The nature of polymer motion at elevated concentration is a matter of current scientific interest. The diffusion of charged ("polyelectrolyte") polymers through solutions of other polymers occurs in several contexts, including intra-and intercellular protein transport and in methods for isolation of recombinant DNAs. The investigators will undertake a systematic experimental study of polyelectrolyte-polymer interdiffusion under different conditions. Light-scattering spectroscopy will be used to study diffusion of polystyrene sulfonate, both in simple solution and in the presence of a second ("matrix") polymer. The matrix polymer and solvent will scatter no light because they will be isorefractive. Experimental variables to be varied systematically include the concentrations and molecular weights of the two polymers, and solution's ionic strength. By measuring polarized as well as depolarized spectra, the probe's self-diffusion coefficient as well as its rotational diffusion coefficient will be obtained. These will be compared with predictions of the available models of polymer dynamics, thereby testing these models and clarifying understanding of how polymers move in solution.
