(617b) Closed Packed, Oriented MOF Thin Films through Solution Shearing

Metal organic frameworks (MOFs) are a class of nanoporous crystalline materials that are composed of metal clusters connected through organic ligands. Their ultrahigh porosity and internal surface area, tunability of the organic and inorganic components, and possibility of the incorporation of various functional groups make them suitable candidates in a variety of applications such as gas storage and separation, catalysis, sensing, etc. Whereas the majority of MOFs have been produced and tested in the form of powder, the deposition of MOF crystals or their in-situ formation on an appropriately functionalized substrate to make thin films has gained significant attention. Such films could then be used as catalytic or separation membranes, sensors, electronic devices, etc. MOF film fabrication through the deposition of solvothermally synthesized crystals, however, frequently results in rough, randomly oriented, low density, or poorly adhered coatings of undesired size/morphology crystals, which could be inefficient in practical applications. On the other hand, some of the state-of-the-art techniques for the controlled deposition of MOFs on substrates such as the Layer-by-Layer (LbL) method typically suffer from slow kinetics. Solution shearing is a novel thin film formation and crystal deposition technique, in which the precursor solution or crystal suspension is sandwiched between a shearing blade and a substrate. Crystals form in-situ or deposit from the suspension over the appropriately-heated substrate while the blade moves at an adjusted speed. This method has already shown its potential in providing fine control on film density, thickness, and alignment in the field of organic electronics and can readily be employed for large-scale fabrications. Using solution shearing and characterization techniques such as grazing incidence X-ray diffraction (GIXD), we have managed to make highly aligned dense films of MOF crystals and investigated the crystalline characteristics and shearing parameters that control the quality of final products.