Solid-to-Liquid Phase Transition in Polyelectrolyte Complexes

Abstract

Strongly interacting polyelectrolyte complexes (PECs) are known to form solid precipitates that can transform into liquid droplets upon the addition of salt to break intrinsic ionic associations. However, the origin of this phase transition and the molecular details of what constitutes a solid complex remain poorly understood. Here, we study comprehensively the salt-driven solid-to-liquid phase transition of a model symmetric PEC system formed by two styrenic polyelectrolytes, from the perspectives of dynamics, phase behavior, and internal structures. In the salt-free state, rheological and thermogravimetric measurements revealed that this PEC appeared to be a soft solid comprising 90 % water by weight. However, with progressive addition of up to 2.0 M NaBr salt, it surprisingly stiffened from around 103 to 105 Pa in modulus and expelled water into the supernatant. Using small-angle X-ray scattering and cryogenic transmission electron microscopy, we determined that the counterintuitive salt-stiffening and water loss behaviors can be ascribed to the structural evolution of polyelectrolyte chains in the complex phase, in which salt doping loosened tightly coiled and highly solvated clusters of spherical aggregates and exposed otherwise-hidden hydrophobic domains. At an approximate 2.5 M NaBr threshold, the PECs transformed into a viscoelastic liquid, and polyelectrolyte chains rearranged into more homogenous ladder-like structures. In the liquid regime, further salt addition enabled faster chain relaxation and slightly softened the materials. The breadth of material properties accessed in this versatile, charge-driven system gives new predictive insights into how to harness better ionic and chemical attributes toward physical performance in functional PEC materials. File list (2) download file view on ChemRxiv Manuscript.pdf (11.03 MiB) download file view on ChemRxiv Supplementary.pdf (4.43 MiB)

Liquid–Liquid Phase Separation of the Green Mussel Adhesive Protein Pvfp‐5 is Regulated by the Post‐Translated Dopa Amino Acid

“…Increasing the NaCl concentration of the solution resulted in larger microdroplets due to a stronger electrostatic screening, which decreases the electrostatic repulsion between the Pvfp‐5‐Dopa coacervate microdroplets and promotes their coalescence. [ 33 ] To enhance the visualization of Pvfp‐5‐Dopa microdroplets, we added 0.1 mg of green fluorescent protein (GFP) to the 90 µL of buffer solution (pH 7.5 with 1 m NaCl) and mixed with 10 µL of 1 mg mL −1 of Pvfp‐5‐Dopa to reach a final concentration of 0.1 mg mL −1 to induce phase separation. The microdroplets exhibited a strong green fluorescent signal (Figure 3e), further confirming that the incorporation of Dopa to Pvfp‐5 led to LLPS, with a capability to recruit client molecules such as GFP.…”

Spatiotemporal Formation and Growth Kinetics of Polyelectrolyte Complex Micelles with Millisecond Resolution

“…We hypothesize that this additional kinetic step arises because of the strongly charged PSS polyanion based on our previous report using PEO−PVBTMA and PEO−PSS. 42 Direct comparison of the homopolymer PVBTMA/PSS 43 and PVBTMA/PAA reveals solid and liquid complexes, respectively, by optical microscopy and SAXS (Figure S-5), which may account for key differences in the initial pairing step.…”

Conjugated Polyelectrolyte‐Based Complex Fluids as Aqueous Exciton Transport Networks

“…[33][34][35][36] However, this trend of increasing polymer concentration with increasing [salt] has been reported for solid complexes formed from hydrophobic polyelectrolytes, and was attributed to Donnan effects associated with the osmotic pressure of the salt ions. [32] It is unclear from our data whether the observed plateau in the polymer concentration is indicative of a so-called open phase boundary reported for more hydrophobic polymers, where no critical point exists, or if the more traditional self-suppression regime of coacervation was merely not observed in our experiments. [37] Next, we collected photoluminescence (PL) microscopy images to visualize the phase microstructure.…”

“…This “self suppression” phenomenon is typically associated with increased electrostatic screening at high ionic strength and higher water content in the dense phase [33–36] . However, this trend of increasing polymer concentration with increasing [salt] has been reported for solid complexes formed from hydrophobic polyelectrolytes, and was attributed to Donnan effects associated with the osmotic pressure of the salt ions [32] . It is unclear from our data whether the observed plateau in the polymer concentration is indicative of a so‐called open phase boundary reported for more hydrophobic polymers, where no critical point exists, or if the more traditional self‐suppression regime of coacervation was merely not observed in our experiments [37] …”