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Chain scission in turbulent flow of dilute polymer solutions
Flows with strong extensional components are capable of unraveling and breaking dissolved polymer chains, yielding a distribution of chain fragments that continually alters the molecular weight distribution, MWD, of a given sample over time of exposure to the flow. The evolution of the MWD is described in terms of scission rates and probabilities along the polymer backbone that a scission event will occur. These scission event probability distributions, p(f), where f is the fractional position along the backbone, depend on the flow condition, and quantitative characterization of the breadth of p(f) by the standard deviation relative to chain length, R, reveals information about the configuration of the chain at the time of scission. In this thesis, we have developed a generalized scission kinetics formulation that does not make unsupported assumptions regarding p( f), and applied this formulation to the analysis of MWDs, measured by quantitative gel electrophoresis, and arising from degradation of NaPSS in both turbulent Taylor-Couette and sonication flows. For the first time, we have reported R for turbulent flow-induced degradation and found that essentially random scission best describes the degradation process, with R = 9.5 for a single Gaussian description. Including the possibility of scission of a folded chain as a dual Gaussian description we found similarly that Rsingle = 9.5 and Rfolded = 0.09, with 70% of the chains breaking via the folded pathway, but with negligible improvement in the error in fit. We contrasted this result with our result for scission in sonication flow. With the single Gaussian description, we found a best fit R = 0.28, and with the dual Gaussian description, we found best fit parameters of Rsingle = 0.17 and R folded = 0.09, with the folded chain breaking more than twice as frequently. The latter fit was reduced 30% in error from the single Gaussian fit. In developing our understanding of the technique of quantitative gel electrophoresis, we have developed fundamental models of the diffusion-mediated, post-electrophoresic staining process. The single and dual binding models accurately predict the edge-like appearance of the diffusing dye front which is not predicted by the Crank model37 of probe diffusion in a binding medium.
Price, Brian Gray, "Chain scission in turbulent flow of dilute polymer solutions" (2002). Doctoral Dissertations Available from Proquest. AAI3056271.