The Hierarchical Architecture of Nacre and its Mimetic Materials

The nacreous layer has been found to be composed of a three-level hierarchical architecture consisting of aragonite nano-building blocks. The nanometric crystals in submicrometric oriented platy units were bridged and covered with organic molecules. Nanostorage, an additional nanoscopic function leading to the incorporation of versatile organic dye molecules, resided in the aragonite/ biopolymer composites. Nacre-mimetic architectures in terms of the oriented assembly of nanocrystals with nanostorage were successfully produced through the crystal growth of alkali-earth carbonates in aqueous systems containing soluble polymeric species, such as poly(acrylic acid) (PAA) and silicate anions. A hierarchy similar to the nacreous layer could be formed by an appropriate combination of potassium sulfate and PAA. The nanometric and submicrometric stepwise growth of inorganic crystals accompanied with specific adsorption of soluble polymeric molecules is associated with the formation of a hierarchical architecture consisting of bridged nanocrystals.