Quantitative Estimation of Molecular Orientation in Langmuir-Blodgett Films of Octadecyldimethylamine Oxide and Dioctadecyldimethylammonium Chloride

The molecular orientation in the Langmuir-Blodgett (LB) films of octadecyldimethylamine oxide (C(18)DAO) and dioctadecyldimethylammonium chloride (2C(18)DAC) was estimated by a newly proposed calculation method for the infrared reflection-absorption (RA) spectral data. The Y- and X-type multilayer LB films of both compounds were prepared respectively as LB(Y) and LB(X) for the RA measurements. There found a large difference in thermal stability between the LB(Y) and LB(X) films for both compounds. Above all, the 9-monolayer LB(Y) films showed a structurally heterogeneous property. explored by introducing a new analyzing method. The method revealed that the first monolayer directly deposited on a gold surface had a specific molecular structure arising from the interaction with the substrate. The structure is different from that in the rest layers. The LB(X) films were found to be thermally very stable; the thermal recovery was notably good comparing to the LB(Y) films.