Perfluorinated Alcohols Induce Complex Coacervation in Mixed Surfactants

Area of Science:

• Colloid and Surface Science
• Supramolecular Chemistry
• Materials Science

Background:

• Coacervation is a liquid-liquid phase separation phenomenon crucial in various biological and synthetic systems.
• Mixed cationic-anionic (catanionic) surfactants are known to form complex structures in solution.
• Fluorinated alcohols, like HFIP, exhibit unique solvation properties.

Purpose of the Study:

• To investigate the novel biphasic separation in aqueous solutions of mixed catanionic surfactants induced by hexafluoroisopropanol (HFIP).
• To characterize the chemical composition and phase behavior of the resulting coacervate phases.
• To understand the role of HFIP in driving coacervation and contrast it with aliphatic alcohols.

Main Methods:

• Preparation of mixed surfactant solutions (CTAB/SDS and DTAB/SDS) with varying concentrations and mole ratios.
• Induction of coacervation using hexafluoroisopropanol (HFIP).
• Phase behavior analysis and chemical composition determination of aqueous-rich and coacervate phases (HFIP, water, surfactant concentrations).

Main Results:

• HFIP induces coacervation in CTAB-SDS and DTAB-SDS mixtures, with DTAB-SDS requiring equimolar ratios.
• The surfactant-rich coacervate phase is enriched in HFIP and surfactants, with low water content.
• Water concentration in the coacervate phase increases with total HFIP, leading to phase growth, while HFIP concentration remains relatively constant.
• Counterions (Br-, Na+) predominantly stay in the aqueous phase, suggesting ion-pairing of surfactants in the coacervate.

Conclusions:

• HFIP acts as a potent inducer of coacervation in catanionic surfactant systems.
• The observed increase in water content with HFIP concentration is a key factor in coacervate phase growth.
• HFIP's unique interactions drive specific ion-pairing and phase separation, distinct from aliphatic alcohols like isopropanol.