Crystallization kinetic orders, examples

A number of systems which in polymer literature are normally referred to as mesophases are obtained under kinetic control. Examples are the smectic phase of isotactic polypropylene [18,19], mesomorphic syndiotac-tic polypropylene [20-22], mesomorphic PET [23,24], and other instances where intermediate degrees of order result after quenching polymers from the melt to temperatures often close to Tg. In these cases disorder is plausibly more static than in bundles close to T0 and these phases usually crystallize upon heating to an appropriate temperature in the stable crystal phases. 

The approach used in this example case study is to obtain the kinetic order i from laboratory data. Since i is "system specific," It should not change with scale, If one reliable set of crystal size distribution data at a known residence time is available from plant operation, then B° and C can be extracted after the data are convened to population density. Knowing B°, G. and i, kN is computed easily using Eq. (11,3-15). Note In this devetopmeal, the solid concentration Mr is assumed constant. 

A polymorph of the quinoid red crystal form of fluorescein was one of the first examples of a complex molecule whose structure was determined by a real space approach based on the Monte-Carlo method. The same method has more recently been used to solve the structure of the (3-form of the latent pigment boc-DPP (Figure 8-6). The kinetics of the thermal fragmentation to DPP differs for both forms. The more reactive a-form crystallizes (less ordered) with three conformation-ally different half-molecules in the asymmetric unit. This structure was initially solved from single crystal data. However, it could be improved substantially by Rietveld refinement, thus demonstrating the potential of this technique . ... 

This section has shown examples of how through MD isolation and confinement, which typically results from the self-assembly of block copolymers, crystalline phases can change their nucleation behavior from heterogeneous to superficial, or homogeneous nucleation and their crystallization kinetics can also change from a complex process to a simple first-order process dominated by nucleation. Intermediate behavior is common, when percolated and isolated phases coexist. In many cases fractionated crystallization can be found as well as fractionated melting (although this last case has only been documented once for nanometric PEO droplets within PB-/ -PEO or PE-fo-PEO as presented above). 

In this section the crystallization kinetics of blends whose components are miscible in some proportion in the melt will be discussed. In such partially miscible systems, liquid-liquid phase separation could intervene and influence the crystallization process. Therefore, in order to properly analyze the crystallization kinetics in such systems it is necessary that the phase diagram be established. These systems represent a classical example where the melt structure plays an important role in governing the ensuing crystallization. The reason for this requirement will become clear as some typical phase diagrams, involving a crystallizable polymer, are examined. 

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