Amorphous samples

Q are the absorbance and wavenumber, respectively, at the peak (center) of the band, p is the wavenumber, and y is the half width of the band at half height. Liquid band positions ate usually shifted slightly downward from vapor positions. Both band positions and widths of solute spectra are affected by solute—solvent interactions. Spectra of soHd-phase samples are similar to those of Hquids, but intermolecular interactions in soHds can be nonisotropic. In spectra of crystalline samples, vibrational bands tend to be sharper and may spHt in two, and new bands may also appear. If polarized infrared radiation is used, both crystalline samples and stressed amorphous samples (such as a stretched polymer film) show directional effects (28,29). 

Clathrate structures have been recently obtained also for s-PS [8] and s-PPMS [10]. In particular for s-PS, the treatment of amorphous samples, as well as of crystalline samples in the a or in the y form, produces clathrate structures including helices having s (2/1)2 symmetries, which present similar diffraction patterns, independently of the considered solvent. The treatment of samples of s-PPMS with suitable solvents also produces clathrate structures including s(2/l)2 helices however, the large differences in the X-ray diffraction patterns suggest different modes of packing, depending on the included solvent. 

Figure 3 The Cns ESCA spectrum of two PET samples revealing the difference between a more crystalline sample exhibiting more trans C —C bonds in the glycol segment (biaxial film) and an amorphous sample rich in gauche C —C bonds (melt) in the spectral range near 286 eV. Figure reproduced from Beamson et al. [10]. Copyright 1996, with permission from Elsevier.

For semicrystalline isotropic materials a qualitative measure of crystallinity is directly obtained from the respective WAXS curve. Figure 8.2 demonstrates the phenomenon for polyethylene terephthalate) (PET). The curve in bold, solid line shows a WAXS curve with many reflections. The material is a PET with high crystallinity. The thin solid line at the bottom shows a compressed image of the corresponding scattering curve from a completely amorphous sample. Compared to the semicrystalline material it only shows two very broad peaks - the so-called first and second order of the amorphous halo. 

It is assumed that the machine background has separately been measured and properly been subtracted under consideration of the absorption factor (Sect. 7.6). In particular it is not allowed to take the diffuse scattering background of a molten or amorphous sample for the machine background. 

PE, the united atom model. We considered a sufficiently long PE chain made up of 5000 united atoms under periodic conditions in each direction. The initial amorphous sample prepared at 600 K was quenched to 100 K and drawn up to 400%. The sample was then quickly heated to various crystallization temperatures, and the molecular processes of fiber formation were monitored in situ via the real-space image and its Fourier transform, the structure function S3d([Pg.79]

Isotropic samples will have no effect on the polarized light no matter how the crystal is oriented, since all crystal axes are completely equivalent. This effect is known as complete or isotropic extinction (Fig. 3a). Noncrystalline, amorphous samples will exhibit the same effect. 

The 2nd-order 300°C rates determined by the Arrhenius equation (Table VI) show that the rates are extremely high compared to the control or boric acid treated samples. In addition, the rate of mass loss appears to be unaffected by crystallinity. Ea values were lowered relative to the untreated control samples, except for the amorphous sample, and also appeared to be unaffected by... 

In systems from which only a polycrystalline or an amorphous sample can be obtained, NMR becomes the method of choice since the diffraction technique requires single crystal samples. 

The quartet spectrum observed for the amorphous samples at temperatures higher than — 70°C. was thought to be caused by rearrangement of radical XVI, giving the radical structure XIX and a chain scission. 

This indicates that even in amorphous samples, in which the uniaxial Ki terms are expected to dominate due to the local distortions from cubic symmetry, there is still a significant contribution from the K4 cubic anisotropy terms. It is interesting to contrast this with the numerical simulations for a-TbFe2 which have shown that the fourth-order anisotropy eneigy per atom was an order of magnitude smaller than the second-order anisotropy energy per atom, albeit that the fourth-order term was of the same order of magnitude... 

Why is it that the maximum modulus of elasticity of crystalline film samples of polycarbonate, even when oriented, does not increase considerably over that of amorphous samples Van Kerpel (19) examined the x-ray diffraction pattern of a crystallized polycarbonate sample held under tension and showed that the crystal lattice of the polycarbonate elongates quite easily in the direction of stretch. He found that the lattice distance (d 2.670 A.) increases to d 2.691 A. and d — 2.714 A. when the polycarbonate film is elongated by 5 and 10%, respectively. 

It was quite unexpectedly found that the amorphous samples of zirconium and hafnium alkoxides M(OR)4 contain several types of oxocomplexes, particularly, M3O(OR)i0 and M40(0R)14 [1612], The trinuclear Zr3([l3-0)()i3-OBu XOBu ), was isolated in a crystalline form and turned out to be a structural analog of the known isopropoxide clusters of Th, Mo, and U(IV) -MjOCOPr ),) [1520] (see also Sections 4.3 and 12.12). The inclusion of the solvent molecules inside the cavities of the structures and formation of alcohol solvates in many cases leads to microanalysis data that does not deviate much from those calculated for M(OR)n. 

The structural types described in Chapt. 4 correspond to the crystalline alkoxides. At the same time, M(OR) are much more prone to give amorphous samples due, supposedly, to the nonhomogeneity of their molecular composition. Crystallization occurs only in the cases when the samples contain only one type of aggregate or a regular polymeric structure. 

Certain information concerning the structure of the oligomeric oxoalkox-ides present in amorphous samples can be obtained regarding the molecular structures of the crystalline oxocomplexes, treating the oxogroups as the knots... 

The major application of Zn(OR)2 is connected with their catalytical activity in the polymerization of olefine oxides. It is rather interesting that the activity of file freshly prepared amorphous samples of the zinc methoxide, ethoxide, or Zn(OMe) (OEt)2.n as heterogeneous catalysts in these reactions is noticeably higher than for soluble R ZnOR >ZnR2 as homogeneous catalysts [808, 1604],... 

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