Effect of Valence and Chemical Species of Added Electrolyte on Polyelectrolyte Conformations and Interactions

The effect of added electrolyte (AE) valence and species on polyelectrolytes was studied using automatic, continuous mixing (ACM), allowing measurements over composition gradients. The second virial coefficient A 2 was decomposed into contributions from an electrostatically sensitive mean-square gyration radius 〈 S 2 〉 and an external electrostatic field. 〈 S 2 〉 matched predictions of combined electrostatic persistence length and excluded-volume theories, without adjustable parameters. A 2 was modeled via an equivalent, soft-core, expansible, charged sphere. Whereas the scaling behavior of 〈 S 2 〉, intrinsic viscosity [η], and A 2 was the same for all AE, the prefactors strongly depended on AE symmetry and valence. At given ionic strength 〈 S 2 〉, [η], A 2, effective linear charge density, and expansible sphere surface potential are less for divalent than monovalent AE. Different ion species for a given valence class showed second-order effects following a Hoffmeister series. ACM should also prove valuable for investigating AE-induced phase transitions in polyelectrolytes like DNA and proteins.