Surface activity of perfluorodecanoyl end-capped poly(ethylene oxide) and associated adsorption behavior to the air–water interface

Abstract

The structure and adsorption kinetics of poly(ethylene oxide) end-capped with perfluorodecanoyl groups either at one or both ends have been characterized. These nearly monodisperse polymers with molecular weights in the range of 400–16 K g/mol are effective nonionic surfactants with very high surface activity. For aqueous solutions with concentrations in the range of 2–8 mg/ml, surface tensions determined by the drop-volume method are as low as 13.6– 18.0 mN/m at 20°C. At high surface coverage, close-packed PEO chains with one end capped form a brush-like structure at the interface. Polarized infrared reflectance spectroscopy showed that perfluoroalkyl groups were nearly perpendicular to the air–water interface. The molecular area per chain was 30–32 Å 2 for poly(ethylene oxide) capped only at one end and 36–40 Å 2 for poly(ethylene oxide) with both ends capped. Only 22% of poly(ethylene oxide) chains with both ends capped form loops at the interface, while the remaining chains form an extended structure at high surface coverage.