Comparison of adsorption characteristics of methyl orange and α-naphthol orange molecules onto the cationic Langmuir-Blodgett films

The adsorbability of dicationic Langmuir-Blodgett (LB) film, which was fabricated by film materials of N,N'-omega-p-xylylenebis(stearyldimethylammonium chloride) (XSAC), have been investigated by using dye molecules such as methyl orange (MO) and alpha-naphthol orange (NO) as adsorbates. The structural characterizations of these LB films before and after dye adsorption were also carried out by applying spectroscopic methods and X-ray diffraction analysis. As a result, it was found that dye molecules in the dye-adsorbed XSAC LB film exhibited the remarkable distinction in the adsorbing state, i.e., an edge-on structure for the MO molecule and a lie-flat structure for the NO molecule. Such molecular arrangements were almost the same as those of corresponding XSAC-dye complexed LB films, which was deposited from XSAC monolayers on the aqueous dye solutions. Furthermore, the dye adsorption of MO and/or NO occurred with the nearly stoichiometrical ratio of XSAC to dye in XSAC LB films, similar to the case of tristearylmethylammonium chloride (TSAC) to dye in TSAC LB films. (C) 1997 Elsevier Science S.A.