Rheological characterization of liquid-to-solid transitions in bulk polyelectrolyte complexes.

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Polyelectrolyte complexation can yield liquid or solid states.
• The transition mechanism between these states is not fully understood.
• Understanding this transition is crucial for controlling material properties.

Purpose of the Study:

• To elucidate the liquid-to-solid phase transition mechanism in polyelectrolyte complexes.
• To analyze the role of salt concentration in this transition.
• To characterize the structural changes leading to gelation.

Main Methods:

• Rheological analysis of poly(4-styrenesulfonic acid, sodium salt) (PSS) and poly(diallyldimethyl ammonium chloride) (PDADMAC) complexes.
• Application of time-salt superposition to study viscoelastic response.
• Systematic variation of potassium bromide (KBr) concentration.

Main Results:

• Rheology revealed distinct viscoelastic behaviors for liquid coacervates and solid complexes.
• Time-salt superposition enabled detailed analysis of the transition.
• Decreasing salt concentration led to increased complex water content reduction and network formation.

Conclusions:

• The liquid-to-solid transition is driven by decreasing salt concentration and water content.
• A physical gel forms at a critical salt concentration due to network percolation.
• Electrostatic interactions act as trapped crosslinks in the gel network.