Crystallinity variation

Crystalline cellulose is believed to exist in at least four crystalline variations. Cellulose I occurs in the majority of plants. Its crystal structure conforms with the diagram in Fig. 75. 

Attention was first drawn to the existence of several crystalline variations of ammonium nitrate by Frankenheim in 1854 [1],... 

In table III, the "crystallinity" variations estimated after multiple irradiations are shown. In spite of the degradation which is clearly noticeable (gradual fading of the weaker interference) the estimated crystallinity often shows very limited decrease (the standard deviations are approximately 8 %). 

Figure 1" shows the crystallinity variation for ZSM-48 and EU-1 zeolites, as a function of the initial... 

Figure 13.6 Examples of correlation between responses from different scales when the interfacial modifier is changed Left, tensile strength at break point (up) and relative crystalline variation for the polypropylene matrix (down) versus the grafting level in the interfacial modifier right, elastic moduli (tensile/DMA) ratio (up) and components of the complex modulus from DMA tests (down) versus the grafting level in the interfacial modifier. (From References 32 and 55 with permission of John Wiley Sons, Inc. and Elsevier, respectively.)...

The most likely cause of the crystallinity variations in polypropylene spherulites is the accumulation of rejected atactic and low molecular weight impurities. This view is supported by the observation that adding increasing amounts of atactic material to polypropylene purified by octane extraction, leads to changes in the crystallinity distribution (Figure U). 

Analysis of these different specimens by X-ray diffraction allows appreciation of the crystalline variation and die extent to which the amorphous components are present (Fig. 22). 

The FTIR method is based on the ratio of certain absorbances [17, 18]. It is especially useful for mapping the crystallinity of surfaces but it is unable to penetrate to any great depth within a sample. Measurement of local crystallinity variations can help assess variation in cooling rate and in the analysis of differential shrinkage and warpage. 

On a part level, molded plastic parts also often have significant variations in the structure of the plastic material in various areas of the parts. There may be areas of high molded-in stress, variations in crystallinity, variations in density, variations in how the polymer molecules are aligned, variations in how additives and reinforcing agents are dispersed, etc. 

Obtaining high-quality nanocry stalline samples is the most important task faced by experimentalists working in tire field of nanoscience. In tire ideal sample, every cluster is crystalline, witli a specific size and shape, and all clusters are identical. Wlrile such unifonnity can be expected from a molecular sample, nanocrystal samples rarely attain tliis level of perfection more typically, tliey consist of a collection of clusters witli a distribution of sizes, shapes and stmctures. In order to evaluate size-dependent properties quantitatively, it is important tliat tire variations between different clusters in a nanocrystal sample be minimized, or, at tire very least, tliat tire range and nature of tire variations be well understood. 

The variation of Cp for crystalline thiazole between 145 and 175°K reveals a marked inflection that has been attributed to a gain in molecular freedom within the crystal lattice. The heat capacity of the liquid phase varies nearly linearly with temperature to 310°K, at which temperature it rises more rapidly. This thermal behavior, which is not uncommon for nitrogen compounds, has been attributed to weak intermolecular association. The remarkable agreement of the third-law ideal-gas entropy at... 

The dissipation factor (the ratio of the energy dissipated to the energy stored per cycle) is affected by the frequency, temperature, crystallinity, and void content of the fabricated stmcture. At certain temperatures and frequencies, the crystalline and amorphous regions become resonant. Because of the molecular vibrations, appHed electrical energy is lost by internal friction within the polymer which results in an increase in the dissipation factor. The dissipation factor peaks for these resins correspond to well-defined transitions, but the magnitude of the variation is minor as compared to other polymers. The low temperature transition at —97° C causes the only meaningful dissipation factor peak. The dissipation factor has a maximum of 10 —10 Hz at RT at high crystallinity (93%) the peak at 10 —10 Hz is absent. 

Gases and vapors permeate FEP resin at a rate that is considerably lower than that of most plastics. Because FEP resins are melt processed, they are void-free and permeation occurs only by molecular diffusion. Variation in crystallinity and density is limited, except in unusual melt-processing conditions. 

There ate three basic technology options for making solar cells with do2ens of variations on each. These approaches ate conveniently grouped as follows thick (- 300 fiTo) crystalline materials, concentrator cells, and thin (- 1 fiva) semiconductor films. 

Subsequent dehydrohalogenation afforded exclusively the desired (Z)-olefin of the PGI2 methyl ester. Conversion to the sodium salt was achieved by treatment with sodium hydroxide. The sodium salt is crystalline and, when protected from atmospheric moisture and carbon dioxide, is indefinitely stable. A variation of this synthesis started with a C-5 acetylenic PGF derivative and used a mercury salt cataly2ed cyclization reaction (219). Although natural PGI has not been identified, the syntheses of both (6R)- and (65)-PGl2, [62777-90-6] and [62770-60-7], respectively, have been described, as has that of PGI3 (104,216). 

Silicates in Solutions. The distribution of sdicate species in aqueous sodium sdicate solutions has long been of interest because of the wide variations in properties that these solutions exhibit with different moduli (23—25). Early work led to a dual-nature description of sdicates as solutions composed of hydroxide ions, sodium ions, coUoidal sdicic acid, and so-called crystaHoidal sdica (26). CrystaHoidal sdica was assumed to be analogous to the simple species then thought to be the components of crystalline sdicate compounds. These include charged aggregates of unit sdicate stmctures and sdica (ionic micelles), and weU-defined sdicate anions. 

Milling not only provides intimate mixing, but also eliminates variation in ribbon thickness and cmshes lumpy materials, eg, overdried soap, which might impact finished bar texture. Milling is also used for the formation of the proper bar soap crystalline phase, which plays a critical role in both the performance properties of the soap bar and the handling characteristics of the in-process soap. For example, too hot a milling temperature can create sticky soap that is difficult to process further. 

There are many variations on crystalline cane sugar from refineries, in addition to the direct production and noncentrifugal sugars described above. 

The pursuit of further miniaturization of electronic circuits has made submicrometer resolution Hthography a cmcial element in future computer engineering. LB films have long been considered potential candidates for resist appHcations, because conventional spin-coated photoresist materials have large pinhole densities and variations of thickness. In contrast, LB films are two-dimensional, layered, crystalline soHds that provide high control of film thickness and are impermeable to plasma down to a thickness of 40 nm (46). The electron beam polymerization of CO-tricosenoic acid monolayers has been mentioned. Another monomeric amphiphile used in an attempt to develop electron-beam-resist materials is a-octadecylacryUc acid (8). 

Riboflavin forms fine yellow to orange-yeUow needles with a bitter taste from 2 N acetic acid, alcohol, water, or pyridine. It melts with decomposition at 278—279°C (darkens at ca 240°C). The solubihty of riboflavin in water is 10—13 mg/100 mL at 25—27.5°C, and in absolute ethanol 4.5 mg/100 mL at 27.5°C it is slightly soluble in amyl alcohol, cyclohexanol, benzyl alcohol, amyl acetate, and phenol, but insoluble in ether, chloroform, acetone, and benzene. It is very soluble in dilute alkah, but these solutions are unstable. Various polymorphic crystalline forms of riboflavin exhibit variations in physical properties. In aqueous nicotinamide solution at pH 5, solubihty increases from 0.1 to 2.5% as the nicotinamide concentration increases from 5 to 50% (9). 

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