Morphogenesis of shapes and surface patterns in mesoporous silica

The synthesis of inorganic materials with complex form, using surfactant assemblies as supramolecular templates, has ramifications in areas as diverse as large-molecule catalysis, the formation of semiconductor nanostructures, biomolecule separations, the development of medical implants and the morphogenesis of skeletal forms. Here we describe a procedure for the synthesis of hexagonal mesoporous silica that produces a remarkable array of shapes, surface patterns and channel plans. Our reaction conditions favour curved morphologies including toroidal, disk-like, spiral and spheroidal shapes. We use scanning electron microscopy to catalogue the basic topologies and surface patterns, and transmission electron microscopy to establish the relationship between morphology and the underlying mesostructure. Polarized optical microscopy enables us to identify a connection between optical anisotropy in these structures and the periodic porous mesostructure. We propose that the morphogenesis of these shapes and surface patterns can be rationalized in terms of the growth of a silicate liquid-crystal embryo with a hexagonal cross-section that, under different initial reaction conditions, is subject to increasing degrees of curvature.