Abstract
We studied new mesoporous materials with original properties and obtained from self-assembled chitin-silica nano-composites. Our novel synthesis allows the controlled colloidal assembly of a-chitin nanorods (bundles of elongated chitin monocrystals) and siloxane oligomers. Calcination of nanocomposites results in mesoporous silica materials. Their pore volume fraction fPOR (0-0.52) is strongly correlated to the initial chitin content. Using N2 sorption and TEM data, we identify and characterize primary and secondary textural units related to the imprints of chitin monocrystals (2.5 nm wide) and nanorods (20-30 nm wide) respectively. Primary textural units are preserved over a wide fPOR range (linear relationship between pore volume and specific surface area). The coating of monocrystals by siloxane oligomers leads to a siloxane network of fractal nature as deduced from complementary SAXS data. Beyond a critical value fPOR 0 estimated near 0.2, the coating is partial, and the porosity becomes more open and connected. At larger scales, the arrangements of secondary textural units result in complex textures and long-range ordering, showing similarities with textural features found in natural materials. We discuss the competition between entropy-driven transitions typical of anisotropic particles and kinetic arrest due to colloidal gelation and inorganic condensation. Finally, a schematic model for texture formation is given.