Surface Activity, Wettability, and Foamability of Short-Chain C4-Based Carboxyamide Fluorinated Cationic Surfactants

Long-term use of widespread legacy fluorinated surfactants has certainly set an environmental footprint due to their persistence, bioaccumulation, and toxicity. However, their surface activity remains unmatched, calling for the need for potential substitutes that exhibit parallel surface performance ever since legislative rules were implemented. Through this work, we present the synthesis of shorter fluorinated chain-based carboxyamide surfactants having a C4 fluorocarbon group. Two cationic surfactants with homologous groups at the quaternary ammonium position of the surfactant structure were synthesized and characterized using ¹H, ¹³C, and ¹⁹F NMR, and IR spectroscopy. The surface activity of the surfactants was analyzed. They showed a lowering in surface tension of up to 19 mN m^-1 at critical micelle concentrations ranging from 7 to 12 mmol L^-1, as determined using the du Noüy ring method. Their dynamic surface tension, indicating the time-dependent behavior of surfactants in solution, was also determined. The micelle aggregates were characterized for size and morphology using DLS and TEM. Further, the application of surfactants was explored for foaming and wetting. Both surfactants demonstrated promising results, reducing the contact angle on the hydrophobic PTFE surface to 10-12° within 120 s. Overall, the surfactants are prospective alternatives to the legacy long-chain fluorinated counterparts and offer applications in firefighting and coating domains.