Crystal thickness annealing

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

Annealing drawn PE hydrostatically at high pressure, generates a wide spectrum of crystal thicknesses varying from the common oriented chain folded to the chain-extended structures — where folds and ties tend to disappear63 —. This range of crystal thicknesses coupled with the chain axis orientation, offers a suitable model in... 

Raman spectral-band frequencies for poly (thietane) as a crystallized melt annealed at 62° satisfy the rules for a longitudinal acoustic-mode frequency for deducing thickness. The morphology and physical properties of isoprene thietane block copolymers have been studied. Potential energies have been calculated for helical- and glide-type conformations of poly (thietane), and the conformations of the homopolymer have been calculated. ... 

Table 6.9 Long Period L (nm), Lamellar Thickness 1 (nm), and Amorphous Interlamellar Thickness /a (nm) of Pure iPP and iPP/HOCP Blends Isothermally Crystallized and Annealed.

In the following figures, further experiments are linked to the annealing and recrystallization of a number of additional polymers. In Fig. 6.81 the increase of lamellar thickness is illustrated on the example of solution-grown polyethylene. The crystals were collected in dried mats. The graph on the right side allows a comparison with data on melt-crystallized and annealed polyethylene (see also Sect. 5.2). Sufficiently mobile and flexible molecules, such as polyethylene, can thicken by chain... 

A Knudsen oven and quartz crystal thickness monitor have been attached to a HPLP system, enabling accurate, reproducible dosing of submonolayer quantities of gold under the ultraclean conditions of the UHV chamber. Results indicate that atoms of gold inhibit the catalytic activity of the platinum in heptane isomerization. However, annealing to form a 2-D alloy (and the consequent separation of surface platinum into small ensembles), actually led to an increase in isomerization activity over the dean platinum value. 

The parting compound C, see Fig. 4.24 avoids the separation of the crystal layer through crystal thicknesses < 0.4 mm. With an optimum annealing procedure the critical stress values are not reached before room temperature. 

Crystallite size depends very strongly on the temperature of crystallization and annealing. Its thickness can be determined from small-angle X-ray scattering [137-139], electron microscopy, and from the analysis of the Raman low frequency longitudinal mode [140-142]. These methods allow also the determination of the crystallite size distribution [139, 142, 143]. 

The lamellar thicknesses after solution crystallization and annealing at different temperatures showed a decrease with decreasing syndiotacticity index and annealing temperatures. The long spacings are also critically dependent upon the solvent systems used in solution crystallization. It was postulated that defects might be included, at least to a certain degree, in the crystal lattice. 

They were measured using samples of rather well defined texture. The first measurements performed on polyethylene samples with fiber texture subjected to annealing at high pressure for increasing the crystal thickness yielded a critical shear stress of 11.2 MPa for undisclosed crystal thickness [84]. However,... 

Fig. 1. Distribution of X centers (ocjf) and F centers (Np) from the surface of a colored KCl crystal after annealing. Original thickness was 2.44 mm.

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