Diffusion of Labeled Polyelectrolytes in an Unlabeled Polyelectrolyte Matrix Solution

Fluorescence photobleaching recovery (FPR) was used to investigate the diffusion of fluoresceinamine-labeled poly(styrene sulfonate sodium salt) (LNaPSS, various molecular weights) in a matrix of unlabeled poly(styrene sulfonate sodium salt) (NaPSS, $M_{w}$ = 990,000). FPR selectively monitors the optical tracer self-diffusion coefficient of LNaPSS ($D)$. No long-term aggregates were detected. The matrix polymer slowed the self-diffusion of LNaPSS. When measuring $D$ of LNaPSS with three different molecular weights over the same range of matrix concentration, the results depended on molecular weight of the LNaPSS. When the matrix concentration exceeded 20 mg/g of water, $D$ was almost inversely proportional to molecular weight. In-situ dialysis FPR studies show that with the addition of salt, $D$ decreases more dramatically with matrix than without matrix.