Monolithic pure silica gels with hierarchical macro-mesoporous structure have been synthesized via a spontaneous sol−gel process from silicon alkoxide using a structure-directing agent and a micelle-swelling agent. A monolithic body with well-defined co-continuous macropores is a result of concurrent phase separation and sol−gel transition induced by the polymerization reaction, whereas the mesopores are templated by the cooperative self-assembly of inorganic species, a structure-directing agent, and a micelle-swelling agent. These bimodal pore systems are formed spontaneously in a closed condition at a constant temperature. The following removal of surfactants by heat-treatment gives silica gels with hierarchical and fully accessible pores in discrete size ranges of micrometers and nanometers. The highly ordered 2D-hexagonal arrays of mesopores have been confirmed by X-ray diffraction measurements and FE-SEM observations. Furthermore, by further additions of the micelle-swelling agent, the mesostructural transition from well-ordered 2D-hexagonal arrays to mesostructured cellular foams (MCF) has been induced accompanied by minor modifications of the micrometer-range structure.

Monolithic ethane−silica gels with well-defined co-continuous macropores and highly ordered mesopores have been synthesized via a spontaneous route from silicon alkoxide with the aid of a structure-directing agent. While the macropores are formed by the concurrent phase separation and sol−gel transition induced by the polymerization reaction, the mesopores are templated by the self-organization of the structure-directing agent. Starting from a homogeneous mixture of the starting components, all the structure formation processes take place spontaneously in closed conditions at a constant temperature. Subsequent evaporation drying and heat treatment result in gels with hierarchical and fully accessible pores in discrete size ranges of micrometer and nanometer. While the local alignment of the mesopores is confirmed by FE-SEM observation, the long-range mesoscale order over the whole sample is evidenced by X-ray diffraction measurements. With the addition of a micelle-swelling agent, the mesostructural transition from 2D-hexagonal order to mesostructured cellular foam, MCF, has been observed without disturbing the macroporous framework structure.

By combining the micellar templating in nanometer-scale with the polymerization-induced phase separation in micrometer-scale, we can synthesize monolithic silica or silsesquioxane gel materials with hierarchical well-defined macropores and shape-controlled mesopores. Depending on the mechanism of enhancing micellar-templating of siloxane oligomers, macroframeworks containing long-range-ordered cylindrical mesopores with different degrees of order have been produced. Alkylene-bridged silicon alkoxides can also be prepared into similarly hierarchical porous structures with broadened variations in framework morphology. These examples demonstrate the versatility of using phase-separation in micellartemplated gelling systems to obtain well-defined macroporous structures.