Date of Award
1991
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
Photophysical and photochemical examinations of polycyclic aromatic hydrocarbons adsorbed on metal oxide surfaces provide indirect evidence for the mobility of these species. We employ Fluorescence Photobleaching Recovery (FPR) to directly measure the mobility of naphthacene on various silica gel surfaces at low coverages. On normal phase silica, the rate of diffusion is found to be invariant of the surface treatment. The diffusion coefficient is constant at 2.5 {dollar}\times{dollar} 10{dollar}\sp{lcub}-10{rcub}{dollar} cm{dollar}\sp2{dollar} s{dollar}\sp{lcub}-1{rcub}{dollar}, but the mobile fraction shows a pronounced dependence on surface treatment. These results indicate that the mobility of the same population of naphthacene is being measured in each case, but the fraction of molecules in that population changes with surface preparation.;The mobility of naphthacene is significantly greater on silica gels derivatized with long chain hydrocarbons. Both the diffusion coefficient and the mobile fraction are greatly increased. The largest values for both the diffusion coefficient and mobile fractions are found for naphthacene on silica first derivatized with C18 chains then further derivatized by coadsorption of undecanol, or normal phase silica with physisorbed myristic acid. Increased diffusion on derivatized surfaces is interpreted as the probe interaction with the coating more than the silica surface. Chemical derivatization yields heterogeneous incomplete coatings, whereas physical derivatization leads to more complete homogeneous coatings.;Photophysical investigations of naphthacene both in solution and on silica are carried out in order to examine the possibility of a link between previous photophysical studies and direct diffusion measurements. It appears that a direct link cannot be made.;Photochemical studies of naphthacene in solution and on silica are performed from a kinetics perspective. Naphthacene photolyzes to two types of products, depending on conditions. In solution, both pathways are first order in naphthacene. On silica, the kinetics are not as simple. This leads to further development of FPR theory which previously assumed first order bleaching only. If the bleaching process is second order, little effect on the mobile fraction is seen, but the diffusion coefficient will be underestimated using the current FPR theory.
Recommended Citation
Bjarneson, David Wayne, "Investigation Of Naphthacene Mobility On Silica" (1991). Digitized Theses. 1939.
https://ir.lib.uwo.ca/digitizedtheses/1939