Bulk amorphous + crystalline

In the 1970s a model for semi-crystalline polymers was presented by Struik (1978) it is reproduced here as Fig. 2.13. The main feature of this model is that the crystalline regions disturb the amorphous phase and reduce its segmental mobility. This reduction is at its maximum in the immediate vicinity of the crystallites at large distances from the crystallites will the properties of the amorphous phase become equal to those of the bulk amorphous material. This model is similar to that of filled rubbers in which the carbon black particles restrict the mobility of parts of the rubbery phase (Smith, 1966). 

Post-failure studies of the fracture surface morphology of bulk semi-crystalline polymers are more difficult than those of amorphous materials due to the more complex multiphase structure associated with semi-crystalline materials However, it was shown that some fractographic details point to the formation of a stress whitened region ahead of a notch prior to final fracture of the material. In particular, stress-whitened regions were easily visible in semi-crystalline polymers such as LDPE and HDPE The resulting, macroscopically apparently brittle fracture... 

For simulating the heterogeneous crystallization process, a test specimen witii a dimension of 3a 3a l2a including two amorphous-crystalline interfaces is prepared by attaching 12 layers of c-Si (216 atoms), as a crystalline seed, to a bulk fl-Si (648 atoms). The bulk a-Si is obtained by the above cooling process and pre-annealed at 500 K for 200 ps. The constant NVT MD simulations are carried out using the Newton equation with a time step for the integration set at 2fs. 

It is well known that HjO molecules are able to condense into a wide variety of solid phases. Apart from crystalline structures, two forms of bulk amorphous... 

As discussed in the sections on individual polymers, PEO is a semicrystalline polymer with about 60% of the bulk being crystalline at room temperature with the rest being present in an amorphous phase. In spite of the difficulties involved in obtaining phase diagrams with polymer electrolytes such as the slow kinetics of crystallization and randomness and therefore to determine exact boundaries between the various phases involved, phase diagram studies on PEO system suggests 3-4 repeat units of PEO per metal salt (vide supra) [53-56]. 

The mechanisms of plastic deformation at microscopic level of amorphous polymers are mainly crazing and shear yielding [3-5]. In semicrystalline polymers, although the glass transition temperature, density, infrared spectrum and other properties of the amorphous phase interdispersed between the crystalline lamellae are close to those of bulk amorphous polymers, the mechanisms of plastic deformation are very different from those of the amorphous materials, since also the crystalline phase plays a key role [Ij. However, because of the presence of the entangled amorphous phase, the mechanisms of plastic deformation of semicrystalline polymers are also different from those of other crystalline materials (for instance metals). 

The construction of a condensed phase that is representative of a bulk amorphous material consisting of one or more molecules that have been built as described above requires that the molecules be packed in a container so as to enforce a predetermined density on the system. If the system is monoatomic, ie, is a nobel gas, the atoms are inserted one at a time in the box with evaluation of the energy at each attempted insertion. Those trials with too great an energy according to some criterion, most preferably the Metropolis Monte Carlo criterion (93) to be discussed, are discarded. Successive attempts to place atoms in the box are continued imtil the required density has been achieved. Of course, in this simple case it may be preferable to start with an easily constructed crystalline array and then randomize it by the molecular dynamics or Monte Carlo techniques to be described. 

Synthesis of Ni-based bulk amorphous alloys by warm extrusion of amorphous powders. Journal of Non-Crystalline Solids, Vol. 315, No. 1-2, (January 2003), pp. 89-96, ISSN 0022-3093... 

Last, one should not neglect the very simple but all important density. The crystalline cell is usually about 10% more dense than the bulk amorphous polymer. Significant deviations from this density must mean an incorrect model. 

In order to investigate the deformation properties and mechanical memory, it is of interest to study the behavior of polymer fine particles while in an applied external force. One of the experimentally obtained values of those properties is known as Young s modulus, which is a ftmdamental measure of the stiffness of a material. Numerous calculations have been performed for the mechanical property of bulk-like crystalline PE polymer using force field [187-190] semi-empirical [236], ab initio calculation [237,238],and ab initio MD methods [239,240]., We have calculated the compressive (bulk) modulus for the amorphous PE particles using MD with an external force as shown in Fig. 19. At the start, a plate treated as a continuous wall is set at 10 A from the closest atom of the particle in... 

The long period, the crystalline and amorphous layer thicknesses and the bulk volume crystallinity were obtained from an analysis of the correlation functions, an example is shown in Fig. 7.12b. The correlation function is defined as ... 

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