Relaxation Behavior by Time-Salt and Time-Temperature Superpositions of Polyelectrolyte Complexes from Coacervate to Precipitate

Abstract

Abstract: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 (C s ) and gradually shifts to higher frequencies as C s is decreased. The sticky-Rouse model describes the relaxation behavior at all C s . However, collective relaxation of polyelectrolyte complexes gradually approaches a rubbery regime and eventually exhibits a gel-like response as C s is decreased and limits the validity of TTSS.

Recent progress in the science of complex coacervation

“…37,57 The horizontal shift factor τ c (γ →γτ c ) accounts for changes in the stress-relaxation behaviour of the material, which is attributed to the weakening of electrostatic interactions via charge screening (Figure 11c). 37,57 This is analogous to the traditional time-temperature superposition, which has also been reported for coacervates 53,59 and polyelectrolyte complexes, 200 except that salt concentration weakens interactions (and expedites dynamics) rather than temperature.…”

“…Surface properties such as the interfacial tension between the surfactant and coacervate phase have been measured using atomic force microscopy 38,54 and surface forces apparatus. 55,56 The structure and dynamics of bulk coacervates have been characterized using rheology 37,47,53,[57][58][59][60][61][62][63][64][65] along with X-ray and neutron scattering. 62,66,67 Finally, the thermodynamics of bulk coacervation has been characterized using isothermal titration calorimetry (ITC).…”

Mechanism of DNA‐Induced Phase Separation for Transcriptional Repressor VRN1

“…Salts can modulate polyelectrolyte condensation and determine the precipitate–coacervate continuum . We further studied the mechanism of PSN‐ and PSB‐mediated precipitate formation.…”

Mechanism of DNA‐Induced Phase Separation for Transcriptional Repressor VRN1

“…Salts can modulate polyelectrolyte condensation and determine the precipitate-coacervate continuum. [27][28][29] We further studied the mechanism of PSN-and PSB-mediated precipitate formation. PSN and PSB formed fiberlike precipitates with DNAinthe presence of 50 mm KCl (Figure 4a,d), close to the salt concentration in commonly used plant-tissue culture media.…”

“…[27][28][29] We further studied the mechanism of PSN-and PSB-mediated precipitate formation. [27][28][29] We further studied the mechanism of PSN-and PSB-mediated precipitate formation.…”