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Crystal formation and growth in Langmuir-Blodgett multilayers of azobenzene derivatives: optical and structural studies

Thin Solid Films
Publication Date
DOI: 10.1016/0040-6090(85)90117-8


Abstract Langmuir-Blodgett (LB) multilayers have been prepared from some azobenzene derivatives which show liquid-crystalline bulk behaviour. The newly prepared films were transparent, amorphous and isotropic by polarized light microscopy but, when the temperature was increased, crystalline regions were observed to grow until the films were fully crystalline with birefringent domains of uniform orientation up to 2 mm across. The area per molecule, total thickness and X-ray diffraction peaks indicate that the films have a close-packed layer structure which is essentially unaltered by the crystallization process. The factors affecting domain size and orientation, predominantly film thickness, dipping direction and substrate, are described. Evidence is presented that, with a previously crystallized multilayer as substrate, crystallization of further deposited layers was spontaneous and epitaxial, but other crystalline substrates investigated had no ordering effect. A polymeric derivative of one of the materials formed uniform LB multilayers but did not crystallize. The results provide new insight into the factors affecting domain size, orientation and quality in LB films generally and are particularly relevant for possible optical applications of similar materials.

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