Dipole-driven interlude of mesomorphism in polyelectrolyte solutions.

Area of Science:

• Polymer Science
• Solution Chemistry
• Soft Matter Physics

Background:

• Polyelectrolytes typically disperse uniformly in solutions due to electrostatic repulsion.
• Standard polyelectrolyte behavior is well-established for homogeneous solutions.

Purpose of the Study:

• Investigate the unusual precipitation of poly(L-lysine) (PLL) in aqueous electrolyte solutions.
• Characterize the emergence of a mesomorphic state and an anti-polyelectrolyte effect.
• Elucidate the role of acrylate ions and zwitterionic transformation in PLL solution behavior.

Main Methods:

• Light scattering measurements to determine hydrodynamic radius (R).
• Systematic variation of ionic strength and PLL concentration.
• Analysis of scaling laws for aggregate size.

Main Results:

• Observed precipitation of positively charged PLL at low ionic strength, contrary to standard behavior.
• Identified a mesomorphic state of spherical aggregates between precipitation and homogeneous solution limits.
• Demonstrated an anti-polyelectrolyte effect where PLL hydrodynamic radius shrinks with decreasing ionic strength.
• Revealed a scaling law for aggregate radius (R) dependence on PLL concentration (c).
• Observed disassembly of mesomorphic aggregates via a self-poisoning mechanism at higher PLL concentrations.

Conclusions:

• The observed phenomena are attributed to intra- and interchain dipolar interactions.
• A transformation of polycationic PLL to a physical polyzwitterionic PLL is proposed.
• Dipole-directed assembly and the anti-polyelectrolyte effect are crucial for understanding coacervation and biomolecular condensates.