Probe diffusion in an aqueous polyelectrolyte solution

Using the technique of fluorescence photobleaching recovery, we have measured the tracer diffusion coefficients of probe particles in aqueous solutions of polystyrene sulfonate at various ionic strengths. Data were fit well by the expression D/D0=exp[−acν′], where D is the probe diffusion coefficient at polymer concentration c, D0 is the probe diffusion coefficient in the absence of polymer, and a and ν′ are familiar scaling parameters. The parameter ν′ ranged from a maximum of 1.0 for the conditions with maximum intersegment interaction (low salt, high-molecular weight, high-charge density) to a minimum of about 0.5 for the high-salt, low-charge density cases. The parameter a showed little sensitivity to polymer charge density or ionic strength but was a strong function of probe size. No discontinuities in the probe diffusion coefficients or analytical parameters were observed under any solution conditions, even though experimental variations included conditions that are expected to correspond to the transition to the semidilute concentration regime and to the ordinary–extraordinary phase transition.