SAXS measurement

Section 2 of this chapter describes the characterization of carbonaceous materials by powder X-ray diffraction, small-angle-X-ray scattering (SAXS), measurements of surface area, and by the carbon-hydrogen-nitrogen (CHN) test, a chemical analysis of composition. In this section, we also describe the electrochemical methods used to study carbonaceous materials. 

Fig. 4. Schematic showing the SAXS measurement on the Siemens D5000 diffractometer. The wave-vector, k, is determined as (2-kIX) ss, where s and s are the umt veetors defining the directions of the seattered and incident radiation respectively.

A Siemens Kratky camera system was utilized for small angle x-ray scattering (SAXS) measurements in conjunction with an M. Braun position sensitive detector from Innovative Technology Inc.. Wide angle x-ray diffraction was obtained utilizing a Philips table-top x-ray generator. 

It has been shown above that during the induction period no change occurs in DSC, macroscopic density, and WAXD. Does nothing change in this period In order to answer this question, we made real-time SAXS measurements. 

This problem is very important, but it is extremely difficult to make SAXS measurements at higher temperatures because the induction period becomes too short to observe the time evolution of SAXS intensities. For example, as was seen in Sect. 2.2, the induction period was only 100 s when the PET glass was crystallized even at 115 °C, 40 K higher than Tg, where a detailed analysis of the SAXS data was impossible. Of course, as the crystallization temperature approaches the melting temperature, the induction period is expected to become longer. However, as will be shown below, no characteristic peaks of SD could be detected in SAXS curves either. This is probably because the crystallization temperature was not in the unstable state, or the characteristic wavelength was much larger compared with the lower resolution limit of... 

SAXS measurements on solid films of the block copolymers underscore the high degree of order inside these films. Figure 10.7 shows some SAXS difiacto-grams and the corresponding microstructures that we found in our block copolymers. Here, we are only able to present some preliminary data. A detailed discussion of all the investigated block copolymers will follow in a later publication.16... 

SAXS is sensitive to variations in the electronic density in a material, and so provides information about the shape and size of clusters in micro PS. In contrast to the quantum wire structure proposed in early publications [Cal, Lei], the crystallites in micro PS are found to be almost spherical. There has been some evidence that the dimensions in the growth direction are somewhat smaller than those parallel to the surface [Fr2], The latter result, however, is still controversial because investigations by spectroscopic techniques indicate an opposite elongation [Mi4], A combination of grazing incidence diffraction (GID) and SAXS measurements on various freestanding micro PS films showed crystallite diameters from about 1.5 to 4 nm, depending on formation conditions. A good correlation between size reduction and blue shift of the PL peak position has been observed [Bi3],... 

Figure 1. Model of CBH I deduced from SAXS measurements proposed 1986 (from ref. 24 with permission of the authors).

Figure 2. Model of CBH I deduced from a second series of SAXS measurements (redrawn from ref. 25 with permission).

At present we do not yet have sufficient information to determine whether the annealing process exerts an effect primarily through changes in chain conformation or the distribution of ionic aggregates, or both. Measurements of Tg showed no change for annealed vs. unannealed samples, while SAXS measurements were inconclusive and require repetition. Further Mossbauer measurements would also be required before definitive conclusions of this nature could be drawn. 

A more quantitative measure of the microfibrillar morphology can be obtained by SAXS measurements. A detailed analysis of the small-angle scattering from PBT films and derivation of the relevant equations will be given elsewhere. The main features of the analysis are given below. 

Using Equations 3-5, with the densities of the impregnated film and the epoxy matrix measured independently, the following characteristics of the microfibrillar network can be calculated from the SAXS measurements (Y. Cohen and E. L. Thomas to be published) ... 

In an attempt to separate the domains from the cores, we used limited degradation with several proteases. CBH I (65 kda) and CBH II (58 kda) under native conditions could only be cleaved successfully with papain (15). The cores (56 and 45 kda) and terminal peptides (11 and 13 kda) were isolated by affinity chromatography (15,16) and the scission points were determined unequivocally. The effect on the activity of these enzymes was quite remarkable (Fig. 7). The cores remained perfectly active towards soluble substrates such as those described above. They exhibited, however, a considerably decreased activity towards native (microcrystalline) cellulose. These effects could be attributed to the loss of the terminal peptides, which were recognized as binding domains, whose role is to raise the relative concentration of the intact enzymes on the cellulose surface. This aspect is discussed further below. The tertiary structures of the intact CBH I and its core in solution were examined by small angle X-ray scattering (SAXS) analysis (17,18). The molecular parameters derived for the core (Rj = 2.09 mm, Dmax = 6.5 nm) and for the intact CBH I (R = 4.27 nm, Dmax = 18 nm) indicated very different shapes for both enzymes. Models constructed on the basis of these SAXS measurements showed a tadpole structure for the intact enzyme and an isotropic ellipsoid for the core (Fig. 8). The extended, flexible tail part of the tadpole should thus be identified with the C-terminal peptide of CBH I. 

SAXS measurements with CBH II indicated a very similar tertiary structure for both CBH I and CBH II, in spite of a different domain arrangement (to be published). Discrete differences in the tail parts could, however, be noticed. The maximum diameter of CBH II (21.5 nm) was higher than in CBH I this might be due to duplication of the glycosylated part in the former case. Thus, the functional differentiation of these cellulases can be reflected by structural differences. 

Figures 6.2 and 6.3 compare the SANS scattering responses, for RH=0.11 and RH=0.87, of the dry carbon, the carbon+TD, carbon+0 0, and carbon + D O+TD. The loss of intensity due to the reduced contrast factor is evident in the region 0.2A

Other modifications to the reaction conditions of the Brust-Schiffrin method, such as a reduction temperature of — 78 °C and the use of a hyperexcess of hexanethiol, results in an Au38(thiolate)24, based on observations, LDI-TOF mass spectrometry, TGA analysis and elemental analysis [69]. The influence of preparation temperature on the size and monodispersity of dodecylthiol monolayer protected gold clusters has also been reported. Both and SAXS measurements show that higher temperatures increase polydispersity. This modification of poly-dispersity may be related to the existence of a dynamic exchange of thiols at the particle surface with thiols in the solvent [70]. 

The effect of temperature on g is difficult to predict because effects such as solvatation, entropic thermodynamic have to be taken into account. Thus the phase transition of MCM-41 to MCM-48 can not be explained by using the packing parameter g when crystallization temperature increases. Some complementary studies (synthesis at lower and higher temperatures, XRD or SAXS measurements...) should be made to understand and explain the mechanism of phase transition. 

Figure 4. Microfocus synchrotron SAXS measurements Thickness T (nm) and Shape (rj) parameters ofcalcium-iron-phosphate features from the midden profile at Vollen, Langenesvceret, Norway. (Reproducedfrom Reference 32. Copyright 2004 Elsevier)...

Complexation of 100 with carbonyl complexes of chromium, molybdenum, and tungsten yielded liquid crystalline complexes lOla-c [114] (Scheme 50). All derivatives 101 melted at similar temperatures into the columnar rectangular mesophase (deduced from WAXS and SAXS measurements). However, the clearing points were strongly dependent on the metal center and increased with increasing atom number. Upon complexation, the aza crown macrocycle loses its flexibility, with the metal carbonyl fragment located above the crown leading to a cone-shaped... 

Fig. 35 Crystallization of non-spherical particles homogeneously coated with DNA. (a, b) Schematic of a hexagonal close-packed 2D layer in assemblies of gold nanorods and corresponding structure factor S(q) obtained from SAXS measurements (blue line) and simulations (red line), (c, d) Schematic of ID columnar assembly of gold triangular nanoprisms and corresponding SAXS patterns, (e, f) Schematic of the 3D fee assembly of gold rhombic dodecahedra (the lines indicate the fee unit cell) and corresponding SAXS patterns. Adapted with permission from [152]...

Reaction-induced phase separation is certainly also the reason for which an inhomogeneous structure is observed for photocured polyurethane acrylate networks based on polypropylene oxide (Barbeau et al., 1999). TEM analysis demonstrates the presence of inhomogeneities on the length scale of 10-200 nm, mostly constituted by clusters of small hard units (the diacrylated diisocyanate) connected by polyacrylate chains. In addition, a suborganization of the reacted diisocyanate hard segments inside the polyurethane acrylate matrix is revealed by SAXS measurements. Post-reaction increases the crosslink density inside the hard domains. The bimodal shape of the dynamic mechanical relaxation spectra corroborates the presence of a two-phase structure. 

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