CRYSTAL DESIGN OF CALCIUM-CARBONATE MICROPARTICLES USING DOUBLE-HYDROPHILIC BLOCK-COPOLYMERS

Small block copolymers, consisting of a hydrophilic poly(ethylene glyc ol) block and a second hydrophilic moiety which strongly interacts wit h alkaline earth ions, were employed to template the precipitation of calcium carbonate from aqueous solation, Depending on the type of poly meric functionalization pattern used, it was possible to grow two of t he three different crystal modifications of CaCO3 (vaterite and calcit e) di under similar conditions. Vaterite could be. successfully stabil ized for more than 1 year by the polymer under conditions where it wou ld normally transform into calcite within 80 h. Also the crystal size and shape respond to the polymeric template; for example, it was possi ble to grow monodisperse spherical particles with a diameter of ca. 2 mu m or hollow spheres both consisting of aggregated nanocrystallites. The effect of different functional groups and of variable block lengt h on the size? shape, and morphology of CaCO3 is discussed. it must be emphasized that these particles sediment, but are stabilized and prot ected by a dense layer of double-hydrophilic block copolymers, which e nables direct use as pigments and fillers or in ceramic processing.