Origin of the In-Plane Anisotropy in Langmuir-Blodgett Films

Abstract

An extended model of flow orientation has been developed for analyzing the inplane anisotropy in Langmuir-Blodgett (LB) films by taking into account the viscoelastic nature of a condensed monolayer at the air-water interface as a Bingham plasticity. The model is based on a two-dimensional fluid and a line-sink as representing the monolayer and the substrate, respectively. The predictions from the present model with respect to the dichroic behavior have been experimentally verified employing a mixed LB system of a merocyanine dye and a fatty acid. The model is also consistent with the remarks from ESR line-shape analysis reported previously and those from analysis of the optical absorption spectra using the extended dipole theory. These results show that the inner stress due to the velocity gradient in the monolayer during the deposition is the origin of the in-plane anisotropy.