Growth of Polymer Crystals from Solutions

3 Epitaxial Crystallization An epitaxial crystallization can occur when one polymer component crystallizes on the surface of the film of the uniaxially oriented other polymer component. The polymer chains grow into crystals with their chain axes parallel to the chain direction of the polymer substrate. We observe similar phenomena for nanocomposite material, in which 

To grow a single crystal, we cool a hot dilute solution of POM of 0.1 wt% concentration to a fixed temperature. We then place a drop of the cooled solution on a carbon mesh, and observe the growth of a single crystal by using 

TEM (Fig. 5.1a). The width can be several micrometers and the thickness only a few hundred angstroms. The electron diffraction pattern shows that only the hkO reflections are detected in the case of trigonal POM, which indicates that the chain stems stand up in the direction normal to the crystal surface. Stokes is the first to indicate the possibility of chain folding by measuring the electron diffraction patterns of unoriented trans-l,A-polyisoprene, he found that the chain axis is normal to the film plane [9]. Later, Fischer, Till, and Keller made direct observations of polymer single crystals with a chain-folded structure. The concept of chain folding originates from this experimental evidence [10]. 

---

Besides the structures already discussed, more complex morphologies may be obtained from the growth of polymer crystals from solutions. The structure that emerges from the crystallization of a polymer is a function of a complex interaction of factors that include the type of solvent, solution temperature, concentration, and polymer molecular weight. Some examples of these structures include spiral growth, dendrites, and hedrites. 

---