Solubilization Mechanism of Eco-Friendly Fluorocarbon Surfactants for Fluorinated Monomers: Perfluorinated Chain Length Effect and Dynamic Thermal Response

Abstract

Extremely hydrophobic fluoromonomers are highly prone to phase separation during emulsion polymerization. Overcoming macroscopic experimental limitations, this study employs all-atom molecular dynamics (AA-MD) simulations to investigate the molecular-level solubilization behavior and thermal adaptability of the novel eco-friendly zwitterionic fluorocarbon surfactant-perfluorohexyl (butyl) sulfonyl carboxy propylamino dimethyl betaine (PFSC) and the traditional hydrocarbon surfactant SDS toward the monomers tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE). Simulation results indicate that fluorinated monomers in the SDS system exhibit a more dispersed spatial distribution, with weaker local association in surfactant-enriched regions. In contrast, fluorinated monomers in the PFSC system tend to distribute within regions rich in perfluorinated segments. This spatial characteristic is consistent with thermodynamic analysis results dominated by solubility parameter matching and van der Waals interactions. Under high-temperature conditions, the perfluorohexyl sulfonyl carboxy propylamino dimethyl betaine (C6) system maintains relatively stable local spatial characteristics, with the fluorinated monomers exhibiting low migration behavior. These spatial distribution characteristics and thermal response behaviors suggest that a fluorine-rich environment may help preserve the local distribution of fluorinated monomers under high-temperature conditions. These findings provide molecular-level insights into the structure–property relationships of eco-friendly fluorinated surfactants and offer computational guidance for their rational design.