Crystal region

Increased crystallinity can reduce permeabiHty values because the crystal regions of a polymer are impenetrable ia most semicrystaUine polymers. Hence, the average value of the solubiHty coefficient S is reduced. It also means that movement must occur around the crystaUites, which means that a longer distance must be traveled. This lowers the effective value of D. 

Fig. 18.1 Melting temperature (squares) and temperature of crystallization (triangles) for CZX-1 as a function of the DSC cooling rate. A plateau in the crystallization temperature is observed for cooling rates below l°/min resulting in a no-crystallization region of about 15°.

For the smaller particles which Include only a few tens or hundreds of atoms, any twinning or faulting reduces the range of ordering to the extent that the pattern can not be Interpreted In the same way as a pattern from an extended crystal. The Individual single-crystal regions may contain only two or three atomic planes. Interpretation can be made only by calculation of patterns from postulated models for the configurations of atoms (22). 

The powder patterns obtained by X-ray diffraction and selected area electron diffraction do represent averages over very large numbers of particles but the averaging over size, orientation and imperfection of crystals removes much of the important information, especially that on the correlations of properties,e.g, the orientational relationship of adjacent crystal regions or the dependence of twinning on size. 

The DLAM frequency of random copolymers of ethylene behaves in a different manner [103]. For these copolymers ethyl and longer branches are excluded from the crystal region. The branches accumulate in the interlamellar... 

It has recently been shown (7) that a transformation from fibrillar to lamellar morphology is not required to replicate the force-temperature profile of stretched networks in the crystallization region. This latest work shows that a close duplication of the behavior of gutta percha (8) can be predicted with a model (7) of fibrillar crystallization that Incorporates several new features omitted in earlier theories, specifically ... 

For particles in the 1-2 nm size range this situation is in some respects simpler but in other respects more difficult. Nanodiffraction patterns can be obtained from regions encompassing the whole particle so that evidence should be provided on the orientations and interrelations of all single crystal regions that are present. 

A further point is that for a multiply-twinned particle of diameter 1 nm, for example, the constituent single crystal regions are half of this size or less and so contain only two or three planes of atoms. One can not expect, under these circumstances, that the diffraction pattern will be made up merely by addition of the intensities of the single crystal regions. Coherence interference effects from atoms in adjacent regions will become important. It is then necessary to compare the experimental patterns with patterns calculated for various model structures. 

Structure refinement based on dynamical scattering was developed by Zandbergen and Jansen (Zandbergen et al, 1997 Jansen et al, 1998), known as the MSLS software. Electron diffraction from crystal regions with relatively homogenous thicknesses was used. Both the crystal orientation, crystal thickness and the atomic coordinates could be refined simultaneously. 

Figure 1.67 Specific volume as a function of temperature on cooling from the melt for a polymer that tends to crystallize. Region A is liquid, B liquid with elastic response, C supercooled liquid, D glass, E crystallites in a supercooled liquid matrix, F crystallites in a glassy matrix, and G completely crystalline. Paths ABCD, ABEF, and ABG represent fast, intermediate, and very slow cooling rates, respectively. From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Fig. 8. Comparison of experimental phase boundary concentrations between the biphasic and liquid crystal regions for various liquid crystalline polymer solutions with the scaled particle theory for hard wormlike spherocylinders. The symbols are the same as those in Fig. 7...

Thermal uniformity in the cold zone was found to be from 0.01 to 0.02 °C, and that in the hot zone was found to be better than + 0.5 °C vertically and + 0.1 °C horizontally. Thermal gradients near the solid-liquid interface were achieved in excess of 30 °C cm " in the crystal region and up to 20 °C cm" in the melt. The growth of crystals was performed in a sealed transparent silica ampoule, which has two rooms for As source and GaAs polycrystalline, respectively, separated by a quartz diffusion barrier. For details of the growth process the reader is referred to Ref. 43. In this experiment the As source temperature T. was systematically reduced by 2 °C at 3 h intervals from 620 °C to 614 °C. 

Solution. As usual, take the boundary as a slab that is 5 thick. In considering diffusion along the tilt axis, any contribution of the crystal regions in the slab can be neglected and only the contributions of the dislocation pipes are included because D° DXL. The flux through a unit cross-sectional area of the boundary slab is then... 

Glass No. Hk measured Hk calculated AHk (Hk mens Kcalc) Initial crystallization region... 

Mullin (1993, p. 117) describes the crystallization regions in Figure 3.4a as the following ... 

The pattern obtained by heating a copper crystal in oxygen at atmospheric pressure at 250° is shown in Fig. 1. The different crystal regions can be identified from the symmetry of the pattern. 

Each detector 14 includes a detector crystal region 21 having a junction 22 which is connected to an indium bump 23. The indium bump bonds to the bonding pad 80 which is, in turn, bonded to a metallized trace 13. The sensitive area plane 12 is parallel to the plane formed by the edge of the supporting substrate and the multilayer thick/thin film interconnect pattern 50. 

The middle diagram of Figure 11 illustrates phase behavior that may be more desirable for some applications. In this case the presence of a lamellar liquid crystal region in the phase diagram, although it will not be revealed by experiments confined to low surfactant concentrations, may be exploitable for the formation of very stable dispersions (82). 

All these heat capacity and enthalpy studies do not conclusively define the temperature dependence of the heat capacity of liquid zinc. In addition, some of these heat capacity and enthalpy studies (3, 4, 7) do not show good agreement with the adopted values In the crystal region. However, the adopted constant value Is consistent with the experimental data (within the uncertainty of the data) and with the vaporization data. The literature survey for Zn was done In part by Hultgren (8). 

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