Neutron solution scattering

The experimental techniques for the study of conformational branched properties in solution are the same as used for linear chains. These are, in particular, static and dynamic light scattering, small angle X-ray (SAXS) and small angle neutron (SANS) scattering methods, and common capillary viscometry. These methods are supported by osmotic pressure measurements and, nowadays extensively applied, size exclusion chromatography (SEC) in on-line combination with several detectors. These measurements result in a list of molecular parameters which are given in Table 1. 

The surfactant AOT forms reverse micelles in non-polar fluids without addition of a cosurfactant, and thus it is possible to study simple, water/AOT/oil, three component systems. To determine micelle structure and behavior in water/AOT/oil systems, investigators have studied a wide range of properties including conductivity (15), light (JL ), and neutron (12) scattering, as well as solution phase behavior (1 ). From information of this type one can begin to build both microscopic models and thermodynamic... 

The narrow band-width obtained with crystal monochromators allows the resolution of bands in the solution scattering patterns which would not be possible with neutrons, where high fluxes can only be achieved by using a large bandpass (AX/X 0.08). 

Fig. 2. Schematic variation of neutron scattering density for an object composed of a central sphere of RNA and a concentric outer shell of protein, i.e. a simple virus. The contrast difference dp is the difference between the scattering density of the solvent pg and the solute py. High positive and negative dp are seen in 0 and 100% H20. The protein shell is matched-out in 43% H20 and the RNA core is matched-out in 72% H20. Note that for reason of solvent H- H exchange, the average protein and RNA densities increase slightly on going from 0 to 100% H20. Solution scattering is observed where the solute and solvent densities are different. Note that the fluctuations in scattering densities pp(r) within each of the protein and RNA components do not disappear at their respective matchpoints. See Section 2.3 for a further explanation of the terms in dp, ps, Py and Pp(r).

Diffraction methods. Bombardment of aqueous solutions of electrolytes by neutrons or X-rays causes scattering which is characteristic of the microscopic structure of the system. X-rays are preferentially scattered by heavy atoms whereas neutrons are scattered best by the lightest atoms. Direct determination of the number and geometry of the water molecules in the primary hydration sphere of the lanthanides have been attempted by both techniques. 

At the intermediate wavelengths no useful analytic forms of solution are known. On the other hand, (138) yields readily to numerical solutions. Such results show a smooth interpolation between characteristic hydrodynamic and free-particle behavior. Notice, however, that in this region it is essential to treat the collisions and molecular flow on equal footing for this reason it would be inappropriate to apply either (154) or (155). Since the intermediate k range is particularly relevant to neutron inelastic scattering studies of liquids and related computer molecular dynamics simulations, the validity of our kinetic model solutions is of interest. 

Figure 28a displays a typical three-dimensional plot of the neutron intensity scattered by a nematic lyotropic solution in the (qv,qvv)-plane. The data were obtained on the SDS/Dec calamitic phase at 50 s (concentration c = 29.5 wt. % and R = [Dec]/[SDS] = 0.33). As shown in the iso-intensity contour plot (Fig. 28b), the patterns are characterized by two crescent-like peaks aside from the velocity axis. The maximum scattering corresponds to the first order of the structure factor, from which the distance between the center-of-mass of the micelles can be estimated (here 6 nm for a radius of nm). The modulation of the azimuthal intensity is also of interest since it reflects the distribution of micellar orientations. The spectra were analyzed in terms of angular distribution of the scattered intensity. The scattering was integrated over an elementary surface dgvdgvv = where corresponds typically to the half width at half... 

Lattice vibrations can be measured experimentally by means of classical vibration spectroscopic techniques (infrared and Raman) or neutron inelastic scattering. However, only the latter technique allows one to measure the full spectrum in a range of k vectors, whereas with infrared and Raman spectroscopy, only lattice vibrations at r k = 0) are usually detected (the second-order spectra, corresponding to nonzero wavevector k 0 are demanding). The calculations of the vibrational frequencies only at F point require the solution of only one equation... 

A review is presented of some recent applications of neutron vibrational spectroscopy to the study of disordered metal-hydrogen systems. The examples discussed cover a range of systems from simple dilute solutions in bcc or fee metals to amorphous alloy hydrides. It is shown that neutron inelastic scattering studies of the vibrational density of states provide a powerful and sensitive probe of the local potentials and bonding sites of hydrogen in metals and often reveal critical information on the novel microscopic physical properties and behavior of disordered metals-hydrogen systems, including those influenced by interstitial or substitutional defects. 

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