Combining simultaneous reflectance and fluorescence imaging with SEM for conclusive identification of polycrystalline features of MFI membranes

Optical reflectance imaging of dye-saturated, c-oriented MFI membranes is employed for the first time as an in situ technique to conclusively identify the fluorescing features imaged simultaneously through fluorescence confocal optical microscopy (FCOM). For relatively thick (10-25 μm), well-oriented membranes, the reflectance image reveals the crystalline grains at the membrane surface. It provides low-resolution insight reminiscent of SEM, and augments FCOM techniques enabling direct correlation of the fluorescing regions of the membrane with the peripheries of the crystal grains (i.e., grain boundaries). Direct comparison of reflectance, fluorescence, and SEM images of an identical region of the membrane, rather than qualitative comparison of images from different membranes, conclusively confirms that molecular probes (dyes) of maximum diameter greater than the MFI pore dimensions access grain boundaries within the polycrystalline MFI membranes.