In this Research Equipment project, an advanced laser fluorescence apparatus will be 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 recovery after photobleaching (FRAP) where the film is bleached in a periodic pattern. This improved FRAP technique will avoid many of the problems associated with the radiotracer technique for measuring surface diffusion. This new experimental technique also will permit one to extend the study surface diffusion to interfacial systems previously inaccessible to study by the radiotracer method. In addition, one will be able to separate between flow and diffusional transport processes occurring in monomolecular films. The periodic pattern increases the spatial resolution relative to the conventional single spot FRAP technique, resulting in more accurate diffusion constant determinations. This apparatus will be 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/fluid interfaces. The laser fluorescence apparatus also will be used in other research projects including monolayer structure, L-B films, bilayers, and solid/liquid interfaces.
