Nanoscale Morphology of Water in Silica Colloidal Crystals

We show a simple method to visualize the morphology of water adsorbed within the pore network of colloidal crystals made of submicrometer silica spheres. Water is replicated into silica by modified silicon tetrachloride hydrolysation under standard ambient conditions, making it visible to standard electronic microscopy and thus allowing one to discern the original water distribution. Different distribution patterns are identified depending on the water content, surface condition, and spheres arrangement. The dimension and shape of wetting layers (covering the submicrometer spheres) and capillary bridges (joining them) are measurable at the nanoscale. We finally use these findings to demonstrate proof-of-principle of fabrication of isolated and freestanding silica nanorings by using hydrophobic polymeric templates and selective etching.