  Complexation between anionic and cationic polyelectrolytes results in
solid-like precipitates or liquid-like coacervate depending on the added salt
in the aqueous medium. However, the boundary between these polymer-rich phases
is quite broad and the associated changes in the polymer relaxation in the
complexes across the transition regime are poorly understood. In this work, the
relaxation dynamics of complexes across this transition is probed over a wide
timescale by measuring viscoelastic spectra and zero-shear viscosities at
varying temperatures and salt concentrations for two different salt types. We
find that the complexes exhibit time-temperature superposition (TTS) at all
salt concentrations, while the range of overlapped-frequencies for
time-temperature-salt superposition (TTSS) strongly depends on the salt
concentration (Cs) and gradually shifts to higher frequencies as Cs is
decreased. The sticky-Rouse model describes the relaxation behavior at all Cs.
However, collective relaxation of polyelectrolyte complexes gradually
approaches a rubbery regime and eventually exhibits a gel-like response as Cs
is decreased and limits the validity of TTSS.
