Colloidal Assembly and Functionalization of Pore Channels in Polymer Foils

The deposition of ceramic colloidal particles into the pores of polymeric ion track membranes was studied. By means of a low-temperature sol-gel process, aqueous dispersions of ceramic nanoparticles can adhere to virtually any surface of a porous polymer foil (substrate) including the interior walls of the pores without adversely affecting the flexibility or ease of handling of the starting material. The coating method consists in depositing of a TiO₂-photocatalyst onto the substrate by providing either a SiO₂ or Ag specific layer or both between the photocatalyst and the substrate. Silica and metallic silver act as both binder and barrier against deterioration due to the photocatalytic action derived from TiO₂. On the other hand, the incorporation of such nanoparticles inside the pores provides active centres on which gas exchange coupled to photo-catalytic reactions can occur. Because of their small pore size, porous substrates can be very useful in a high purity filter application, for food package, gas-separation- and ion-exchange membranes. The structure and function of these ceramic-polymer composites were conceived and engineered taking ostrich eggshell as natural model. This bionic approach is based on the concept of immobilizing solid particles on a porous surface using polymer groups as tether.