C&CB Seminar - Gabrielle Foran, McMaster University

Description

Solid-State NMR Analyses of Molecular Structure and Dynamics in Hydrogen-Bonded Materials

DATE: Thursday June 13, 2019
TIME: 1:30 pm with coffee cookies
LOCATION: ABB 165
SUPERVISOR: Dr. Gillian Goward


Solid-state NMR is particularly well-suited to the study of the structure and dynamics of hydrogen-bonded systems. In the work presented here proton dynamics were investigated in phosphate solid acids, a class of phosphate-based proton conductors, which have the potential to be used as solid state proton conductors in hydrogen fuel cells. Proton dynamics in phosphate solid acids were investigated using symmetry-based dipolar recoupling techniques. Site-specific proton dynamics in these materials were probed by monitoring the attenuation of the homonuclear dipolar coupling constant as a function of temperature. These studies showed that homonuclear dipolar recoupling NMR techniques can be employed in complex multi-spin systems. Additionally, two pathways for proton hopping in monoclinic RbH2PO4, a sample with multiple proton environments, were identified and quantified for the first time using a combination of dipolar recoupling and exchange NMR methods. In addition to providing a means for proton transport, hydrogen-bonded networks are also important structural components of many materials. To this end, hydrogen bonding was investigated as a coordination mode in silicone boronate acid (SiBA) elastomers, potential materials for contact lens manufacture. As in the phosphate-based proton conductors, hydrogen bonding played an important role in the structure of the SiBA elastomers as one of the mechanisms through which these materials crosslink. In addition to hydrogen bonding, covalent bonding between boronic acids was found to occur at three- and four-coordinate boron centers. The purpose of this study was to determine the influence of boronic acid loading and packing density on crosslinking in SiBA elastomers. Boron coordination environments were investigated by 11B quadrupolar lineshape analyses. The incidence of four-coordinate dative bonding, a predictor of the stress-strain response in these materials, increased with boronic acid loading but was most strongly influenced by boronic acid packing density.
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McMaster University - Faculty of Science | Chemistry & Chemical Biology