Nucleation random

As we describe later complex metal hydride thin films can also be made in situ by M B D using an atomic hydrogen source. As a result of their different microstmeture, these films nucleate randomly on rehydrogenation. 

Improved clarity of PP has provided the ability for replacement of PVC with PP in applications such as blisterpacks for hardware. In addition, new PP resins are being developed that use single-site metallocene catalysts (mPP). While virtually no difference exists in the processing behavior or finished product properties between conventional PP and mPP, these new materials are easier to nucleate. The use of nucleated mPP provides for a product with the higher physical properties of PP homopolymer and the clarity of nucleated random PP copolymer. 

Sterzynski, T., Lambla, M., Crozier, H. and Thomas, M. (1994) Structure and properties of nucleated random and block copolymers of polypropylene, Adv. Polymer Technol, 13, 25. 

A Brabender DSK 42/6D twin-screw extruder was used for the preparation of p-nucleated homopolymer Mosten 58412 (B-PP-H) and P-nucleated random... 

Samples can be concentrated beyond tire glass transition. If tliis is done quickly enough to prevent crystallization, tliis ultimately leads to a random close-packed stmcture, witli a volume fraction (j) 0.64. Close-packed stmctures, such as fee, have a maximum packing density of (]) p = 0.74. The crystallization kinetics are strongly concentration dependent. The nucleation rate is fastest near tire melting concentration. On increasing concentration, tire nucleation process is arrested. This has been found to occur at tire glass transition [82]. 

Nucleation is assumed to begin simultaneously from centers positioned at random throughout the liquid. This is more descriptive of heterogeneous nucleation by foreign bodies introduced at a given moment than of random nucleation. We shall dispense with the requirement of simultaneity below. 

Fig. 7.4. Heterogeneous nucleation takes place at higher temperatures because the maximum random fluctuation of 10 atoms gives a bigger crystal radius if the atoms are arranged as a spherical cap.

In this chapter we have shown that diffusive transformations can only take place if nuclei of the new phase can form to begin with. Nuclei form because random atomic vibrations are continually making tiny crystals of the new phase and if the temperature is low enough these tiny crystals are thermodynamically stable and will grow. In homogeneous nucleation the nuclei form as spheres within the bulk of the material. In... 

Now, nucleation at 910°C will only take place if we get a random fluctuation of about 10 atoms (which is the maximum fluctuation that we can expect in practice). Nucleation... 

Homogeneous nucleation occurs when, as a result of statistically random segmental motion, a few segments have adopted the same conformation as they would have in a crystallite. At one time it was considered that the likelihood of the formation of such nuclei was greatest just above the transition temperature... 

Alzheimer s Disease. Figure 1 A(3 monomers can self-associate to form dimers, trimers and higher oligomers. Globular structures of synthetic A(342 are known as A(3-derived diffusible ligands (ADDLs) (3-12-mers of A(3). These structures are similar to the smallest protofibrils and represent the earliest macromolecular assembly of synthetic A(3. The characteristic amyloid fiber exhibits a high beta-sheet content and is derived in vitro by a nucleation-dependent self-association and an associated conformational transition from random to beta-sheet conformation of the A(3 molecule. Intermediate protofibrils in turn self-associate to form mature fibers. 

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