Amorphous state studies

Questions of interest to amorphous state studies include the design of critical experiments concerning the shape of the polymer chain, the estimation of type and extent of order or disorder, and the development of models suitable for physical and mechanical applications. It must be emphasized that our knowledge of the amorphous state remains very incomplete, and that this and other areas of polymer science are the subjects of intensive research at this time. Pechhold and Grossmann (4) capture the spirit of the times exactly ... 

In the studies that attribute the boundary friction to confined liquid, on the other hand, the interests are mostly in understanding the role of the spatial arrangement of lubricant molecules, e.g., the molecular ordering and transitions among solid, liquid, and amorphous states. It has been proposed in the models of confined liquid, for example, that a periodic phase transition of lubricant between frozen and melting states, which can be detected in the process of sliding, is responsible for the occurrence of the stick-slip motions, but this model is unable to explain how the chemical natures of lubricant molecules would change the performance of boundary lubrication. 

The results of the XRD measurement showed that the Fe jAl, jPO catalyst was almost in amorphous state. Only a very broad peak at 29 of ca. 23 degree was observed. The Mossbauer spectroscopic study on this catalyst showed one doublet of iron with the isomeric shift of 0.31 mm s (a-Fe was used as the reference) and the quadrupole splitting of 0.62 mm s. These parameters are very close to those observed for FePO [13, 14], suggesting that the iron cation in the catalyst is tetrahedrally coordinated with oxygen and isolated by four PO tetrahedral units. Such coordination circumstance was suggested to be a key factor for the iron site effective for the oxidation of CH to CHjOH by H -Oj gas mixture [15]. 

Finally, we were led to the last stage of research where we treated the crystallization from the melt in multiple chain systems [22-24]. In most cases, we considered relatively short chains made of 100 beads they were designed to be mobile and slightly stiff to accelerate crystallization. We could then observe the steady-state growth of chain-folded lamellae, and we discussed the growth rate vs. crystallization temperature. We also examined the molecular trajectories at the growth front. In addition, we also studied the spontaneous formation of fiber structures from an oriented amorphous state [25]. In this chapter of the book, we review our researches, which have been performed over the last seven years. We want to emphasize the potential power of the molecular simulation in the studies of polymer crystallization. 

II, and III), two were monohydrates (termed a-monohydrate and /3-monohydrate) and one was a ferf-butylamine disolvate. The differences in the powder patterns of the phases were readily evident (Table 1). This study demonstrates the unique ability of x-ray diffractometry for the identification of (1) anhydrous compound existing in both crystalline and amorphous states, (2) different polymorphic forms of the anhydrate, (3) the existence of solvates where the solvent of crystallization is water (hydrate) or an organic solvent (in this case, /m-butylamine), and (4) polymorphism in the hydrate. 

Spiro-shaped HTMs have been studied extensively (Scheme 3.16) [88,89], The introduction of a spiro center improves the thermal stability of the amorphous state without significantly changing charge-transport properties. Compared with using NPD, TPD HTMs, using 43 in ITO/HTM/Alq3/LiF/Al devices showed very high luminescent efficiency [90]. 

Packing efficiency can also be described by the extent of short-range order in the amorphous state. Mitchell has shown through X-ray scattering studies that, while the local molecular organization of noncrystalline polymers is random, in many cases, there are additional correlations that do not perturb the chain trajectory but will impact polymer properties.15 These correlations have a limited spatial range (<50A) but will have a particular impact on bulk properties... 

In general, the miscibility between two polymers can be predicted by thermal characterization of the blends [36], One of the most simple and effective ways to predict miscibility between two polymers is to consider the behavior of the glass transition temperature in the blend systems, which is known as the Tg method. In miscible blend systems, only a single 7 g intermediate between two components appears in the amorphous state. Therefore, we studied the change of... 

Only with silica was the nature of the surface groups studied as extensively as with carbon. Silica, like carbon, has several polymorphs. Apart from the amorphous state, it is known to exist in numerous crystalline modifications. The most important forms are quartz, tridymite, and cristobalite. Each of these can occur in a low-temperature form and in a high-temperature form of somewhat higher symmetry. Tridymite is only stable if small amounts of alkali ions are present in the lattice 159). Ar. Weiss and Al. Weiss 160) discovered an unstable fibrous modification with the SiSj structure. Recently, a few high-pressure modifications have been synthesized keatite 161), coesite 162), and stishovite 16S). The high-pressure forms have been found in nature in impact craters of meteorites, e.g., in the Arizona crater or in the Ries near Nbrdlingen (Bavaria). 

The method of complex study of magnetic effects and the changes of electron diffraction patterns during the heating of amorphous alloys is developed. The study was carried out on the alloys Fe-Si-B, that were the bands in amorphous state. The phase composition that correspond to registrated diffraction patterns and to magnetic effects is established. 

The amorphous state of the lyophilized solids was verified by powder X-ray diffractometry (Rigaku Denki Co., Ltd., Danvers, MA), and their Ca/P04 ratios after dissolution in HCl were determined by atomic absorption (AAS, Perkin Elmer, Norwalk, CT) and UV spectrophotometric [6] (Varian Analytical Instruments, Palo Alto, CA) measurements of Ca + and PO4, respectively. Dissolution of the ACP fillers was studied by kinetically following the changes in Ca + and PO4 concentrations in continuously stirred HEPES-buffered (pH = 7.4) solutions adjusted to 240 mOsm/kg with NaCl at 37°C. All solutions initially contained 0.8 mg/mL of the ACP filler. 

Studies of the model compounds III and IV 33) and others 39) have shown that the NH-groups take part in hydrogen bonding both in the crystalline and amorphous states not only as electron donors but also as electron acceptors. Table 4 presents thermodynamic parameters for a series of model complexes. 

Structural study of polysaccharides and other carbohydrates in solution or in the amorphous state has been significantly enhanced through the application of Fourier-transform, infrared spectroscopy. Among the advantages of this method may be mentioned the high quality of the spectra, and the in-house ability to interact with the computer, so that the digitized spectra may be stored and manipulated in such a way that additional information is obtained. The application of F.t.-i.r. spectroscopy in the field of carbohydrate chemistry and biochemistry is still in its infancy,182 but... 

VIII. Calorimetric Studies of the Amorphous State and of the Glass Transitions 252... 

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