Substrate and chain length dependencies of the thermal behavior of [CF3(CF2)(m)(CH2)(n)COO](2)Cd single monolayers investigated by infrared reflection absorption spectroscopy

Temperature-variable grazing incidence reflection absorption (GIR) spectra were recorded for the single monolayer of [CF3(CF2)(m)(CH2)(n)COO)](2)Cd [( m,n)=(7,10), (7,16), (7,22), (5,22), and (3,22)], transferred from aqueous Cd2+ subphase to gold- and aluminum-evaporated glass substrates. The spectr a reveal that these monolayers have better thermal stability on Al substrat es than on Au. An "interaction band" is identified at 1484 similar to 1480 cm(-1), due to the nu (s)(COO-) mode of carboxylate headgroups in ionic bon ding with the Al surface. It is found that both the van der Waals interacti on between the trans zig-zag hydrocarbon chains and the overlapping interac tion between the fluorocarbon helixes are responsible for the systematic va riation of the monolayer thermal behavior with (m,n). The thermal behavior of a single monolayer of cadmium stearate, serving as a model system, has b een investigated to further confirm the spectral interpretation about the p artially fluorinated monolayer. In addition, temperature-dependent friction measurements show that the single monolayers of (m,n)=(7,16), (7,22), (5,2 2), and (3,22) are potential molecular lubricants that can be used in the r ange of 25 similar to 140 degreesC. (C) 2001 American Institute of Physics.