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dc.contributor.authorRoy, Abhisheken
dc.date.accessioned2014-03-14T20:07:59Zen
dc.date.available2014-03-14T20:07:59Zen
dc.date.issued2008-02-19en
dc.identifier.otheretd-03052008-002040en
dc.identifier.urihttp://hdl.handle.net/10919/26365en
dc.description.abstractThe major challenge of the research was to characterize and develop concepts for establishing structure/property relationships between the functionality of the polymer backbone, the states of water and the membrane transport properties. Most of the hydrocarbon based random copolymers reported in the literature show reduced proton conductivity at low water content. This was attributed to the formation of an isolated morphology. Over the last few years our group has synthesized thermally stable multiblock copolymers with varying chemical structures and compositions. Block copolymers consist of two or more incompatible polymers (i.e. blocks) that are chemically conjoined in the same chain. The transport properties of the multiblock copolymers showed a strong dependence on the morphology in contrast to the random copolymers. Irrespective of the nature of the backbone, the transport properties scaled with the block lengths of the copolymers. An increase in block length for a given series of block copolymer was associated with improved proton conduction, particularly under partially hydrated conditions compared to the random copolymers. The structure-property relationship of the proton conductivity and self-diffusion coefficient of water was obtained as a function of the volume fraction of water for all the random and block copolymers. At a given volume fraction, the block copolymers displayed both higher self-diffusion coefficients of water and proton conductivities relative to the random copolymers. This improvement in transport properties indicates the presence of desired and favorable morphology for the blocks. For DMFC applications, the block copolymers also showed low methanol permeability and high selectivity. The states of water in the copolymers were characterized using DSC and NMR relaxation techniques. At similar ionic contents, the free water concentration increased with increasing block lengths. The distribution of the states of water in the copolymers correlates to transport properties. This knowledge, coupled with the state of water experiments, transport measurements, and chemical structure of the copolymers provided a fundamental picture of how the chemical nature of a phase separated copolymer influences its transport properties. The experimental procedure involved impedance spectroscopy, DSC, TGA, FTIR, DMA, pulse gradient stimulated echo (PGSE) NMR, NMR relaxation experiments and various electrochemical fuel cell performance experiments.en
dc.publisherVirginia Techen
dc.relation.haspartAbhishekRoyETD.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectMorphologyen
dc.subjectTransporten
dc.subjectBlock Copolymeren
dc.subjectStates of Wateren
dc.subjectProton Exchange Membranesen
dc.titleStructure Property Relationships of Proton Exchange Membranesen
dc.typeDissertationen
dc.contributor.departmentMacromolecular Science and Engineeringen
dc.description.degreePh. D.en
thesis.degree.namePh. D.en
thesis.degree.leveldoctoralen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.disciplineMacromolecular Science and Engineeringen
dc.contributor.committeechairMcGrath, James E.en
dc.contributor.committeememberLesko, John Jacken
dc.contributor.committeememberDavis, Richey M.en
dc.contributor.committeememberBaird, Donald G.en
dc.contributor.committeememberRiffle, Judy S.en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-03052008-002040/en
dc.date.sdate2008-03-05en
dc.date.rdate2009-04-03en
dc.date.adate2008-04-03en


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