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Polymer Spherulites: A Modern Assessment

Spherulites and spherulitic growth are characteristic of melt-crystallized polymers and exert a profound influence on their mechanical and other properties. They and their formation have, nevertheless, for long remained poorly understood principally because of inadequate knowledge of their lamellar microstructure so that the problem that needed to be explained was not well defined. Since the subject was last surveyed, the situation has changed substantially: the proposals of pertinent growth mechanisms then current have now been tested and confirmed in considerable detail. At the same time, novel phenomena have brought new insights into the molecular mechanisms of self-organization of long molecules. It is fair to say that we do now have the basis of a fundamental understanding of spherulitic growth, at least in polymers, but that also appears capable of extension to other systems. Spherulites are encountered widely in nature, commonly forming from viscous and impure melts, but are best characterized in crystalline polymers not least because of the detailed record of growth preserved in the lamellar microstructure; in systems with small molecules, sample history is not so readily retained nor identified. A spherulite is literally a little sphere, which is the shape of an isolated mature object, but the use of the term also needs to accommodate the variety of earlier forms actually observed; the concomitant spatial ordering normally extends over at least microns, encompassing many crystals. The polarizing optical microscope is generally the most convenient means of observation, requiring specimens in the form of a thin film, say 10mm thick, which may