Langmuir-Blodgett Film Stability Via Atomic Force Microscopy

Abstract Langmuir-Blodgett (LB) films of fatty acid salts are inherently unstable due to the fundamental incompatibility of the asymmetric monolayer film transferred from the water surface with the centrosymmetric equilibrium form of the fatty acid bulk crystal. One consequence of this incompatibility is that fatty acid salt films deposited by the LB technique do not remain as flat and uniform films, but reorganize into bilayer step islands. By using mixed chain length films, the islands and holes had distinct heights that suggest this reorganization occurs by a bulk folding of the layers rather than a molecular reorganization of the molecules. We have studied cadmium arachidate (CdA) LB films, varying the substrate used, the number of layers deposited, and the time the film spends under the aqueous subphase. All films were imaged in air with an Atomic Force Microscope (AFM).