Infrared spectroscopic study on thermal behavior of Langmuir-Blodgett films of octadecyl ammonium octadecanoate and octadecylammonium octadecanoate-d35

Langmuir-Blodgett (LB) films of octadecylammonium octadecanoate (C(18)H(37)j7NH(3)(+)C(17)H(35)COO(-),ODASA) and octadecylammonium octadecanoate-d(35) (C18H37+NH3+C17D35COO-, ODASA-d(53)) were prepared and their thermal behaviors were investigated by variable-temperature Fourier transform infrared transmission spectroscopy. It was found that the two hydrocarbon chains of ODASA molecule in LB films are highly ordered while that protonated (H) chain in ODASA-d(35) is partially disordered with some gauche conformers introduced at room temperature. The thermal stability of ODASA-d35 in LB films is also different from that of ODASA. The two hydrocarbon chains in ODASA LB films show one sharp order-disorder transition with temperature increasing from 85 to 90 `degrees C. But in ODASA-d35 LB films, the protonated and deuterated chains show quite different thermal behavior, respectively. For example, the protonated chains undergo order-disorder transition between 80 and 90 degrees C, abruptly from 80 to 85 degrees C, while the phase transition of the deuterated ones undergoes slowly and persists long time from 70 to 85 degrees C. (C) 2007 Elsevier B.V. All rights reserved.