Preparation of Langmuir−Blodgett Mono- and Multilayers of Copolymers of Isocyanides with NLO-Active Side Chains. Effect of a Spacer Group between the NLO Chromophore and the Polymer Backbone

Preparation and characterization of polyion-complexed Langmuir-Blodgett films containing an NLO chromophore

Polyion complexes formed by monolayers of quaternary ammonium amphiphiles containing the 4-nitro-4'-alkoxy azobenzene chromophore spread at the surface of aqueous solutions of a number of anionic polyelectrolytes were investigated. In general, pi-A isotherms were found to depend on the nature of the polyion present in the subphase, with monolayers of complexes involving polycarboxylates tending to exhibit larger limiting areas than those formed with polysulfonates or polysulfates. Monolayers of the polyion complexes can be transferred to hydrophilic solid substrates to yield Z-type LB films, although some peeling off for more than 10 layers is an impediment. X-ray reflectivity measurements indicate that relatively smooth and uniform films are obtained up to about 10 layers. Average layer thicknesses are, however, significantly smaller than extended molecular lengths, implying that the amphiphiles are strongly inclined from the surface normal. Polarized FT-IR measurements also indicate poor molecular orientation perpendicular to the surface. Preliminary SHG measurements for LB films of two systems, 12Q/CMC-Na and 12Q/PAA, confirm the presence of noncentrosymmetric out-of-plane chromophore ordering. Stable signals are observed for elevated temperatures up to 130 degrees C and for a period of 4 months at room temperature. To the best of our knowledge, this represents the first report of stable SHG in LB films of polyion complexes.

Formation and Orientation Studies of a Z-Type Polymeric Langmuir-Blodgett Film

Langmuir-Blodgettfilms of poly(acrylonitrile-co-4-vinylpyridine) were assembled on quartz and calcium fluoride substrates from a preformed monolayer on water. The observed transfer ratios indicated z-type deposition. Infrared spectroscopic measurements in the transmission mode revealed a linear dependence of the nitrile absorbance as a function of the number of layers deposited. Polarized infrared spectroscopy was used to semiquantitatively determine the average chain orientation in the film. Calculations of dichroic ratios indicate that the chains lie relatively flat on the substrate surface. Polarized ultraviolet spectroscopy was also utilized to determine the orientation of the pyridine headgroups in the LB film, and the calculations indicated a pyridine tilt angle of approximately 19 degrees to the film surface. Copyright 1999 Academic Press.