Effects of the Rigid Benzene Ring Spacer Group on the Thermal Stability, Surface Activity and Aggregation Behavior of Quaternary Ammonium Salt Cationic Fluorocarbon Surfactants

Abstract

Traditional long-chain perfluoroalkyl surfactants such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) have been restricted from production and use in many countries due to their high biotoxicity, poor biodegradability, and high environmental mobility. Constructing novel fluorocarbon surfactant structures is one of the effective means of developing their alternatives. To this end, we herein prepared a novel fluorocarbon surfactant (BHFB) and compared its performance with that of a structurally analogous fluorocarbon surfactant (WTFB). The results indicate that BHFB with a rigid benzene ring structure exhibits superior surface activity. This is attributed to the π-π stacking interaction of the benzene rings, which enables BHFB to arrange more tightly at the air-liquid interface. Consequently, BHFB exhibits lower surface tension and critical micelle concentration (CMC) (γ_CMC = 17.07 mN/m, CMC = 1.098 × 10^–5 mol/L). Moreover, the introduction of the rigid benzene ring structure also improves the physicochemical properties of BHFB, such as thermal stability, aggregation behavior, wettability, and foam stability. In contrast, WTFB without a benzene ring structure is weaker than BHFB in all performance aspects. This work provides further insight into the structural design of novel eco-friendly fluorocarbon surfactants.