Control of Dynamics in Polyelectrolyte Complexes by Temperature and Salt

The linear viscoelastic responses for a series of polyelectrolyte complexes, PECs, made from pairs of poly[3-(methacryloylamino)propyltrimethylammonium chloride], a polycation, and poly(sodium methacrylate), a polyanion, having various molecular weights were measured. Time-temperature superposition (TTS) for broad and narrow molecular weight distributions revealed entangled behavior at low salt concentration for the longer polyelectrolytes studied. All characteristic lifetimes were slowed by "sticky" dynamics of positive, Pol ⁺ and negative, Pol ^- , pairing. Time-temperature-salt doping superposition (TTSS) was achieved by considering the dual effects of increasing salt concentration on PECs: the partner lifetimes of Pol ⁺ and Pol ^- were inversely proportional to [NaCl], as was the population of Pol ⁺ Pol ^- pairs. Relaxation times for polymer partnering, entanglement, and reptation were measured directly on some systems. Whereas the intrinsic (in the absence of salt ions) lifetime for Pol ⁺ Pol ^- pairs was determined to be on the order of 1 × 10 ^-4 s, salt doping provided a faster, extrinsic, channel for relaxation at the monomer scale. The time-salt shift factor was decomposed into contributions from Pol ⁺ Pol ^- partner lifetimes, the number density of Pol ⁺ Pol ^- pairs, and the volume fraction of polymer.