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Supramolecular and solid state dynamics of selected Dianin's clathrates
Abstract
This dissertation investigates the supramolecular and solid state dynamics of the clathrand (empty host) and the ethanol and heptanol clathrates of 4-p-hydroxyphenyl-2,2,4-trimethyl chroman (Dianin's compound). Elastic constants measured through Brillouin scattering illustrate that the size, type, number, and orientation of the guest molecule(s) in the Dianin's cages play a dramatic role in delineating these systems' phonon dynamics. The c$\sb{33}$ elastic constants indicate the introduction of progressively larger guest molecules substantially weakens the lattice along the three-fold cage axis. Comparison with the empty clathrand indicates a decrease in stiffness of 20% and 25% for the ethanol and heptanol clathrates, respectively. The c$\sb{44}$ elastic constant, which measures the resistance to yz shear, exhibits an identical trend with the clathrand being the stiffest followed in order by the ethanol and heptanol clathrates. The most surprising aspect of the measured elastic constants was that both the c$\sb{11}$ and c$\sb{12}$ elastic constants for the ethanol clathrate were larger than those for the clathrand. This result implies that the ethanol guest molecules provide stability to the host lattice in the hydrogen-bonded hexamer plane. The measured elastic constants for the heptanol clathrate indicate that the introduction of heptanol guest molecules dramatically weakens the overall structure of the lattice. The Brillouin scattering experiments show that the longitudinal acoustic modes propagating along the z (c)-axis are dramatically attenuated for increasing size of the guest. Comparison of the acoustic absorption coefficients between the ethanol clathrate and clathrand indicate a 47% increase in attenuation of the heat carrying acoustic modes. Acoustic attenuation along the z (c)-axis is amplified for the heptanol clathrate where an increase of 80% compared to the clathrand is observed. And finally, the first observation of global vibrations of the entire supramolecule are reported. The presence of an optic mode with a vibrational frequency ($\sim$.5 cm$\sp{-1})$ on the order of the heat carrying acoustic modes and of low frequency intramolecular vibrations (85 cm$\sp{-1}$-129 cm$\sp{-1})$ gives direct evidence that Raman modes are active in the resonant scattering of thermal phonons.
Subject Area
Chemistry|Condensation|Materials science
Recommended Citation
Sandstedt, Christian A, "Supramolecular and solid state dynamics of selected Dianin's clathrates" (1998). ETD collection for University of Nebraska-Lincoln. AAI9908484.
https://digitalcommons.unl.edu/dissertations/AAI9908484