Why can a hydrophilic polyelectrolyte precipitate and redissolve below the critical micelle concentration of an oppositely-charged surfactant ?

• DOI: 10.48550/arxiv.2411.06355
• Publication Date: 2024-11-09
• Authors: Huaisong Yong
• Keywords: Thermodynamics of micellization

We theoretically study the reentrant condensation of a polyelectrolyte in presence an oppositely-charged surfactant,a phenomenon whose phase-transition mechanism remains under discussion. focus on adsorption and attraction effects surfactant near/on polymer chains, ignore their own non-essential mixing if molecules are far away from chains. This approach allows us to construct simple mean-field theory solve it analytically, finally rationalize essential features (such as "egg shape" spinodal phase diagrams) induced by diluted surfactants. By theoretical analysis, we found that strong electrostatic between ionic monomers ions is critical understand peculiar both collapse reentry transitions polyelectrolytes can occur when concentration lower than its bulk micelle (CMC). The analytical solution indicates minimum coupling energy for nonlinear hydrophobic-aggregation effect adsorbed transition occur,which explains why show only chain length longer length. obtained results will shed light deep understanding liquid-liquid separation biological systems where surfactant-like proteins/peptides bound bio-polyelectrolytes play important role.