A Coarse-Grained Model Describing the Critical Micelle Concentration of Perfluoroalkyl Surfactants in Ionic Aqueous Phase

In this study, dissipative
particle dynamics (DPD) simulations
were employed to determine the critical micelle concentration (CMC)
of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in ionic aqueous
solutions. This approach provides precise CMC data for PFAS surfactants
in the presence of various ionic species, thereby addressing a gap
in the current literature. Additionally, this study contributes to
the development of open-source molecular force fields for charged
perfluorinated compounds, which are currently limited. These models
incorporate hydration free energy values obtained from density functional
theory (DFT) and account for ionic interactions through a well-established
linear relationship. Hydrophobic interactions between the surfactant
tail and water were fine-tuned to match the CMC of chosen surfactants.
Then, the DPD models successfully predicted CMC values for a diverse
range of surfactants, including those based on hydrocarbons and PFAS,
demonstrating the ability to represent realistic salinities encountered
in natural waters. Experimental validation of the methodology was
conducted using sodium n-nonyl sulfate (SNS) and
sodium n-dodecyl sulfate (SDS) via interfacial tension
measurements, confirming the accurate representation of the CMC changes
with salinity. This study enhances our understanding of the behavior
of PFAS surfactants in ionic aqueous solutions and provides a valuable
tool for predicting CMC values in complex environmental systems.