Substrate-directed formation of calcium carbonate fibres

This article describes the formation of fibres of calcium carbonate on a range of substrates in the presence of a polyacid diblock copolymer, and it is demonstrated that the morphologies and structures of the fibres can be controlled by judicious selection of both the substrate and the reaction conditions. While fibres precipitated on single crystals of calcite and aragonite proved to be single crystals of calcite, those formed on glass and mica were amorphous and frequently displayed remarkable helical morphologies. Investigation of the fibre growth mechanism(s) suggests that all formed via the self-assembly of polymer-stabilised precursor units. Particles forming the calcite single-crystal fibres were elongated calcite crystallites, and fibre formation was interpreted in terms of an oriented assembly process, where anisotropy in the precursor unit morphology and surface distribution of copolymer chains promoted one-dimensional assembly. In contrast, the particles that formed amorphous fibres were spherical and amorphous, with fibre formation being attributed to polarisation of these copolymer-rich particles. This work therefore demonstrates that directional aggregation processes can be applied to both amorphous and crystalline units, opening up the possibility of using block copolymers to control the morphologies of a very wide range of materials.