dc.contributor.advisor | Van Horn, J. David | |
dc.contributor.author | Wu, Fei | |
dc.date.issued | 2017 | |
dc.date.submitted | 2017 Fall | |
dc.description | Title from PDF of title page viewed May 21, 2018 | |
dc.description | Dissertation advisor: J. David Van Horn | |
dc.description | Vita | |
dc.description | Includes bibliographical references (pages 171-172) | |
dc.description | Thesis (Ph.D.)--Department of Chemistry and Department of Physics and Astronomy. University of Missouri--Kansas City, 2017 | |
dc.description.abstract | Positron annihilation in various materials has been applied to characterize
microstructure for decades. In this work, PALS was used to study material nanostructure,
with a focus on the size and density of free volume and hole relaxation properties in
polycarbonate (PC) and polymethylmethacrylate (PMMA); fundamental studies of
polarized positron interaction with chiral crystals were also studied.
Free volume relaxation in PC and PMMA with different levels of simple shear
orientation was studied by PALS. Effects of applied pressure on the free volume recovery
were evaluated. Combining the bulk- and pressure-dependent PALS analyses, the
removal of applied pressure led to free-volume relaxation in all samples studied. The
alignment of the polymer chains and free-volume holes imposes molecular restrictions on
the molecular mobility of both PC and PMMA in their glassy states. Results indicated
that the relaxation of the free volume holes at temperatures below glass transition is
mostly reversible.
Longitudinally polarized positron particles were used to reveal asymmetric
interactions in chiral quartz crystals. Experimental results showed a significant intensity
difference in free positronium annihilation for left handed (LH) and right handed (RH)
chiral quartz crystals. Doppler broadening energy spectra (DBES) of z-cut LH or RH
quartz disks at different angles were also measured by an “S parameter” to probe the
observed difference. It was found that obtained annihilation energy difference of DBES
was in agreement with the result of positron annihilation in bulk chiral crystals.
PALS was used to compare different orientations and confirm asymmetric
interactions in natural versus synthetic quartz LH and RH crystals in z and non-z
orientations. Significant lifetime and intensity differences in free positronium annihilation
for LH and RH quartz crystals were observed. The trend was found to be same in the
related crystallographic orientations of the LH or RH crystals; the direction of incident
positrons, z or non-z, did not affect the observed differences in lifetime and intensity
trends. The results confirmed the existence of differential interactions of positronium
with the asymmetric lattice structures of LH and RH quartz crystals. | eng |
dc.description.tableofcontents | Introduction -- Experimental -- Study of amorphous polymers using PALS -- Positron interactions with chiral quartz -- Positron interactions with chiral quartz in non-z direction | |
dc.format.extent | xvii, 173 pages | |
dc.identifier.uri | https://hdl.handle.net/10355/63276 | |
dc.publisher | University of Missouri--Kansas City | eng |
dc.subject.lcsh | Positron annihilation | |
dc.subject.lcsh | Polycarbonates | |
dc.subject.lcsh | Polymethylmethacrylate | |
dc.subject.lcsh | Chirality | |
dc.subject.lcsh | Quartz crystals | |
dc.subject.other | Dissertation -- University of Missouri--Kansas City -- Chemistry | |
dc.subject.other | Dissertation -- University of Missouri--Kansas City -- Physics | |
dc.title | Positron interactions with oriented polymers and with chiral quartz crystals | eng |
dc.type | Thesis | eng |
thesis.degree.discipline | Chemistry (UMKC) | |
thesis.degree.discipline | Physics (UMKC) | |
thesis.degree.grantor | University of Missouri--Kansas City | |
thesis.degree.level | Doctoral | |
thesis.degree.name | Ph.D. | |