Stimuli-Induced Nonequilibrium Phase Transitions in Polyelectrolyte-Surfactant Complex Coacervates

Area of Science:

• Soft matter physics
• Colloid science
• Materials chemistry

Background:

• Polyelectrolyte-surfactant complexes (PESCs) are crucial soft colloids with diverse applications.
• Understanding PESC behavior under nonequilibrium conditions is increasingly important.
• Previous studies often focused on pseudoequilibrium conditions within micellar or vesicular regions.

Purpose of the Study:

• To investigate the structural changes of PESCs under nonequilibrium conditions by crossing phase boundaries.
• To explore the effect of rapid pH variation on surfactant-polyelectrolyte systems.
• To demonstrate the use of microbial glycolipid biosurfactants in developing sustainable PESCs.

Main Methods:

• Utilized two microbial glycolipid biosurfactants with polyamines, responsive to pH.
• Induced rapid, continuous pH variation to cross micelle-vesicle and micelle-fiber phase boundaries.
• Analyzed phase behavior and structural transitions of the resulting PESCs.

Main Results:

• Complex coacervates (Co) consistently formed in the micellar region, dictating PESC stability and structure.
• A glycolipid forming single-wall vesicles showed a transition from complex coacervates to multilamellar walls vesicles (MLWV).
• The fiber-forming glycolipid's complex coacervate disassembled into free polyelectrolyte and the equilibrium fiber phase.

Conclusions:

• Nonequilibrium pH-driven transitions significantly alter PESC structures.
• Microbial glycolipid biosurfactants offer a sustainable route for creating novel PESCs.
• The observed phase behaviors provide insights into soft colloid self-assembly and stability.