WETTABILITY, SURFACE-MORPHOLOGY, AND STABILITY OF LONG-CHAIN ESTER MULTILAYERS OBTAINED BY DIFFERENT LANGMUIR-BLODGETT DEPOSITION TYPES

Methyl arachidate Langmuir-Blodgett multilayers, built up by X-, XY- and Y-type transfers, are characterized by means of contact angle measurements, and optical and atomic force microscopy under ambient conditions. Contact angle investigation shows identically high hydrophobicity of the surfaces produced by X- and Y-type depositions, implying molecular overturning during the X-type transfer. This overturning has not been detected in the previous X-ray study of small numbers of deposited fatty acid methyl ester monolayers. Molecular resolution AFM images of thin methyl arachidate LB films show a disordered surface structure. Scanning over larger film regions reveals a considerable difference in the surface morphology, corresponding to pure and mixed-type LB transfers. Reorganization of the multilayers occurs under ambient conditions in both cases. Larger aggregates, steps, and irregular islands are found with Y-type deposition. Ester LB films studied in an aqueous environment rearrange more easily than those stored in air. AFM imaging of the ''contact line corrosion'' of the multilayers shows a collective depletion of the whole LB film from the substrate at the wetting perimeter. The instability of the ester mono- and multilayers is explained on the basis of the intra- and interlayer molecular interactions within the spread and the deposited films, and by their weak adhesion to the substrate.