Neutron Reflectivity Study of Interface between Water and Polymer with SF₅ Groups and its Hydrophobicity

Abstract

  Conventional hydrophobic surface is composed of perfluoroalkyl units including trifluoromethyl groups. Pentafluorosulfanyl group with five fluorine atoms is suspected to be a candidate of hydrophobic functional groups, comparable to trifluoromethyl group. Herein, polymers with pentafluorosulfanyl, trifluoromethyl, methyl and hydrogen groups in their side chains were synthesized and their thin films were fabricated by the spin-coating methods. Their surface free energies were evaluated from the dynamic contact angles on their polymer surfaces. The polymer thin film with pentafluorosulfanyl groups possessed the lowest surface free energy in the synthesized polymers. From the neutron reflectivity measurements of the polymer thin films in water, the affinity of polymers toward water was investigated. The thin films without hydrophobic fluorine groups in water formed swollen layers at top surface regions, while no swollen layer was observed in the thin film of polymer with pentafluorosulfanyl groups. This suggested that pentafluorosulfanyl group possessed low affinity toward water, which corresponded to high hydrophobic properties of the polymer with pentafluorosulfanyl groups. It was concluded that pentafluorosulfanyl groups were promising hydrophobic functional groups.