Effect of stabilizing binder and dispersion media on spin-on zeolite thin films

The influence of the dispersion media and types of binding agent on the hydrophilic properties of silica MFI-type films is evaluated. As dispersants ethanol, butanol and hexanol are used to stabilize the purified MFI nanocrystals in coating suspensions. Three types of binders, including non-purified silica MFI, pre-hydrolyzed tetraethoxysilane, and colloidal alumina were mixed with MFI nanocrystals stabilized in different dispersants in various ratios, and deposited on silicon wafers by spin-on process. The main physicochemical properties including homogeneity, thickness, and surface roughness of the films were determined by atomic force microscopy, scanning electron microscopy and ellipsometry. Additionally, the crystalline structure and degree of disorientation of the MFI crystallites in the films were characterized by grazing X-ray incident diffraction. Besides, the degree of hydrophobicity of films is evaluated by comparing the ellipsometry data with contact angle measurements. It has been found that the colloidal alumina binder introduced hydrophilic centers, high disordering, and low density resulting in higher hydrophilicity, while the as-synthesized silica MFI and pre-hydrolyzed tetraethoxysilane binders formed dense, more stable and hydrophobic films.