Crystalline-amorphous features determinants

In comparing the shear fracture surfaces of amorphous and semi-crystalline polymers, it appears that the features in both cases are quite similar (Fig. 39a -c ). This indicates that, under comparable conditions, the local stress field rather than details of the crystalline-amorphous microstructure of the polymers tested determines the operating deformation mechanism. Only secondary effects arise from the morphology of the cry stalline material. 

In a discussion of these results, Bertrand et al. [596,1258] point out that S—T behaviour is not a specific feature of any restricted group of hydrates and is not determined by the nature of the residual phase, since it occurs in dehydrations which yield products that are amorphous or crystalline and anhydrous or lower hydrates. Reactions may be controlled by interface or diffusion processes. The magnitudes of S—T effects observed in different systems are not markedly different, which indicates that the controlling factor is relatively insensitive to the chemical properties of the reactant. From these observations, it is concluded that S—T behaviour is determined by heat and gas diffusion at the microdomain level, the highly localized departures from equilibrium are not, however, readily investigated experimentally. 

Wide angle X-ray diffraction, WAXD, studies on the PHAs from octanoic acid (PHA-OCT), nonanoic acid (PHA-NON), and decanoic acid (PHA-DEC) showed that these polymers had the same features as synthetic comb-like polymers [54]. PHA-OCT is the most crystalline (AHm = 8.3 cal/g) and PHA-HEX (the PHA from hexanoic acid) is amorphous, while PHA-HEP (the PHA from hep-tanoic acid) has a very low degree of crystallinity (AHm= 1.3 cal/g). The degrees of crystallinity of PHA-OCT and PHA-NON were determined to be 20 and 30%,... 

The edge position is not always quantitatively informative. The edge features of 3d elements, which are pronounced in crystalline compounds, are blurred in the amorphous or highly dispersed state, probably because of mixing of various symmetries. This renders determination of the oxidation state by comparison with edge positions in crystals troublesome. The position of the pre-peak gives more reliable information when the final state... 

The intention of this brief survey has been to demonstrate that besides the "classical" aspects of isotropic polymer solutions and the amorphous or partially crystalline state of polymers, a broad variety of anisotropic structures exist, which can be induced by definable primary structures of the macromolecules. Rigid rod-like macromolecules give rise to nematic or smectic organization, while amphiphilic monomer units or amphiphilic and incompatible chain segments cause ordered micellar-like aggregation in solution or bulk. The outstanding features of these systems are determined by their super-molecular structure rather than by the chemistry of the macromolecules. The anisotropic phase structures or ordered incompatible microphases offer new properties and aspects for application. 

By comparing die observed spectra with spectra measured in die laboratory, one can determine the crystallinity of icy grains [3]. For Elias 16 (a molecular cloud), the observed feature around 3 pm fits die spectrum of amorphous ice at... 

Micro-Raman spectroscopy was used to characterise 4H-SiC layers grown from a variety of precursor systems.381 FTIR data were able to characterise hydrogenated amorphous silicon nitride films with embedded nanoparticles. Oxidation leads to the appearance of an Si O feature at 1070 cm 1,382 Raman spectra were used to determine the degree of micro-crystallinity of pc Si I I layers, using the intensity ratio of bands at 520 cm-1 and 480 cm-1.383 IR and Raman spectra were used to determine the effects of neutron irradiation on a-SiC H films.384 A range of a-SiCx I I and a-SiCxNy H films were studied using IR spectroscopy 385 similar experiments were carried out on a-Si i xGcx Il,F films.386... 

The residual difference after a successful DDM refinement or/and decomposition can be considered as a scattering component of the powder pattern free of Bragg diffraction. The separation of this component would facilitate the analysis of the amorphous fraction of the sample, the radial distribution function of the non-crystalline scatterers, the thermal diffuse scattering properties and other non-Bragg features of powder patterns. The background-independent profile treatment can be especially desirable in quantitative phase analysis when amorphous admixtures must be accounted for. Further extensions of DDM may involve Bayesian probability theory, which has been utilized efficiently in background estimation procedures and Rietveld refinement in the presence of impurities.DDM will also be useful at the initial steps of powder diffraction structure determination when the structure model is absent and the background line cannot be determined correctly. The direct space search methods of structure solution, in particular, may efficiently utilize DDM. 

It should be emphasized that all of the crystalline polymers discussed here are not totally crystalline but partly crystalline and partly amorphous. Thus one expects to see behavior characteristic of the crystalline regions superposed upon behavior characteristic of the amorphous regions. This superposition is not necessarily a linear one but may rather be a complex coupling of the response of each region. Furthermore, the degree of crystallinity as well as the crystallite size is not a unique feature of any polymer system. Both of these properties are determined by prior thermal history. 

An interesting feature of XANES for structure determination in condensed matter is that it can be used to study the local structure both in crystalline and disordered materials. Therefore once a local structure has been solved for a crystalline material also the similar structure in amorphous, liquid or complex materials, where diffraction methods cannot be applied, can be solved. 

Structural features of cellulosic materials that determine their susceptibility to enzymatic degradation include (1) the moisture content of the fiber (2) the size and diffusibility of the enzyme molecules involved in relation to the size and surface properties of the gross capillaries, and the spaces between microfibrils and the cellulose molecules in the amorphous regions (3) the degree of crystallinity of the cellulose (4) its unit-cell dimensions (5) the conformation and steric rigidity of the anhydroglucose units (6) the degree of polymerization of the cellulose ... 

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