Master of Science (MS)
In 1978, Lee found an increase and then a large decrease in the diffusion coefficient of poly(lysine) as the concentration of salt is decreased (Lin, S. C.; Lee, W. I.; Schurr, J. M. Biopolymers 1978, 17, (4), 1041-1064). Since the “slow mode” discovery, many have studied it without finding a fully satisfactory answer. Additional dynamic light scattering (DLS) measurements have been the main experimental technique used for reinvestigating the slow mode decay. Although DLS is a powerful characterization tool, it depends on thermodynamic interactions. As complicated as they can be, thermodynamic interactions are much worse for polyelectrolytes because of the charges on the polymer. This creates a difficult predicament for slow mode decay study: the slow mode decay was first discovered using DLS but DLS is not the best way to study it. Another problem with polyelectrolytes is weak scattering. Other problems associated with a DLS experiment are the tedious cleaning needed to remove dust prior to measurements, and the long acquisition times needed for a weak scatter. Therefore, other techniques are needed for the study of the slow mode decay. Polystyrene sulfonate (NaPSS) is a commonly studied polyelectrolyte but it is not ideal. In efforts to keep the polydispersity low, NaPSS is synthesized by anionic polymerization with sulfonate groups added after synthesis of the polymer. This may allow hydrophobic patches along the polymer and could lead to aggregation in aqueous solutions, further convoluting the study of the slow mode decay. Herein, an essentially 100 % sulfonated fluorescent NaPSS is synthesized, allowing for study by fluorescence photobleaching recovery (FPR) without the possibility for “false” aggregation by the hydrophobic patches. FPR has advantages for studying the slow mode decay compared to DLS. In a FPR experiment, the thermodynamic interactions are so small they can be ignored. DLS depends on the thermodynamics of the solution; by using FPR, the slow mode problem can be made simpler (although it still is not easy). Also, the distance scale probed can be longer, thus ignoring internal motions and rotational dynamics. The amount of time needed to run a FPR experiment is much less than DLS and dust is advantageous rather than a nuisance.
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Huberty, Wayne Alfred, "Synthesis of fluorescent poly(styrene sulfonate)" (2012). LSU Master's Theses. 2587.