Porous Ceramics, Ceramic/Polymer, and Metal-Doped Ceramic/Polymer Nanocomposites via Freeze Casting of Photo-Curable Colloidal Fluids

摘要

A novel and general process for the fabrication of porous ceramics and metal/ceramic/polymer nanocomposites by freeze-photocuring-casting (FPC) is presented. The homogenous fluid containing water, curable monomers, and colloidal particles is frozen, and the phase separated microstructure is fixed by photo-initiated polymerization. At the relatively high resin/particle ratio explored here, the structure is sufficiently strong to withstand the capillary forces during ambient drying; however, it is capable of transforming to macroscopic ceramics such as Al_2O_3 and SiO_2 by conventional debinding and sintering. The use of FPC fluids enables producing porous macroscopic shapes such as microspheres, films, and multilayer coatings having an ordered, interconnected pore network and pore sizes down to the low sub-micrometer range. The pore structure is found to be dependent on the radius of curvature of the macroscopic structure. Ag-TiO_2/polyacrylate porous nanocomposites are produced by co-shaping of FPC containing sterically stable colloids, soluble metal salts, and monomers. Ag nanoparticles form in situ by reduction of Ag~+ ions on the TiO_2 surface. This triggers the photo-polymerization of the resin without the need of a photoinitiator. It is found that if the cured layers in a multilayer stack are frozen before the newly deposited layer, the ice crystal structure formed is linked via epitaxial growth.