Fluorescence studies of polymer association in water and droplet coalescence in polymer blend melts

grantor: University of TorontoThe first part of this thesis is a study of aqueous solutions of two associative polymers by pyrene fluorescent probe experiments. The polymers we studied are based on a linear monodisperse poly(ethylene oxide) of Mn = 35,000, with C16H33 and C18H37 end groups. The hydrophobic end groups of this polymer associate forming micelle-like structures, which serve as solubilization sites for the pyrene molecules. Fluorescence decay profiles of pyrene were fitted to the Poisson quenching model to obtain the fitting parameter n, the mean number of quenchers per micelle. From the values of n we calculated the end-group aggregation number NR over a range of polymer concentrations, from 0.1 to 17 wt.%. We found that the aggregation number increases with the polymer concentration. The second part of the thesis examines various aspects of latex blend films. The main component (90 wt.%) in the blend is a soft polymer PEHMA [poly(2-ethylhexyl methacrylate)]. The minor component (10 wt.%) is a harder polymer PBMA [poly(butyl methacrylate)], dispersed as 120 nm spheres in the PEHMA matrix. The PBMA particles were labeled with 1 mol.% of covalently bound fluorescent dyes, either phenanthrene or anthracene. We studied shear-induced coalescence in these blends, both 'in line', using a home-built Rheo-Fluo device consisting of a parallel plate rheometer and a fiber-optic assisted fluorescence detection system, and 'off line', using laser scanning confocal fluorescence microscopy. We evaluated the mean size and the width of the particle size distribution of the dispersed phase at various shear rates and found that the size first increases (after 1 hour of shearing) and then decreases (after 10 hours). Comparison with the results obtained under quiescent conditions indicated that shear is highly efficient in promoting coalescence. We also studied the effects of the film preparation conditions on the morphology of the newly formed films and found that in the presence of the surfactant SDS (2 wt.%) the PBMA particles flocculate forming network-like structures. When the surfactant is removed from the dispersion by ion exchange, the blend morphology is uniform. Finally, we evaluated the interface thickness 8 between PBMA and PEHMA using the nonradiative energy transfer method.Ph.D