Crystals, single spherulites

Figure 7.2 Morphological phase boundary for the sPP/POE blends at several isothermal crystallization temperatures and compositions (S, A, and P correspond to single crystal, single-crystal aggregate, and spherulite of sPP, respectively).

Li L-S (1986) On the morphology and structure of poly(p-phenylene terephthalamide) single crystals and spherulites. J. Macromol. Sci.-Phys., B25 215... 

Figure 1.6 In situ optical microscope images of a single spherulite (set A) and the corresponding 3D images of intensity distribution of different conformational bands. Sets B and C refer to 1303 and 998 cm" bands, respectively. 1-3 are collected at different times during isothermal crystallization at 142 °C. The scale bar is 50 pm. Cong et al. [22]. Reproduced with permission of American Chemical Society.

Figure 5.1 (a) The solution-grown polyoxymethylene single crystal, (b) spherulites of melt-cooled polyethylene sample and the hierarchical structure, (c) extended-chain crystals of polyoxymethylene (whisker), and (d) the shish-kebab structure. (See color insert.)... 

The volume inside the semicrystalline polymers can be divided between the crystallized and amorphous parts of the polymer. The crystalline part usually forms a complicated network in the matrix of the amorphous polymer. A visualization of a single-polymer crystallite done [111] by the Atomic Force Microscopy (AFM) is shown in Fig. 9. The most common morphology observable in the semicrystalline polymer is that of a spherulitic microstructure [112], where the crystalline lamellae grows more or less radially from the central nucleus in all directions. The different crystal lamellae can nucleate separately... 

Johannsenite, Ca(Mn,Fe )Si206, is a species in whieh p = 0. There is little additional trivalent ion (Al, Fe, or Cr ) substitution. The mineral is most commonly found as spherulitic aggregates of brittle fibers or prisms. Another pyroxene, acmite (NaFe Si206), has been found as large (100 X 35 X 20 cm) single crystals of prismatic shape, as needles, as felted aggregates of fine fibers, and as capillary crystals. 

Study of the Crystalline Regions. According to our morphological studies, the crystalline structure of UHMWPE pseudo-gel was different under different sample preparations. For example, spherulites and lamellar single crystal stacks were observed when the pseudo-gel was prepared under quiescent conditions, shish-kebab crystals under stirring conditions, and a mixture of single and shish-kebab crystals under uncontrolled conditions (10). 

Many polymers form more complex single crystals when crystalhzed from dilute solution including hollow pyramids that often collapse on drying. As the polymer concentration increases, other structures occur, including twins, spirals, and multilayer dendritic structures with the main structure being spherulites. 

For linear PE, the initial structure formed is a single crystal with folded chain lamellae. These quickly lead to the formation of sheaflike structures called axialites or hedrites. As growth proceeds, the lamellae develop on either side of a central reference point. They continue to fan out, occupying increasing volume sections through the formation of additional lamellae at appropriate branch points. The result is the formation of spherulites as pictured in Figures 2.15 and 2.16. 

While the lamellar structures present in spherulites are similar to those present in polymer single crystals, the folding of chains in spherulites is less organized. Further, the structures that exist between these lamellar structures are generally occupied by amorphous structures including atactic chain segments, low molecular weight chains, and impurities. 

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