Electron microscopy liquid crystal systems

Analogues of liquid crystals are numerous in biological systems (3 6,8-11). Certain fibrous and regularly twisted materials can be considered as polymerized cholesterics. Such twisted fibrous structures are recognizable by electron microscopy and sometimes by light microscopy, by the observation in thin sections of sets of stacked rows of nested arcs (fig. 1). The structure of a cholesteric system is represented in fig. 2 and the origin of the arced patterns is indicated in fig. 3. The first sketch (fig. 2) shows a section which is parallel to the twist axis. 

Liquid crystals do not lend themselves to electron microscopy, as a liquid phase cannot be easily handled within a vacuum column unless cumbersome wet stages are employed. However, the fact that polymeric liquid crystals can be quenched to the glassy or partially crystalline states without any apparent disturbance of the local orientation characteristic of the liquid mesophase means that the electron microscope becomes a most useful tool. It is now providing new insights into the local molecular orientation in some liquid crystal polymer systems. 

The morphologies of both ABA and ANA homopolymers and 73/27 ABA/ANA copol5nner prepared by thin-film polymerization show that crystallization occurs in the homopolymerization systems and the liquid crystal state remains stable in the copolymerization system (39-44), clearly indicating that the random copolymerization is an effective way to retard the crystallization. Transmission electron microscopy revealed that the microstructures of homopol5nners of ABA and ANA had more obvious lamellar texture (41-44). 

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