Dilution induced coacervation in polyelectrolyte-micelle and polyelectrolyte-protein systems

Area of Science:

• Supramolecular Chemistry
• Polymer Science
• Colloid Science

Background:

• Self-suppression, the instability of complex coacervates at high concentrations, is a known phenomenon in polycation-polyanion systems.
• The transient nature of these complexes hinders the development of robust theoretical models.
• Stable polyelectrolyte-micelle and polyelectrolyte-protein complexes serve as valuable coacervate precursors.

Purpose of the Study:

• To investigate the mechanism of dilution-induced coacervation (DIC).
• To characterize the structural changes of coacervate precursors upon dilution.
• To challenge existing models of complex coacervation by studying stable precursor systems.

Main Methods:

• Formation and characterization of stable poly(diallyldimethylammonium chloride) (PDADMAC) complexes with mixed micelles (SDS/TX100) and bovine serum albumin (BSA).
• Observation of liquid-liquid phase separation upon isoionic dilution.
• Analysis of complex size changes using hydrodynamic radius (R_h) measurements.

Main Results:

• Liquid-liquid phase separation was observed upon isoionic dilution, consistent with self-suppression.
• Dilution-induced coacervation (DIC) involved a decrease in complex size, from R_h∼100 nm to R_h≤30 nm for polyelectrolyte-micelle complexes.
• Polyelectrolyte-protein complexes showed less significant size reduction (50 nm to 35 nm) and are unlikely to be net neutral.

Conclusions:

• Stable coacervate precursors exhibit dilution-induced coacervation (DIC), providing a new avenue for modeling.
• DIC involves the dissociation of large inter-macromolecular complexes into smaller intra-polyelectrolyte complexes.
• The observed size changes and charge characteristics challenge the notion of near-neutrality in complex coacervation.