A new determination of molecular mobility in amorphous materials:

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 that the effect is not that of larger group but rather that of group (like methoxy and ethoxy) not able to hydrogen bond to matrix, which can have a coupling the probe vibrations to the matrix. Vanillin phosphorescence demonstrated that the average rate of matrix molecular mobility rates increases with an increase in the molecular size and Tg of the sugar in the glucose homologous series. A comparative study of mobility in three excipients sucrose, trehalose and PVP, using vanillin phosphorescence provided useful insight about their stabilizing effect. The phosphorescence from probes erythrosin B, vanillin and tryptophan was successfully utilized to measure molecular mobility on three different time scales corresponding to each probe in amorphous sucrose and protein film. Molecular mobility was successfully studied in amorphous sucrose films by monitoring phosphorescence from the dual probe combination of erythrosin B: vanillin, erythrosin B: tryptophan and vanillin:tryptophan.Ph.D.Includes bibliographical referencesby Rashmi Satyanarayan Tiwar