Spacing Bragg

The wide-angle (201) reflection is strong, whereas the (200) reflection at 4.7 A Bragg spacing is much weaker or nonexistent for A8A and lyophilized HI, or is nearly as strong as the (201) reflection for SHal06-122 and solubilized/dried HI. Because the intersheet distance of polyalanine is —5 A, the unit cell should contain two //sheets. 

A variation of the lamellar model was recently proposed by Haubold et al., in which synchrotron SAXS studies were performed on acid form Nafion 117 samples. The molecular weight of these samples was reported to be 250 000 g mol and the experiments were conducted on dry samples in air and samples equilibrated with water, methanol, and a range of water/methanol mixtures using an in situ flow cell. The most fundamental result of this study is that the data show the usual ionomer peak at = 1.4 nm which gives a Bragg spacing of d= Zjtlq ... 

On a finer level, spherical grains that have an average diameter of 11 A are seen. A section analysis, which consisted of a plot of image contrast intensity versus distance, indicated that there is a mean periodicity of around 49 A, which is close to the values of the SAXS Bragg spacing usually associated with intercluster distances. This, as well as other microscopic studies, favors the model of phase separation as opposed to the core—shell model as applied to the interpretation of scattering data. The hydrated... 

A) A clear scattering maximum In 24% PBLG/DMF/H2O (trace). The Bragg spacing Is 6ym. B). Photomicrograph of same sample as A between crossed polars. The correlation distance appears to be about 9vtm. 

Figure 5 A schematic model of the formation of lipid gel phase by hydration of the polar groups in crystalline regions of emulsifiers, d = interplanar Bragg spacing d, = thickness of lipid bilayer dw = thickness of water iayer. Redrawn from reference 15, courtesy of Marcel Dekker Inc.

In Ni(pc)I and Ni(tbp)I, the iodine superlattice spacing, c, is a multiple of the Bragg spacing, c (c = 3/2 c), so the superlattice is commensurate with the Bragg lattice and the repeat unit contains three Bragg sites. The disorder in these two systems is not severe, and could be modeled satisfactorily2,132,116 No special treatment of the iodine atoms was necessary to solve the Bragg structures, and the only structural manifestation of the... 

The lamellar structure is characterized by low-angle X-ray patterns exhibiting a set of sharp lines with Bragg spacings in the ratios 1,2, 3, 4, 5. ... and by micro-... 

The total thickness d = dA + dB of a sheet is directly given by the Bragg spacing of the X-ray patterns, or directly measured on the electron micrographs (to obtain an accurate value of d by electron microscopy one must use electron micrographs provided by sections perpendicular to the planes of the sheets, this is easy with an electron microscope equipped with a goniometer head). 

D is directly measured on electron micrographs or directly obtained from the Bragg spacings of X-ray patterns, 2 R is directly measured on electron micrographs or calculated from the value of D given by X-rays using the following formulae ... 

Figure 10. X-ray powder scattering patterns for the trans and cis model compounds of the BBB repeat unit and for BBB. The scale indicates Bragg spacings in Angstroms...

Table II shows the Bragg spacing and the sum of the unperturbed block dimensions for PPO 3000/50 and 3000/25, < r0 > was estimated from the values for PPO, and poly (oxyethylene oxyterephthaloyl) given in the literature (26). As the average block molecular weight increased, the Bragg spacing also increased and is the same order of magnitude as the unperturbed block dimensions. This can be taken as a clear indication that phase separation of the blocks has occurred in PPO 3000/50 and 3000/25.

Figure 8 Scattering curve from human SC after heating to various temperatures followed by cooling to room temperature. The temperatures to which the SC was heated are indicated, n = 1, 2, etc. refer to the orders of diffraction peaks from a lamellar structure with a Bragg spacing of 134 A. n = I, II refer to peaks corresponding to a lamellar structure with Bragg spacing of 64 A. (Data from Bouwstra et al., 1991.)...

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