Search results for "scattering"

Neutron Scattering of Poly(ethylene terephthalate)

1986

Through the use of deuterium labeling, small angle neutron scattering (SANS) has been found to be an extremely effective tool for elucidating the structure of polymer molecules in the condensed matter state. In this study, the molecular morphology of poly(ethylene terephthalate) (PET) has been determined under four different conditions: (1) in the glassy state, (2) in the semicrystalline state, (3) after cold-drawing, and (4) after undergoing partial transesterification.

1985

Etude des phases isotrope, nematique et smectique de melanges de polymeres protones et en partie deuteries

Modelling small angle neutron scattering data from polymers in supercritical fluids

2000

In this paper we report a SANS investigation of micelle formation by fluorocarbon-hydrocarbon block copolymers in supercritical CO2(scCO2) at 313K. A sharp unimer-micelle transition is obtained due to the tuning of the solvating ability of scCO2 by profiling pressure. At high pressure the copolymer is in a monomeric state with a random coil structure. By lowering the pressure aggregates are formed with the hydrocarbon segments forming the core and the fluorocarbon segments forming the corona of spherical aggregates. This aggregate-unimer transition is driven by the gradual penetration of CO2 molecules toward the core of the aggregate and is critically related to the density of the solvent, …

Small-Angle Scattering Techniques for Analyzing Conformational Transitions in Hemocyanins

2004

Publisher Summary The precise delivery of oxygen from respiratory surfaces to the tissues is mediated by cooperative and allosterically regulated carrier proteins, such as hemoglobin or hemocyanin. To establish cooperativity, these proteins must be able to adopt different conformations. These conformations are characterized by different ligand affinities, which have their basis in different structures as is the case for the deoxy and oxy states of human hemoglobin. To understand the cooperative interaction of these molecules at the molecular level, the structures of these conformations must be resolved and the transitions between them must be monitored. Because of the nature of sample prepa…

Neutron-scattering studies on CeM2Ge2(M=Ag, Au, and Ru)

1992

The results of elastic, quasielastic, and inelastic neutron-scattering studies on polycrystalline CeM 2 Ge 2 (M=Ag, Au, and Ru) are presented. All compounds reveal long-range magnetic order at low temperatures. Ferromagnetic (M=Ru), antiferromagnetic (M=Au), and incommensurate (M=Ag) structures were detected. Using time-of-flight (TOF) techniques, the crystalline electric-field splittings were determined. With high-resolution TOF experiments the temperature and wave-vector dependence of the magnetic relaxation rate was studied

1984

Provided a polymer is soluble, i. e., molecularly dispersed in another polymer irrespective of the molecular weight of the components, the solution is exothermic. By increasing the temperature two effects, both unfavourable to mixing become larger: (i) the excess entropy of mixing caused by contact interaction and (ii) the total effect from the difference of the free volumes of the pure components. So, an upper miscibility gap occurs. The thermodynamic properties of the mixture cannot be derived from the properties of the pure components. They can be described by the corresponding states theory of Prigogine, Flory, and Patterson with suitable values for the contact energy and contact entrop…

Beiträge zur polymerisation von 2-isopropenylnaphthalin, 3. Anionische homopolymerisation von 2-isopropenylnaphthalin

1981

The anionic homopolymerization of 2-isoprenylnaphthalene with butyllithium in tetrahydrofuran at –78°C is described. The refractive index increment amounts to dn/dc = 0,2084 ml/g for these polymers in toluene at 25°C and wavelength λ = 436 nm. Determination of the molecular weights by light scattering yielded values between 13 000 and 270 000. The second virial coefficients also determined by light scattering measurements are comparable with the corresponding data of poly(α-methylstyrene). A calibration curve is given for gel permeation chromatography of the poly(2-isoprenylnaphthalene)s, whose polymolecularity indexes Mw/Mn lie between 1,06 and 1,2. Their intrinsic viscosity/molecular weig…

Behaviour of modified and unmodified polybutadienes in the semidilute regime

1997

Abstract The association behaviour of polybutadiene modified with 4-phenyl-l,2,4-triazoline-3,5-dione was studied in semidilute solution through static (SLS) and dynamic light scattering (DLS). The results were compared with the unmodified polybutadiene, whose behavior in semidilute solution was also studied as function of the molecular weight. At higher concentrations a small-angle excess scattering in SLS and a slow mode motion in DLS were observed both for modified and unmodified polybutadienes suggesting the presence of large clusters. Increasing the polymer concentration, the mass fraction of the slow motion increases up to values near 1, indicating a proximity to the gel point. For po…

Structural characterization of frozen n-heptane solutions of metal-containing reverse micelles

2007

The microstructure of temperature-quenched solutions of reverse micelles formed by sodium, cobalt, ytterbium, and cobalt/ytterbium bis(2-ethylhexyl)sulfosuccinate in n-heptane has been investigated by SAXS and EXAFS. Some changes in the X-ray absorption spectra with respect to the same systems at room temperature have been observed. The analysis of the SAXS spectra leads to the hypothesis that at 77 K the closed spherical structure of reverse micelles is retained and that during the temperature quench they undergo a clustering process involving the transition from a quite random dispersion to the formation of more or less large clusters of strongly packed reverse micelles. This behavior is …

Effects of isotopic substitution on the conformational properties of polymeric aqueous solutions

2000

Abstract This work deals with a side-by-side comparison between the PEO conformational properties in H 2 O and D 2 O. The gyration radius, evaluated by SANS, the hydrodynamic radius, evaluated by PCS, and the Raman D-LAM band analysis furnish valuable information on the structural arrangement of the molecules. The findings clearly show different behavioural properties of the polymer in H 2 O and D 2 O.