Dielectric Relaxation in Macromolecular Liquid Crystals

Abstract

The synthesis of polymeric materials incorporating mesogenic (liquid-crystalline) units in the late 1970s, which was pioneered independently by Finkelmann, Ringsdorf and Wendorff in Mainz,1 and by Shibaev and Plate in Moscow,2 has been received with great interest by the polymer and liquid crystal communities around the world. Hybridization of two distinctively different classes of substances, i.e. liquid crystals and polymers, produced bulk properties of new materials that were a melange of properties of constituent substances. The applied scientists found them appealing for their multifunctional character, especially of copolymers, which enable ‘engineering’ of desired properties of a material conferred by different units. While backbone chains provide polymer characteristics like viscoelasticity and good film- or fiber-forming properties, mesogenic units enhance and facilitate imposition of the orientational order of the material by external fields (electric, magnetic, flow gradient or anchoring field at a substrate), conferring at the same time the anisotropy of many physical properties intrinsic to liquid crystals. Further modification of a material can be made by incorporating into a copolymer chain other functional groups with desired properties. The new materials also attracted the attention of scientists studying fundamental properties of polymers and liquid crystals, since they brought into view completely new problems associated with molecular interactions on the inter- and intramolecular level. It is well known that the most characteristic properties of polymeric materials like fibers, plastics and rubbers depend directly on molecular mobility in these polymers. Similarly, molecular dynamics in liquid crystals direct their applications in contemporary electronic devices. Not surprisingly, therefore, study of correlations between the molecular dynamics and bulk properties is advancing our knowledge and enhancing the technological exploitation of these materials.