PHOTOREACTIVE LANGMUIR-BLODGETT-KUHN MULTILAYER ASSEMBLIES FROM FUNCTIONALIZED LIQUID-CRYSTALLINE SIDE-CHAIN POLYMERS .2. STRUCTURAL CHARACTERIZATION OF HOMOPOLYMERS AND COPOLYMERS CONTAINING AZOBENZENE AND PHENYLBENZOATE MOIETIES

Liquid crystalline side chain polymers containing photoreactive azoben zene chromophores in the dark-adapted trans form and phenylbenzoate gr oups as co-mesogens have been prepared and investigated as monomolecul ar layers at the water/air interface and as multilayer assemblies depo sited onto solid supports by the Langmuir-Blodgett-Kuhn (LBK) techniqu e. Pressure area isotherms at variable temperatures together with refl ection absorption spectra and Brewster angle microscopic pictures have been taken and analyzed i) to derive information about the structural order and the packing properties of the mesogenic side groups within the monolayers of different homo- and co-polymeric systems and ii) to optimize the conditions for the transfer of the monolayers. The result ing multilayer assemblies were primarily characterized by X-ray reflec tometry studies, which yield the film thickness, the electron density modulations indicative of any internal (double) layer periodicity, and two roughness parameters characterizing the substrate/film and the fi lm/air interfaces, respectively. These investigations were complemente d by surface plasmon, UV-vis and IR spectroscopic measurements which p rovided further information as to the optical/structural properties of the samples. It was found that those systems containing only azobenze ne side groups (or a high percentage of them) are composed of metastab le double layer subunits which can be easily assembled to thicker film s even capable of carrying waveguide modes. The azobenzene chromophore s forming various types of aggregates have an average tilt angle of 36 0 relative to the film normal presumably with a broad angular distribu tion. If the azobenzene mesogens are diluted by phenylbenzoate co-meso gens in the ratio 1:2, only the first few dipping cycles show a good m onolayer transfer so that only thin multilayer assemblies can be built up. Moreover, all these preparations though deposited in the Y-type m ode show no indication of a doublelayer structure in the transferred f ilm, but instead exhibit the so-called mesogen peak with a smectic per iodicity corresponding to only a single monolayer. A structural model with interdigitating side groups is proposed to account for these expe rimental results.