Adsorption behavior and structural characterization of azo dyes on a Langmuir-Blodgett film of octadecylamine

The adsorbability of the Langmuir-Blodgett (LB) film of octadecylamine (ODA ) has been investigated using a-naphthol orange (NO) and methyl orange (MO) as adsorbates. It was found that the specific adsorptions of these azo dye s occurred on the ODA LB film predominantly by ionic interaction, and also that the adsorption behavior depended on pH according to the ionic states o f NO and MO as well as that of the ODALB film. The structural characteristi cs of the LB films such as orientation, layer-layer distance, and topograph y of the film surface have been evaluated by means of FTIR and W-vis spectr oscopies, X-ray diffraction in the low-angle region, and atomic force micro scopy (AFM), respectively. The results obtained indicated that the adsorpti on of dyes induced rearrangements of the layer structure, where the hydroca rbon chains took an interdigitated structure and the dye molecules in the L B film exhibited remarkable distinction in the adsorbing state, i.e., a lie -flat configuration of NO and an edge-on configuration of MO.