An advanced laser fluorescence apparatus is developed to determine the surface or translational diffusion coefficients of fluorescent-labeled probes in monomolecular films at air/water and oil/water interfaces. This improved apparatus is based on a simple Moire technique for measuring surface diffusion using fluorescence photobleaching recovery (FPR) where the film is bleached in a periodic pattern. This new experimental technique also permits an extended study of surface diffusion to interfacial systems previously inaccessible to study by the radiotracer method. In addition, it is possible to separate between flow and diffusional transport processes occurring in monomolecular films. This apparatus is being used to continue previous work on surface diffusion in monomolecular films, in particular, to determine reliable values of the surface diffusion coefficient and its surface concentration and temperature dependence within various monolayer states in order to elucidate the nature of two-dimensional mass transfer at fluid interfaces. The laser fluorescence apparatus also is used in other research projects.
