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J. Umemura, S. Takeda, T. Hasegawa, T. Kamata, and T. Takenaka
[Spectrochimica Acta, Vol.50A, No.8/9, pp.1563-1571, 1994]
Langmuir-Blodgett (LB) films of Cd and Ca stearates with 1, 3, 9, and 21 monolayers were fabricated on silver-coated glass slides. 9-Monolayer LB films of Cd and Ca salts of deuterated stearic acid, in which the 1st, 5th, or 9th layer was replaced by 1 monolayer of undeuterated analogues, were also prepared on the above substrates. Temperature dependences of Fourier transform infrared (FT-IR) reflection-absorption (RA) spectra were examined for these LB films in the range 31-140C°. At room temperature, the hydrocarbon chains in these LB films were in a well-ordered state with a high degree of perpendicular orientation to the substrate. However, they became disordered at elevated temperatures. These order-disorder phase transition temperatures were dependent on the film thickness, to a small degree in the Cd stearate LB film (102-108C°), but to a large degree in the Ca stearate LB film (103-129C°). In the latter LB film, the effect of dehydration was inferred. The degree of disorder at high temperatures was dependent on the film thickness and the location of monolayer in the 9-monolayer LB films. This result is discussed in terms of the internal pressure within the LB film.