Relaxation behavior by time-salt and time-temperature superposition of polyelectrolyte complexes from coacervate to precipitate
Samim Ali, Vivek Prabhu
Complexation between anionic and cationic polyelectrolytes in aqueous solutions results in solid-like precipitates or liquid-like coacervate depending on the strength and relaxation properties of ion-pairs that formed between oppositely-charged sites. However, the boundary between these two distinct phases is quite broad and the associated changes in the relaxation behavior of complexes across the transition regime is poorly understood in literature. In this work, the relaxation dynamics of complexes across this transition zone 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) principle at all salt concentrations, while the range of overlapped-frequencies for time-temperature-salt-superposition (TTSS) strongly depends on salt concentration Cs and shifts to higher frequencies as Cs is decreased. Our further analysis using the sticky-Rouse model indicates that the relaxation mechanism of ion-pairs remains self- similar across the transition zone. However, the collective relaxation approaches rubber-type behavior at longer chain length and time scales as Cs is decreased, thereby limiting the validity of TTSS.
and Prabhu, V.
Relaxation behavior by time-salt and time-temperature superposition of polyelectrolyte complexes from coacervate to precipitate, Gels-, [online], https://doi.org/10.3390/gels4010011
(Accessed November 30, 2023)