SYSTEMATIC STUDY ON THE STRUCTURE-DYNAMICS RELATIONSHIP OF POLY(ETHYLENE OXIDE)-BASED SINGLE-ION CONDUCTORS
Open Access
- Author:
- Wang, Jing-Han Helen
- Graduate Program:
- Chemical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- May 04, 2011
- Committee Members:
- Ralph H Colby, Thesis Advisor/Co-Advisor
Ralph H Colby, Thesis Advisor/Co-Advisor - Keywords:
- PEO-based ionomers
segmental relaxation
electrode polarization
ionic conductivity - Abstract:
- To optimize the design of ion-containing polymers for advanced devices, the effects of different structural factors on the electrical properties of single-ion conductors (ionomers) needs to be investigated. There will be three main focuses in this study: (1) the effect of ion content, (2) the effect of side chain flexibility, and (3) free and attached ion solvation by ether oxygen atoms. By the design of ionomer systems and systematically varying the chemical structure, the structure-dynamic relationship is closely examined for all the PEO-based ionomers synthesized. The chemical structures were characterized by 1H NMR, and the thermal behavior of the ionomers was studied using differential scanning calorimetry (DSC). The electrical properties were investigated by dielectric relaxation spectroscopy (DRS). The results of DSC Tg suggests that with increasing ion content, ions aggregate to form ion-rich regions with PEO chains incorporated in them and increase Tg significantly, and this is more pronounced with shorter PEO side chains where the abrupt increase in Tg occurs at lower ion content. When shorter PEO side chains are used, the flexibility of the polymer is restricted by the stiff polymer backbone, and the ion-dissociating ability of PEO is weakened that leads to more ionic aggregates. As the ion content of an ionomer increases, the conducting ion concentration and static dielectric constant is expected to increase until a limit is reached where the ion-ion and ion-dipole interactions restrict ionic mobility, and conducting ion concentration drop significantly. Moreover, in the comparison of a polycation system to a polyanion system with the counterions being analogs of the ions attached on the polymer, ether oxygen atoms solvate the free cations better than the attached cations. Last but not least, the incorporation of electron-deficient groups as anion receptors boosts the conducting ion concentration and static dielectric constant of the polycation system.