Non-classical crystal growth of inorganic and organic materials

Investigation of the early stage morphologies of some organic and inorganic systems has established that their crystal growth does not always follow the classical route established 120 years ago. The classical theory assumes that a highly symmetric crystal develops from the nucleation and repeated attachment of atoms, molecules or ions to a single nucleus. In instances where surfactants or polymers were introduced the crystal growth was often found to follow a reversed crystal growth route. This non-classical growth route was initiated by organic molecules adsorbed onto the surface of the nanocrystallites in early growth stages. In the reversed route these nanocrystallites undergo aggregation into large disordered aggregates followed by surface crystallisation to create a thin highly crystalline and dense shell and finally an extension of the crystallisation from the surface to the core. Although systems following a non-classical crystal growth route have been known for many years their formation mechanisms have a much shorter history. Discovery of the reversed crystal growth route in several hollow, core shell and twin-crystal type morphologies not only assists in the designing of materials for industrial applications but also helps to understand the interactions between organic and inorganic components. This article highlights some recent research by featuring some organic and inorganic systems whose growth follows the reversed crystal growth route.