Doctor of Philosophy (PhD)
This dissertation is concerned with random coil and rodlike polymer diffusion in complex solutions. The development of fluorescence photobleaching recovery, FPR, as a technique to determine polymer molecular weight distributions by measuring the diffusion distribution and converting it to a molecular weight distribution using a calibration curve is first covered. Fluorescently tagged probes were individually dissolved in polymer solutions at negligible amounts and measured with FPR to construct the calibration curve of self-diffusion vs. molecular weight. Once calibration curves were constructed, bimodal distributions were separated using the matrices corresponding to the calibration curves. The diffusion of the probes and separation results are explained in terms of the matrix solution properties. Separation of a dextran bimodal distribution was unsuccessful, a pullulan bimodal separation succeeded, and the simulations indicate the method is feasible to measure molecular weight distributions. With more studies, detecting polymer molecular weight distributions with FPR can become a quick screening method as shown by this preliminary study. The second study looks at the dynamics of a rodlike polymer in solution as it crosses from an isotropic to liquid crystal phase. Three different lengths of poly(γ-benzyl-α, L-glutamate) were fluorescently labeled and dissolved in unlabeled PBLG solutions spanning concentrations from a semidilute isotropic to concentrated liquid crystal solution. The diffusion of the solutions was measured using FPR. PBLG with molecular weights of 134500 and 232000 g mol-1 show an increase in diffusion as the lyotropic regime is entered while 24600 g mol-1 sample does not. Factors affecting the discrepancy of PBLG-24600 might be a different lyotropic morphology or an absence of a transition zone from isotropic to liquid crystal phase.
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Doucet, Garrett John, "Dynamics of complex polymer solutions: putting diffusion to work and exploring rigid rod diffusion" (2004). LSU Doctoral Dissertations. 3842.
Paul S. Russo