Lamellar crystallization

This intensity can be used to calculate the correlation fiinction (Bl.9.101) and the interface distribution fiinction (B 1.9.102) and to yield the lamellar crystal and amorphous layer thicknesses along the fibre. 

Significant amounts of comonomer also reduce the abiUty of the polymer to form lamellar crystals from solution. In some cases, the polymer merely gels the solution as it precipitates rather than forming distinct crystals. At somewhat higher VDC content, it may precipitate in the form of aggregated, ill-defined particles and clusters. 

The dichloride 8.21a forms fragile, lamellar crystals with a golden colour. The X-ray structure reveals a layered arrangement of hexameric units formed by linking three ( BuNTeCl2)2 dimers by chloride bridges. The reaction of 8.21a with potassium tert-butoxide yields... 

Fig. 17. Schematic representation of the sup-ramolecular structure of polymers containing lamellar crystals...

Fig. 18a-c. Schematic representation of ECC melting under isometric conditions (a), of ECC melting if samples are allowed to shrink during melting (b), of melting of a lamellar crystal (c)... 

A different approach [23, 32] considers AF in Eq. (2.2) to consist of a part which must be defined with respect to infinite chain length plus an entropy of localization [33] due to the pairing of chain ends which becomes important in the case of closely stacked lamellar crystals [34]. It amounts to — Kin (Cp) per molecule, where C is a constant related to the flexibility of the chains in the melt, and which arises due to the conformations of the finite chain. Hence ... 

Figure 9.22. Scanning force microscopy images of polyethylene films formed on a model planar chromium polymerization catalyst. The small white stripes are lamellar crystals. These form the well-known spherulite superstructure upon crystallization from the...

One of the most remarkable features of polymer crystallization is that such chain molecules can form lamellar crystals that contain heavily folded polymer chains. In experiments, the structural analysis of these lamellar crystals became possible when polyethylene single crystals were first prepared from a solution [100-102]. It was found that the orientation of the polymer chains... 

The polymer crystallization depends sensitively on the temperature Tc at which it occurs, more precisely on the degree of undercooling A T=Tm-Tc below the melting temperature Tm. Since we have to estimate Tm, at least roughly, of our lamellar crystal model, we first study the melting process of a lamella during the temperature increase at a constant rate. 

Additional neutron scattering studies on different polymer systems could prove very important. Strobl [31,32,47,103] provides evidence that, for some polymers, lamellar crystallization is preceded by pre-ordering of the melt followed by formation of planar arrays of blocks. Investigating crystallization from the melt, Kaji and coworkers [25] find pre-ordering phenomena relating to orientational fluctuations of stiff polymer segments which, under appropriate conditions, determine phase separation prior to crystallization. 

It is now possible to obtain the average lamellar thickness L. Assuming that the folds are incorporated into the lamellar crystal after a proper conformational straightening, and attributing a 0.127 nm axial advancement to each... 

Such a model for lamellar crystallization is now investigated. Initially the calculations are restricted to the simple lamellar model shown in Figure 1, but multiple fold lamellae are briefly considered even though they present a serious problem stemming from insufficient information about the number of folds. 

---