Neutron-scattering-density profiles

FIGURE 9.2 Neutron-scattering-density profiles p(z) for a lithium-substituted vermiculite. Oxygen plus clay layer is the solid line, hydrogen is the dashed line, and lithium is the stars. The molecular model above shows two sections of clay surface and an undistorted octahedral Li+(H20)6 complex. In this model all six water molecules are hydrogen bonded directly to the clay plate in practice we find that, on average, two of the six water molecules are less strongly oriented toward the plate. 

Fig. 12. a Neutron reflectivity data for a 860 A-thick PMDA-3F/PPO triblock film which has been foamed for 4 h. The line through the data is the fit using the scattering density profile shown in b. b Scattering length density profiles for a unfoamed and foamed PMDA-3F/PPO triblock. The foaming results in a decrease in the overall film thickness and an increase in the density of the skin layer, particularly at the air interface. The density in the center of the film corresponds to about 15% voids, density skin at the top and bottom surfaces of the film... 

Several experimental parameters have been used to describe the conformation of a polymer adsorbed at the solid-solution interface these include the thickness of the adsorbed layer (photon correlation spectroscopy(J ) (p.c.s.), small angle neutron scattering (2) (s.a.n.s.), ellipsometry (3) and force-distance measurements between adsorbed layers (A), and the surface bound fraction (e.s.r. (5), n.m.r. ( 6), calorimetry (7) and i.r. (8)). However, it is very difficult to describe the adsorbed layer with a single parameter and ideally the segment density profile of the adsorbed chain is required. Recently s.a.n.s. (9) has been used to obtain segment density profiles for polyethylene oxide (PEO) and partially hydrolysed polyvinyl alcohol adsorbed on polystyrene latex. For PEO, two types of system were examined one where the chains were terminally-anchored and the other where the polymer was physically adsorbed from solution. The profiles for these two... 

Fig. 2.54 Neutron reflectivity profile for a symmetric PS-dPMMA diblock (Mw 30 kg moP1) as a function of incident wavevector (Russell 1990). The inset shows the scattering length density (b/V, the neutron scattering length per unit volume) profile normal to the film surface that was used to calculate the reflectivity profile shown as the solid line, This is typical of a block copolymer film containing a multilayer stack, with lamellae parallel to the surface.

Fig. 2.59 Neutron reflectivity profiles for a PS-riPMMA symmetric diblock copolymer (Mw = 29.7kgmor ) film of total thickness 5232 A (Menelle et al. 1992). Experiments were performed on samples annealed at the temperatures shown. The solid lines were computed using the scattering length density profiles shown in the insets, which show that the surface induces lamellar order even above the bulk ODT 157 8°C (the air-polymer interface is located at z - 0). 

Fig. 9 Density profiles of PEE-PSSH micelles for varying salt concentrations. The profiles were obtained by a combination of static and dynamic light scattering, small-angle neutron scattering and cryo-TEM [49]...

The measured reflectivity, R(Q), depends upon the neutron refractive index profile perpendicular to the interface, defined as the z-direction. The neutron refractive index is a function of the scattering length density, Nb, which is the product of the number density N, in units of nuclei per cm3, and the neutron scattering lengths, b, of the nuclei present. Since the neutron scattering length varies from nucleus to nucleus, chances in the nature and composition of the surface result in changes in reflectivity. 

Figure 4.29 Scattering length density profiles for an [Os(bpy)2(PVP)ioCl]Cl film in (a) perchloric acid, and (b) p-toluene sulfonic acid at different pff levels. From R.W. Wilson, R. Cubitt, A. Glidle, A.R. ffillman, P.M. Saville and J.G. Vos, A neutron reflectivity study of [Os(bpy)2(PVP)ioCl]+ polymer film modified electrodes effect of pff and counterion, /. Electrochem. Soc., 145,1454-1461 (1998). Reproduced by permission of The Electrochemical Society, Inc...

The normalized neutron scattering intensities, 1(Q), are related to the neutronscattering density profiles normal to the clay sheets, p(z), via the crystallographic structure factor, S(Q), as... 

X-ray and neutron specular reflection Molecular structure across the interface, laterally averaged over the beam area X-rays electron density profiles neutrons scattering length density profiles of the nuclei of atoms). With neutrons different parts of the monolayer can be studied independently by selective H/D substitution. See ellipsometry. 

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