A new determination of molecular mobility in amorphous materials

Abstract

OF THE DISSERTATION A New Determination of Molecular Mobility in Amorphous Materials. By RASHMI SATYANARAYAN TIWARI Dissertation Director: Dr. Richard D. Ludescher This research investigated how the steady-state and time-resolved emission and intensity of phosphorescence from vanillin (4-hydroxy-3-methoxy benzaldehyde), a commonly used flavor compound, can be used to probe molecular mobility when dispersed within amorphous pure sucrose films. The luminescence properties and photophysical events of vanillin as a triplet state probe in amorphous sucrose films as a function of temperature was successfully characterized. The peak energy, bandwidth and lifetime data suggest that it is sensitive to molecular mobility and can be used monitor molecular mobility in amorphous sucrose films. Time-resolved phosphorescence intensity decays from vanillin were multiexponential both below and above the glass transition temperature, indicating that the pure (single component) amorphous matrix was dynamically heterogeneous on the molecular level. Vanillin analogs (hydroxy, dihydroxy and ethyl vanillin)) phosphorescence lifetime were found to be extremely sensitive to the local environment in the amorphous sucrose in the glassy state and at the glass-to-rubber transition into the melt, and provided useful insight about the mechanism of vanillin sensitivity to molecular mobility. Based on this the capability of movement of methoxyl group about the C-O bond is thought to be the contributor to sensitivity of vanillin to matrix molecular mobility. The other possibility is