Crystalline reflection

Figure C2.17.8. Powder x-ray diffraction (PXRD) from amoriDhous and nanocry stalline Ti02 nanocrystals. Powder x-ray diffraction is an important test for nanocrystal quality. In the top panel, nanoparticles of titania provide no crystalline reflections. These samples, while showing some evidence of crystallinity in TEM, have a major amoriDhous component. A similar reaction, perfonned with a crystallizing agent at high temperature, provides well defined reflections which allow the anatase phase to be clearly identified.

Figure 3 Non-linear least-squares curve fitting of the orthorhombic WAXS profile of an ethylene 1-decene random copolymer with 2.7 mol% branches. The two crystalline reflections and the amorphous halo are shown. 

How much of a crystallizable material X can I blend uniformly into a polymer until it starts to form crystals A series of blends with increasing amount of X is prepared. The samples are studied by WAXS (cf. Sect. 8.2) using laboratory equipment. Crystalline reflections of X are observed, as X starts to crystallize. Peak areas can be plotted vs. the known concentration in order to determine the saturation limit. Think of X being Ibuprofen and Y a polystyrene-(7 )-polyisoprene copolymer, and you have an anti-rheumatism plaster. 

A simple phenomenological method can be used to describe changing crystallinity from WAXS data of isotropic materials. It is based on the computation of areas in Fig. 8.2. First we search the border between first-order and second-order amorphous halo. For PET this is at 29 37° (vertical line in the plot). Then we integrate the area between the amorphous halo and the machine background. Let us call the area Iam. Finally we integrate the area between the crystalline reflections and the amorphous halo, call it Icr, and compute a crystallinity index... 

The electron dose needed for complete disappearance of all crystalline reflections in the SAED pattern is termed the total end-point dose (TEPD),... 

Fig. 14 Wide-angle X-ray diagrams of crystalline all-trans retinoic acid (curve a) and its complexes with polyamino acids. In the curve of poly(L-arginine) retinoate and poly(L-lysine) retinoate (curves b and d, respectively) no crystalline reflections were found. However, three weak crystalline reflections are present in the curve of poly(L-histidine) retinoate at s=1.69, 2.48 and 2.73 nm-1 (curve c). This is indicative of a partially crystalline complex structure. Reprinted with permission from [142]. Copyright 2000 American Chemical Society...

The Ru02 particles can not be reduced at room temperature, but reduce readily at 773 K. The ruthenium particles produced after this reduction procedure are estimated to be 16 nm in diameter from x-ray diffraction line width analysis. The reduction results in further loss of crystallinity, reflected by a drop in surface area and microporosity (Table 2). In addition, the position of the asymmetric T-O stretching vibration is at 1071 cm" 1, indicating a very silicon-rich material. 

Figure 3. WAXS patterns of the as-reacted PCP/MDI/BDO polymers (upper left) 1/2/1, (upper right) 1/3/2, (lower left) 1/4/3, and (lower right) 1/6/5. All samples except upper left exhibit hard-segment crystalline reflections.

Experiments were performed using a Phillips PW-3010 automated powder diffractometer with CuKa radiation (40mA, 40kV). Measurements of the crystal unit cell size (u.s.c.) [19] and hence the framework Si/Al ratio ((Si/Al)jy) [20] as well as the crystallinity of the zeolites were obtained, and are given in Table 1, for the parent and hydrothermally treated zeolites, and in Table 3 for the AHFS treated zeolites. As expected, both the u.c.s (framework Si/Al ratio) and crystallinity reflect the degree of steam treatment in the hydrothermally treated... 

Thus the structural and mechanical data are mutually compatible and point to an Increase In the order of the hard domains as a result of use of the PEDA additive, comparable to that which Is achieved by annealing without use of the additive. At present we can only speculate on the mechanism whereby the PEDA leads to the higher order. The crystalline reflections are those of homopoly (MDI/EG) and hence the PEDA chains must be outside the crystalline regions, but the flexural modulus does Increase Indicating some hard domain association. Nevertheless, the PEDA could be Intimately Involved with the hard domains. The amine groups are much more reatlve than the hydroxyls of the chain extender and polyol, and hence the first chemical reaction will Involve PEDA and MDI. The MDI-PEDA-MDI units may serve as nucleatlon agents for the formation of the hard domains, perhaps because of their low solubility In the reaction mixture. 

Film stretching is used as a very efficient way to identify the crystalline reflections, as already described in Section 4. Stretching certainly orients the crystalline parts with the polymer chains preferentially along the stretch direction. Stretching is observed to enhance the crystallinity of some polymers, like polyanilines [108], but such an effect has not been reported for poly(alk-ylthiophene)s. There is evidence that stretching also imposes anisotropy on the amorphous part [69,73]. 

It is well known that chitin is a semicrystalline polymer. Consequently, it is necessary to verify whether chitin s crystalline volume fraction changes with heat treatment and its influence on relaxation behaviors. The diffraction pattern of purified a-chitin powder is shown in Figure 2.8. The five characteristic crystalline reflections for a-chitin are present [51]. They are indexed as (020), (110), (120),... 

The X-ray diffraction studies have been interesting in supporting the observations on the crystallinity of membranes determined by DSC. The crystalline reflections in graft copolymer membranes with different degrees of grafting fall on identical angles. However, their intensity decreases, suggest-... 

Most of the polyimides were amorphous in nature. This was because of the various structural modifications onto the polymer backbone. In general, polyimides derived from dianhydrides such as PMDA, BPDA and BTDA exhibited higher crystallinity than the other dianhydrides such as OPDA, DSDA and 6FDA. The higher crystallinity reflected on their poor solubility. 

CRYSTALLINE REFLECTANCE SPECTRA OF ION-RADICAL SALTS AT ROOM TEMPERATURE, AT 77 AND AT 4.2 K. I. 

Further studies have indicated considerable differenees in the x-ray scattering characteristics of coal components and that certain high-rank coals gave rise to the three-dimensional crystalline reflections of graphite. After a further systematic study of several high-rank coals,... 

Asano and Seto [259] interpreted the equatorial broad halo as due to overlap of four crystalline reflections of a paracrystalline monoclinic structure. The presence of the meridional reflections at d = 10.3 A was explained by a tilt of 10° of c axis of the monoclinic unit cell with respect to the drawing direction this is analogous to the triclinic structure of PET studied by Bunn [258], for which X-ray diffraction patterns of well-oriented fibers... 

Figure 6a gives a typical SAXS picture of the shear-induced smectic peak at 200 °C an accompanying smectic WAXS peak may be hidden in the amorphous halo of the corresponding pattern in Fig. 6b [152]. At this temperature no crystallization is expected at all, as confirmed by the absence of any crystalline reflections in both SAXS and WAXS. The smectic SAXS intensity is...

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