Surface roughness and chemical properties of porous inorganic films

Porous inorganic films of different materials and pore architecture: mesoporous gamma-alumina, mesoporous yttria stabilized zirconia (YSZ), macroporous YSZ and macroporous/microporous zeolite silicalite, were synthesized by the sol-gel spin-coating or dip-coating methods on silicon wafers of different surface roughness. Their surface chemical properties, pore and phase structure, and surface roughness were studied by various surface characterization methods. The pore sizes of these films are determined by their primary particle size. All the films studied are hydrophilic due to the presence of hydroxyl groups on the external crystallite surface, and their hydrophilicity increases in the order: macroporous YSZ < mesoporous YSZ < silicalite < gamma-alumina. The gamma-alumina films have highly smooth surfaces, while mesoporous YSZ, macroporous YSZ and silicalite films have similar surface roughness much rougher than gamma-alumina films. The surface roughness of these coated films does not depend on the coating method, surface roughness of the substrate, surface chemistry or pore structure of the films. It is more controlled by the shape and size of the primary particles and aggregates in the sol or suspension from which the films are obtained. (C) 2015 Elsevier B.V. All rights reserved.