A pH-Responsive Trimeric Fluorinated Quaternary Ammonium Surfactant with Recyclability and Enhanced Antimicrobial Activity

A novel trimeric fluorinated quaternary ammonium surfactant (triQA-1) was designed and synthesized featuring three short perfluorobutyl chains linked by benzyl groups. The compound exhibits exceptional surface activity with a critical aggregation concentration (CAC) of 0.11 mmol/L and surface tension at γ CAC of 18.47 mN/m, outperforming traditional perfluorooctanoic acid and perfluorooctanesulfonic acid. Notably, triQA-1 demonstrates unique pH-responsive phase separation behavior: precipitation occurs at pH 1 (recoverable) and pH 13 (salting-out), while the solution remains stable within pH 3–11. This reversible transition enables efficient recycling and controllable foaming/defoaming. Thermodynamic, TEM, and Raman analyses reveal that the acid-induced precipitation mechanism involves hydrogen bond network disruption and fluorocarbon chain aggregation, rather than conventional acid–base group ionization. Furthermore, triQA-1 exhibits superior antimicrobial activity against E. coli (MIC = 4.2 μM) and S. aureus (MIC = 0.18 μM) compared to commercial quaternary ammonium. These properties render triQA-1 a promising sustainable alternative to persistent fluorinated surfactants for applications in antimicrobial coatings and corrosion protection.