THERMAL-BEHAVIOR OF LANGMUIR-BLODGETT-FILMS .3. STRUCTURE AND EPITAXIAL LAYER GROWTH OF STEARIC, ARACHIDIC AND BEHENIC ACID MULTILAYERS

The bilayer spacings and morphology of stearic, arachidic and behenic acid bulk samples and Langmuir-Blodgett multilayers have been investigated by X-ray diffraction, atomic force microscopy and reflection polarized microscopy. The molecular ordering in the bulk volume samples is identical to that of the Langmuir-Blodgett multilayers. In the as-prepared samples the coexistence of three homologous forms is found, consisting of stacks of uniform molecular tilt of almost-equal-to 21-degrees, almost-equal-to 28-degrees and almost-equal-to 36-degrees. The stacks (domains) have lateral dimensions of typically 1 mum. The samples can be annealed thermally into the most tilted phase with large domains (typically 100 mum) of equal tilt angle but different tilt orientation. The film thickness profiles of all samples typically show bilayer steps, the annealed multilayer samples having much smoother surfaces than the untreated films. The structure and preparation of the floating precursor monolayer hardly influences the molecular ordering of the resulting multilayer. The molecular packing and the stackwise growth of layers of uniform molecular tilt are caused by intermolecular and layer/layer interactions. These layer/layer interactions however, are not strong enough to induce strict overall uniform layer ordering. Multilayers deposited onto supports of uniform molecular tilt (annealed multilayers) disintegrate into stacks of three different tilt angles.