Formation of Thin Calcium Carbonate Films on Chitosan Biopolymer Substrates

Abstract

Crystallization of two-dimensional spherulitic calcium carbonate films was performed on planar films of chitosan in the presence of poly(acrylic acid) (PAA). PAA, electrostatically bound to the chitosan substrate, increased the local concentration of calcium at the surface, thereby promoting CaCO3 crystallization there. Simultaneously, interaction between PAA and calcium ions in the surrounding solution suppressed bulk crystallization. Increasing the PAA concentration at fixed pH increased the surface supersaturation of calcium ions leading to larger spherulites. Saturation of the surface with PAA at 0.004% led to a maximum in the nucleation rate at this concentration. Above a certain PAA concentration, a regime existed at which the surface was completely covered. Above even higher PAA concentrations no crystallization occurred, since the bulk PAA sequestered all of the calcium ions in solution previously available for surface crystallization. As the pH increased, PAA became more charged and therefore int...