Anisotropic ionic conduction in a magnetically aligned liquid crystalline polymer electrolyte

Sequentially ordered thermotropic main-chain liquid crystalline polymers based on modifications of terephthaloyl-bis-4-oxybenzoyl copolymerised with polyethylene glycol (TOB-PEG) have been synthesized. Materials of interest typically have a T-g below ambient, a crystalline melt transition around 100 degrees C, and exhibit a number of complex liquid crystalline phases with clearing ranges to isotropic in the region 120-180 degrees C. The variation of ionic conductivity with temperature of complexes formed with LiCF3SO3 is typically in the range 10(-9) S/cm at ambient to 10(-5) S/cm at 130 degrees C, and reveals discontinuities of slope which correlate with changes of phase in the material. Selected unsalted materials have been aligned magnetically using a 7.1T superconducting magnet and show ordering at ambient temperatures characteristic of a smectic C type configuration. Polymer electrolytes formed with LiCF3 SO3 (EO/Li in the range 30 to 75) have also been magnetically aligned and bulk ionic conductivities measured parallel (sigma(parallel to)) and perpendicular (sigma(perpendicular to)) to the alignment direction measured, aii is significantly reduced over the isotropic polymer by a factor of more than;five due to the blocking smectic-type layers. When heated to the onset of the melt, sigma(perpendicular to) shows an unexpected increase attributed to the opening up of aligned conduction channels of PEG. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.