Control of mode of crystal networking during monolayer assembly of microcrystals on water

A series of hydrocarbon (HC)-coated cubic zeolite microcrystals (1.7 microm) was prepared. The HCs were n-octyl, n-dodecyl, methyl n-undecanoate, n-octadecyl, and n-heptadecafluorodecyl. The measured water contact angles (theta) of the corresponding HC-coated glass plates were 64, 77, 82, 102, and 105 degrees, respectively, indicating that the hydrophobicity of the surface-tethered hydrophobic chain (HC) increased in the above order. The HC-coated zeolite microcrystals readily formed closely packed monolayers at the air-water interface through interdigitation of surface-tethered HCs, and on glass plates after transferring onto glass plates by dip coating. Interestingly, while the mode of networking was face-to-face (FTF) contacting with n-octyl or n-dodecyl (theta < or =77 degrees) as HC, it changed to edge-to-edge (ETE) contacting mode with n-octadecyl or n-heptadecafluorodecyl (theta > or = 102 degrees) as HC. With methyl n-undecanoate (theta = 82 degrees) as HC, both modes appeared in the monolayers, with about equal populations. The resulting monolayers of cubic zeolite microcrystals with their three-fold axes oriented perpendicular to substrates would be useful for application of the zeolite monolayers for advanced materials.