Lamellae liquid crystalline, chain folding

Semicrystalline polymers contain liquid-like amorphous and ordered crystalline phases. When solidified from the pure melt, these polymers show a spherulitic structure in which crystalline lamellae composed of folded chain crystallites radiate from the center of the spherulite in such a way that a constant long period or crystallinity is apvproximately maintained. The amorphous regions reside in the interlamellar regions in the form of tie chains, whose ends are attached to adjacent lamellae loop chains, whose ends are attached to the same lamella cilia chains with only one end attached to a lamella (or dangling chain ends), and floating chains which are not attached to any lamellae. This hierarchical structure is illustrated in Figure 1. 

The most direct evidence of the crystallinity in polymers is provided by x-ray diffraction studies. The x-ray patterns of many crystalline polymers show both sharp features associated with regions of three-dimensional order, and more diffuse features characteristic of molecularly disordered substances like liquids. The occurrence of both types of feature is evidence that ordered regions (called crystallites) and disordered regions coexist in most crystalline polymers. X-ray scattering and electron microscopy have shown that the crystallites are made up of lamellae which are built-up of folded polymer chains as explained below. 

Where v and /j. are the number of stems in the length and breadth of the lamella, ao and bo are the cross-sectional dimensions of a stem, I is the thickness of the lamella, AG is the difference in bulk free energy between the crystalline and liquid phases, ag is the fold surface free energy, and a is the side surface free energy. This then leads to the rate of formation I of folded chain nuclei given by... 

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