Monodispersed two-dimensional nanoclusters of CF3(CF2)3(CH2)22COOH on the aqueous Cd2+ subphase investigated by polarization modulation infrared spectroscopy

Polarization modulation infrared reflection absorption spectroscopy was applied to investigate two-dimensional nanoclusters of CF3(CF2)3(CH2)22COOH (C27F9) on the aqueous Cd2+ subphase in a Langmuir trough at 288 K. The –(CH2)22– long axis was always inclined on the subphase and had triclinic parallel packing with compression from 0.60 to 0.30 nm2. In contrast, behenic acid, without the CF3(CF2)3– tail, formed orthorhombic micrometer domains on the Cd2+ subphase with its hydrocarbon chain vertically aligned. It is concluded that the steric hindrance imposed by the bulky CF3(CF2)3– tail is responsible for the specific orientation and packing of the –(CH2)22– part as well as the formation of the nanometer-size clusters.