Langmuir-Blodgett Film of Amphiphilic C₆₀Carboxylic Acid Dependence

M. Matsumoto, H. Tachibana, R. Azumi, Motoo Tanaka, Takayoshi Nakamura, G. Yunome, M. Abe, S. Yamago, and E. Nakamura
[Langmuir, Vol.11 pp.660-665, 1995]

An amphiphilic C₆₀molecule (am C₆₀) with a substitute having a hydrophilic carboxylic group at the end was found to form a monolayer at the air - water interface and the structure of the Langmuir - Blodgett (LB) film (Z-type) was elucidated. The shortest distance between the C₆₀was estimated to be 0.95 nm using a limiting area per molecule of 0.78 nm² at the air - water interface, assuming the close packing of the C₆₀moiety in two dimensions. Adjacent C₆₀moieties have an electronic interaction which was shown in the red-shift of the characteristic bands in the UV/vis absorption spectrum of the LB film compared with that of a solution spectrum. Several lines of evidence suggested that the molecule has an oblique orientation in the LB film and exists in a pairwise manner due to the dimer formation of the carboxylic groups within a monolayer, not between the adjacent monolayers. The AFM observations revealed that the surface of a single-layer LB film, which consists of domains of ca. 0.1 mum in diameter, is rather smooth and that the undulation is ± 1 nm for most of the surface except for defects such as vacancy and bilayer regions. The area fractions of the monolayer, the vacancy, and the bilayer regions were estimated to be 88 ± 7, 7 ± 5, 5 ± 3%, respectively. The layer structure was also confirmed using X-ray diffraction analysis which indicates the repeat distance of ca. 2.6 nm along the surface normal of the multilayer LB film. The structural model of the multilayer LB film is shown in Fig. 1.

Fig. 1. Structural model of the multilayer LB film of amC₆₀