An isolated, microscopic-sized polymer crystal with no intercrystalline molecular connections. Formed only by very slow crystallization from dilute solution (at < 0.1% concentration). Typically it consists of a lozenge-shaped lamella about 100¡Ê thick often resulting from a collapsed pyramidal crystal. The polymer molecules (typically about 10000¡Ê in length) have been shown by electron diffraction to tie oriented across the thickness of the crystal and hence must be chain folded. Melt crystallized polymer crystallites are also thought to have chain folded molecules. The interfold distance (and hence crystal thickness) depends on crystallization temperature and may be increased by annealing.

  The flat plate-like crystal or crystallite which is the characteristic crystal habit of most crystalline polymers and polymer single crystals. Typically it is of about 5-50 nm in thickness. Since the polymer chains have been shown by electron diffraction to lie across the thickness of  the crystallite, they must be folded at the chain surface (chain folding) owing to their length of several hundred nm.

  The smallest dimensional size of a lamellar polymer crystal or crystallite. It is highly dependent on crystallization conditions, especially the temperature, In folded chain srystals it has the same dimension as the polymer molecular length between folds. Generally it is in the range 5-50 nm. It may be determined by electron micrograph shadow length, samall angle X-ray scattering or interference microscopy. It can be increased by annealing (lamellar thickening).

  A branched multilayer lamellar crystal of tree-like morphology in which the overall shape of the single crystal is often retained. The branches diverge at wide angles to each other and are crystallographically related. Branching is more extensive with lower crystallization temperatures. Formed by crystallization from dilute solution at lower temperatures than used to grow single crystals.

  A spherulite whose growth is initiated by formation of a dendrite as a nucleus and whose large-scale branching, tree-like structure is still observable in the completely formed spherulite.

  A polyhedral multilayer lamellar crystal usually about 1 nm thick and about 10 ¥ìm in diameter. It is formed by crystallization from the melt or concentrated solution. The lamellae are connected with each other by tie molecules or by fibrous tie crystals. Thus a hedrite is intermediate in complexity between a single crystal and a spherute.

  An aggregation of crystallites as a spherical cluster, consisting of fibrillar crystalline lamellae (the fibril) radiating from the centre of the spherulite, or arising as branches. Amorphous polymer is present between the fibrils. Spherulites are the most noticeable morphological feature of most crystalline polymers, varying in size from about 0.1 ¥ìm to several millimeters, usually being in the range 1 ¥ìm to 0.1mm.

  The oriented growth of one crystalline substance on the surface of a crystalline substrate. In polymer crystallization this frequently involves growth of a folded chain polymer on an extended chain crystal of the same polymer, e.g. in the formation of shish-kebabs. In a wider sense all polymer crystallizations (apart from single crystal formation) are epitaxial since they are multi-crystalline with one crystallite influencing the orientation of its neighbour.