Preparation of Oriented Multilayers of Poly(silane)s by the Langmuir-Blodgett Technique

Abstract

The spreading behavior of poly(silane)s at the air-water interface of a Langmuir trough was investigated. Force-area diagrams of poly(silane)s with various side groups and different molecular weights were recorded. Stable monomolecular layers were not obtained for alkyl substituents. In the case of p-alkoxy-phenyl and, even better, m-alkoxyphenyl residues attached to the silicon backbone, stable monolayers were obtained that could be transferred to solid hydrophobic substrates by applying the Langmuir-Blodgett technique. These transferable poly(silane)s have a rodlike shape and form dense rafts at the water surface. Multilayers consisting of up to 600 monolayers of this raftlike structure with the rods preferentially oriented into the dipping direction have been obtained. The order parameter describing the degree of orientation of the rods with regard to the dipping direction was determined from the dichroic ratio of the band of the silicon-silicon chromophores at 397 nm for the m-alkoxyphenyl-substituted poly (silane). The order parameter could be improved substantially by annealing the samples subsequent to deposition of the layers at temperatures up to 150 °C. Samples thus obtained have the character of a monodomain nematic liquid crystal of molecularly defined thickness. Details of the structure were further elucidated by X-ray reflection and polarized IR spectroscopy. © 1991, American Chemical Society. All rights reserved.