A chapter on liquid crystals is relevant to a book on fibrous composites for three main reasons: They both are mobile, they have similar architectures, and they both can self-assemble. The fibres of natural composites consist of large water-insoluble molecules which are put into place extracellularly. To be effective, these macromolecules must be strategically oriented (see Chapter 3). During development they therefore require to pass through a mobile phase, during which their positions can be adjusted, before solidification takes place. This chapter will show how liquid crystals meet this requirement.

The similarities between liquid crystals and insect cuticles were realized independently by Conmar Robinson (a retired polypeptide chemist) and myself and were presented in talks to a symposium on insect cuticle held in the Shell Building (London) in 1967. One presentation emphasized the optical similarities in the two systems (Robinson, 1966); the other compared their helicoidal structures and proposed that insect cuticular ultrastructure might develop by self-assembly via a liquid crystalline stage (Neville & Luke, 1969b). One of my main contributions has been subsequently to develop this idea in other systems, including plant cell walls, moth eggshells, fish eggshells, and mantis eggcases. The hope is that this will encourage biochemists to recognize features of structural chemistry which are relevant to liquid crystalline self-assembly.

A significant difference exists between biological composites and liquid crystals, despite their similar architectures. The fibrous component in composites consists of crystallites (small parallel bundles of molecules), whereas that of liquid crystals consists of individual molecular chains. The full significance of this difference is not yet understood (see, however, Section 4.3c).