Melt-quenched phase

First, let s examine the case of sPS [12]. Figure 14 shows the FT-IR spectra of this polymer the lower and upper parts of the figure are the spectra for samples, melt-quenched and annealed at 120 °C for 400 min, respectively. The latter shows that the crystal form is a phase with an all-trans conformation [56,57]. As seen from this figure, several absorption bands at 538, 935, 1224, and 1335 cm-1 vary with annealing or crystallization. Of these, the band at 1224 cm-1 was assigned to the crystalline packing, and some bands around 538 cm-1 were related to the conformational changes by Kobayashi et al. [56]. 

Continuous laser melt quenching of hypoeutectic Ag-Cu alloys has been performed and discussed by Copley et al. (1995) nano-phase coupled growth structures (with spacing of 10 nm) have been observed in banded nano-structures. 

The vapour deposition method is widely used to obtain amorphous solids. In this technique, atoms, molecules or ions of the substance (in dilute vapour phase) are deposited on to a substrate maintained at a low temperature. Most vapour-deposited amorphous materials crystallize on heating, but some of them exhibit an intervening second-order transition (akin to the glass transition). Amorphous solid water and methanol show such transitions. The structural features of vapour-deposited amorphous solids are comparable to those of glasses of the same materials prepared by melt-quenching. 

Sometimes, small structural differences in morphology of polymer samples can be isolated by using a double subtraction technique. For example, with polyethylene terephthalate) PET, differences in the amorphous phase of the melt-quenched polymer and solution-cast polymer can be isolated by first subtracting out the contribution due to the trans isomer and then subtracting the two difference spectra from each other 214). (Fig. 16) shows the resultingdifference spectrum obtained after the second subtraction. Obviously the two amorphous structures are different from each other. 

Amorphous phases are attractive to study mechanisms of cocrystal formation because they require very small samples (3-5 mg) and can be prepared and studied in situ (by melt-quenching) in a calorimeter or on a microscope stage. Cocrystallization pathways can then be identified and kinetics measured from the analysis of thermal events, photomicrographs and spectroscopic analysis in real time. An example of the cocrystallization of CBZ NCT from an amorphous film of equimolar composition of reactants is shown in Fig. 24. 

It has been well known for a couple of decades that noncrystalline metallic alloys can be made by vapour- and melt-quenching. Recent results show that an amorphous phase can also be formed directly when a crystalline metallic alloy is subjected to various types of disordering processes. Solid-state amorphization can be induced through a variety of methods including absorption of atomic hydrogen, thermal interdiffusion reaction along the interface separating... 

It is known that polyoxymethylene in the crystalline phase takes the all gauche conformation with a 9/5 helix [21]. However, the amorphous phase has a distribution of gauche and frans-conformations. Figures 7.10 and 7.11 show the CPMAS NMR spectra and powder pattern spectra of polyoxymethylene, respectively [22]. Sample A is a polyoxymethylene single crystal. To produce Sample B, Sample A is heated to 200°C and then quenched in ice water. Sample C is a melt-quenched sample of bulk polyoxymethylene and sample D is a bulk polyoxymethylene heated and cooled at a rate of... 

As will be apparent in Chapter 4, MD simulations have made major contributions to our understanding of the structures and dynamical properties of solids. Problems and processes simulated include phase transitions (e.g. Impey et al., 1985 Meyer and Ciccotti, 1985), orientation dynamics in molecular crystals (e.g. Dove and Pawley, 1984) and ionic and diffusion (e.g. Gillan and Dixon, 1980 Vashishta and Rahman, 1978). In addition, they have been used to study melting and, as noted above, to prepare glass structures by a simulated melt-quench cycle as described by Vessal in Chapter 12. 

Ino] Inoue, A., Harakawa, Y., Oguehi, M., Masumoto, T., Metastable MC Phase in Melt-Quenched C-Fe-V and Fe-C-V-(Cr or Mo) Alloys-Mechanical Properties and Powder-Forming Tendency by Comminution , J. Mater. Sci., 21, 1310-1320 (1986) (Crys. Structure, Morphology, Phase Relations, Experimental, Meehan. Prop., 16)... 

Experiments of this type have been carried out on partially deuterated polystyrenes (using quenched phases from the melt) by J. P. G>tton and co-workers. These experiments give us precise information oil the local correlations between chains in a polymer melt. Also, because of the simplicity introduced by the Flory theorem, this is one of the few cases where the scattering diagrams can be computed accurately. The method is described in Chapter X. Here we present the results only, in qualitative terms. 

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