Orientational order of Langmuir–Blodgett films as determined by fluorescence anisotropy

Abstract

The orientational order parameters 〈P2〉 and 〈P4〉, of cadmium stearate Langmuir–Blodgett multilayers have been calculated from steady state fluorescence anisotropy experiments. It has been shown that it is valid to model the polarization components using the assumptions that the fluorescent probes are axially symmetric, the film is azimuthally symmetric within the plane, and that the rotational motion is slow enough to be neglected. Although the data do not preclude a dependence of anisotropy on thickness, within the sample-to-sample variations, there is no significant effect of thickness on orientational order. The order parameters for newly deposited films are 〈P2〉=0.33 and 〈P4〉=0.02. The orientational order decreases in the first 600 h after deposition, and then remains stable for at least several months.