Date of Award
Doctor of Philosophy (PhD)
Cornelius , Christopher J.
Stuart , Steven J.
McNeill , Jason
The structure and transport characteristics in a novel family of ionomers consisting of a hydrophobic polyphenylene backbone substituted by sulfonic acid functionalized phenyl side chains (sPPs) have been investigated. These polymers have potential applications in electrochemistry as well as separation both as membranes and thin films. The bulk structure as a function of hydration has been explored by X-ray and neutron scattering. Interfacial structure was studied by AFM and neutron reflectometry. The characteristics of water in the bulk were studied by NMR and FTIR and that in thin films by neutron reflectometry.
The sPPs exhibit characteristic structure due to their rigid backbone and high glass transition temperature of the unsulfonated polyphenylene. The ionomers associate into bundles in dilute solutions. This structure persists from solution to dry thin films and membranes. This bundled structure is only slightly sensitive to changes in temperature and they are affected by the degree of sulfonation. With hydration, structural changes take place. At the initial stage, water penetrates into interstitial spaces between the bundles of polymers, followed by rearrangements of domains to yield a locally bicontinuous ionomer of sulfonated and unsulfonated domains.
When cast into thin films, interfacial interactions affects the structure of the ionomers, penetration processes of solvents as well as solvent distribution within the films. Penetration of water and methanol are studied revealing that the process is dependent on the film thickness and ionic strength of the polymer. The initial stage of solvent diffusion follows Fickian characteristics. The distribution of the solvents within the films is not uniform.
The complex environments experienced by water molecules confined in the ionomers include hydrophilic and the hydrophobic regimes. The water behavior strongly depends on the degree of sulfonation of the polymers, temperature and water content.
He, Lilin, "STRUCTURE AND TRANSPORT CHARACTERISTICS OF HIGHLY RIGID IONOMERS" (2008). All Dissertations. 246.