Bicontinuous porosity in ceramics utilizing polymer spinodal phase separation

This paper demonstrates how the combination of inorganic and organic polymers can be used to form bicontinuous porosity in ceramics with pore sizes larger than 5 μm. Spinodal phase separation of pseudo-binary polymer mixtures allows to form larger bicontinuous pore structures than spinodal phase separation of inorganic glasses. Addition of salts allows even more complex compositions of ceramics and glasses to be formed. Here, bioactive glasses are presented that were produced via sol-gel processing of a pseudo-binary mixture of an inorganic and an organic polymer. Due to the addition of an organic polymer to the gelling sol and the spinodal phase separation at a specific equilibrium temperature, both an inorganic polymer ceramic phase and organic polymer-rich phase are formed. The evaporation of the solvent and the burnout of the organic polymer produce a microstructure of interconnected and nearly uniform porosity, which can be controlled by several processing parameters. The dependency of pore size and connectivity is best predicted by polymer phase separation rather than glass melt separation. Results suggest that polymer spinodal phase separation could be useful for the manufacture of a variety of porous ceramics.