Surface Micelles of F(CF2)m(CH2)22COOH on the Aqueous Cadmium Acetate Solution Investigated in Situ and ex Situ by Infrared Spectroscopy

Abstract

Partially fluorinated alkanoic acids F(CF2)m(CH2)22COOH (m = 8, 6, and 4) spontaneously formed monodispersed nanometer-sized two-dimensional micelles on the aqueous cadmium acetate subphase in a Langmuir trough, according to the atomic force microscope images. Normal transmission and grazing incidence reflection infrared spectroscopy were applied to investigate the single monolayer deposited on solid substrates by the Langmuir−Blodgett (LB) method. Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was applied to investigate the monolayer in situ. PM-IRRAS simulation was performed for the first time to determine molecular orientation at the air/water interface. The hydrocarbon chain takes a planar trans zigzag conformation on the subphase surface, largely inclined at 43∼40° and twisted at 66∼61°, packing in a pseudotriclinic way. By contrast, the simple CH3(CH2)20COOH spontaneously forms micrometer-sized domains on the aqueous Cd2+ subphase, with the hydrocarbon chain verticall...