Patterned fluorescence photobleaching recovery on multicomponent sodium polystyrene sulfonate solutions to investigate temporal aggregrate formation.

Patterned fluorescence photobleaching recovery was used to investigate multicomponent mixtures of sodium polystyrene sulfonate (NaPSS) to further understand translational diffusion and formation of temporal aggregates observed in dynamic light scattering (DLS) of charged macromolecules. Mixtures consisted of fluorescein isothiocyanate labeled NaPSS probe and an unlabeled NaPSS matrix in salt concentrations that exceeded C_p/C_s=5.7. In an effort to entrain single polymers into temporal aggregates, the matrix concentration was increased for several molecular weight probe polymers. If dilute probes enter matrix polymer aggregates then probe diffusion would be dictated by the aggregate, independent of probe molecular weight. But measured self-diffusion depended on probe molecular weight, evidence against probe aggregate inclusion. Further, probe diffusion depended on matrix molecular weight, at least above the entanglement concentration, suggesting that probes do not become entrained in the temporal aggregates, but respond to the presence of matrix polymer. Diffusion in unimodal NaPSS systems obeyed theoretical scaling laws of D~C^-0.5 but did not exhibit bi-exponential decay behavior as would be expected for diffusers in and outside temporary aggregates.