Amorphous polymers, orientation profile

Tadmor [136] used this description to interpret the orientation profile in amorphous polymers (see Fig. 15.33) the orientation in the skin is due to the fountain flow and the secondary maximum to the shear flow behind the front, with, in both cases, some relaxation of the orientation during cooling. This can be generalized to semicrystalline polymers, where the same type of orientation profile is found for the crystalline phase (e.g. [137]), even if it is sometimes difficult to find an orientation maximum at the surface, perhaps for experimental reasons. Additional effects may be introduced by the packing stage. The packing flow may induce a new secondary maximum in the orientation profile, but lower than the first one [137]. 

In SGC mats precipitated from dilute solutions (Fig. 8.4a), the lamellae are stacked and oriented parallel to the mat surface. The thicknesses for the amorphous and crystalline layers determined by TEM are 9nm for the crystalline layer and 1.5 nm for the amorphous one independent of the solution concentration. The sum of the thicknesses of the crystalline and amorphous phases coincides with the long periods of SAXS profiles [43]. Although the morphologies seem to be independent of polymer concentration, the peak intensity of SAXS indicates that an increase in electton density in amorphous layers with decreasing prior polymer concentration [44]. 

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