Assembled structures of nanocrystals in polymer/calcium carbonate thin-film composites formed by the cooperation of chitosan and poly(aspartate)

Assembled structures of calcium carbonate (CaCO3) nanocrystals have been examined for polymer/CaCO3 thin-film composites synthesized through a self-organization process inspired by biomineralization. For the crystallization of CaCO3, a thin-film matrix of chitosan has been used as a polymeric substrate. When the matrix is immersed into a supersaturated aqueous solution of CaCO3 containing 1.4 x 10(-3) wt % poly(aspartate) (PAsp), thin-film crystals of CaCO3 are formed spontaneously. Three kinds of disklike films have been observed under a polarizing optical microscope. Electron diffraction analyses of each film have revealed that one is aragonite, displaying radial orientation of the c axes, and the others are vaterite, exhibiting different orientations. Detailed observation by scanning electron microscopy has clarified that these films are assemblies of crystalline particles 10-20 nm in size. The thin-film composites have been obtained over a PAsp concentration range of 4.4 x 10(-4) to 1.0 X 10(-2) Wt %. Vaterite formation becomes dominant when the concentration of PAsp is increased. (c) 2006 Wiley Periodicals, Inc.