone propionate (FP). The chosen polymeric material to produce NPs was a copolymer based on α,β-poly(N-2-hydroxyethyl)-d,l-aspartamide (PHEA) whose backbone was derivatised with different molecules, such as poly(lactic acid) (PLA) and polyethylenglycol (PEG). The chosen method to produce NPs from PHEA-PLA-PEG2000 was the method based on high-pressure homogenization and subsequent solvent evaporation by adding Pluronic F68 during the process and trehalose before lyophilisation. Obtained colloidal FP-loaded NPs showed a slightly negative surface charge and nanometric d…

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.

Determination of the Composition of Mixed Hydrogenated and Fluorinated Micelles by Small Angle Neutron Scattering

1997

Microwave characterization and modeling of packaged HEMTs by a direct extraction procedure at cryogenic temperatures

2004

In the present work we employ a direct extraction procedure to determine small signal equivalent circuit of microwave GaAs FETs by means of scattering (S-) parameter measurements down to cryogenic temperatures. The direct extraction procedure was tested on packaged AlGaAs/InGaAs HEMTs and good agreement between the simulated and measured S-parameters was obtained at different bias and temperature conditions. We employed a properly designed cryogenic set-up operating in our laboratory that allows to perform DC and RF characterization down to 30 K.

Scattering perspectives on nanostructural inhomogeneity in polymer network gels

2017

Abstract Scattering methods based on spatial and temporal contrast fluctuations in polymer-network gels, which originate from polymer-segmental density fluctuations, reveal rich insight into different types and levels of nanostructural inhomogeneity in these soft materials. Complementary contrasting as provided by light, neutron, and X-ray scattering allows such information to be obtained on nano- to micrometer length scales. On top of that, complementary use of static and dynamic scattering methods allows the interplay and effect of these inhomogeneities to be unraveled. This article interrelates a multitude of studies on the application of scattering techniques for analytical assessment o…

Neutron Scattering Studies on the Crystallization of Polymers

1985

Abstract Neutron scattering on mixtures of deuterated and undeuterated molecules offer a new approach for solving long standing problems of the structure of semicrystalline polymers. The various ranges of the amount of the scattering vector q yield different informations. From small angle studies the radius of gyration Rg can be obtained, which does not change markedly by crystallization. The scattering intensity in “the intermediate angle range yields mainly the average distance of the crystalline stems. Experimental results show that not only Rg remains almost constant, but that also the pair distribution function g(r) of the monomer units for r«Rg does not change appreciably during cryst…

Chain conformation and structure in amorphous polymers as revealed by X-ray, neutron, light and electron diffraction

1976

Abstract The physical structure of the melt, the supercooled melt, and the glassy state of amorphous polymers can be characterized by the chain conformation, the local order, and the morphology. The conformation was studied by small-angle neutron scattering. The local order was characterized by pair distribution functions which were derived from electron scattering curves. In addition, model calculations were used to gain information about short-range order. The morphology was studied by means of light scattering (density and anisotropy fluctuations), small-angle X-ray scattering (density fluctuations), and magnetic birefringence measurements (orientational order). Experiments were performe…