Effects of Chain Length on the Self-assembled Structure of Perfluoroalkyl Oligomers

Abstract

Per- and polyfluoroalkyl substances (PFASs) have unique properties, such as water- and oil-repellency, and have been used in various materials worldwide. Recently, a stratified dipole arrays model was proposed to explain the properties of PFASs comprehensively. According to this model, the aggregate structures of PFA chains, which vary depending on the chain length, are the key to understanding the unique properties of PFASs. In this study, we performed molecular dynamics simulations of the perfluoroalkyl oligomers, CF₃(CF₂)_mCF₃, to examine the aggregate structure of the monolayer. The results show that the system has disordered structures and liquid-like behavior at m = 5 and 6, while hexagonal structures and solid-like behavior at m ≥ 8. The system with m = 7 behaved as an intermediate state between these two groups. This study reinforces the importance of PFA chain length in understanding the properties of PFASs.