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Oldfield, Eric Chung, John 2011-05-07T13:43:11Z 2011-05-07T13:43:11Z 10000-01-01 1991 "We have studied a variety of macromolecular systems such as lipid/water lyotropic phases and elastomeric polymers, and in addition a thermotropic liquid-crystal displaying macroscopic orientational ordering behavior, by Carbon-13 ($\sp{13}$C) nuclear magnetic resonance (NMR) spectroscopy. We find that under ""magic angle"" spinning (MAS) these systems display high resolution due to extensive motions, and therefore traditional proton-decoupling is not necessary. In the absence of proton decoupling, i.e., proton-coupled MAS (PCMAS), we find that these systems display scalar hyperfine-coupled $\sp{13}$C splittings with radically asymmetric linewidths and shapes. We attribute these effects to cross-correlation terms between two or more different relaxation mechanisms, (dipolar/chemical shift anisotropy (DD/CSA) relaxations) at the high magnetic fields employed." Since the DD/CSA effects are quite novel and have not been treated in detail experimentally or theoretically, we have extended the previous theories to a more realistic anisotropic motional model and have attempted to explain the proton-coupled $\sp{13}$C longitudinal relaxation data in two elastomers by fitting it to the simple model. The data does not explain the model in an intuitively reasonable fashion; and it is concluded that more work needs to be done in order to study a system with more experimental measurables which would allow for fitting to a more elaborate theory of restricted motions. "We have also tried to extend the usefulness of PC-MAS relaxation cross-correlation study to a thermotropic liquid crystal; and in the process we have determined the effects which sample spinning in a magnetic field can have on an ordered phase such as the nematic phase of a liquid crystal. Our findings indicate that rapid spinning of the sample can lead to destruction of the macroscopic order-director alignment along the sample spinner axis. In order to avoid this difficulty ""off-axis"" spinning experiments are done to show that the stability of the order director can be maintained. With the added precaution we show that proton-coupled $\sp{13}$C relaxation study is feasible in the nematic phase; and from the measured relaxation time constants we obtain macroscopic cross-correlation spectral densities, although the interpretation of these spectral densities is dependent on the of knowledge of the accurate static tensor elements." Made available in DSpace on 2011-05-07T13:43:11Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9210769.pdf: 3993379 bytes, checksum: 8760939145d3218d6373cbbbb36427c9 (MD5) Previous issue date: 1991 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:58:19Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:27:25-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9210769 (UMI)AAI9210769 http://hdl.handle.net/2142/22541 eng Copyright 1991 Chung, John Chemistry, Physical Proton-coupled carbon-13 sample spinning NMR studies of macromolecules and ordered systems text Chemistry Chemistry University of Illinois at Urbana-Champaign Dissertation Ph.D.