Thermal, mechanical and electrical properties of liquid crystalline polymer electrolytes
It is generally accepted that ion transport in polymer electrolytes is strongly coupled to the local viscosity of the host polymer and that, in most cases, appreciable ionic conductivity below the glass transition temperature is not observed. Recent literature suggests that this may not always be the case and examples of polymer electrolytes exhibiting ionic conductivity decoupled from the polymeric motions have been reported. This thesis investigates one such system, a liquid crystalline polymer electrolyte, which has been reported to show measurable conductivity in the sold phase. The aim is to investigate such decoupled behaviour, how it may be optimised and to understand the conductivity mechanism. The thermal, mechanical and electrical properties of lithium perchlorate and lithium triflate complexes of a liquid crystalline polymer and its non-liquid crystalline analogue have been investigated. These studies suggest that the conductivity is not in fact decoupled from the local motions of the polymer. Selected complexes are then examined further and conductivities measured under variable pressure. From these data, activation energies, volumes and decoupling constants are calculated. These results show that, although not fully coupled, these complexes cannot be considered to exhibit decoupled conductivity and, in fact, the non-liquid crystalline electrolytes actually show a greater tendency towards decoupled behaviour than their liquid crystalline counterparts. In the final chapter, the two polymers are complexed with lithium trifluoromethanesulphonyl imide, a salt that has been reported to give enhanced conducivities. It is found that using this salt does indeed raise conductivities, but also reduces tendencies towards decoupled behaviour.