In situ atomic force microscopy study on the crystallization of calcium carbonate modulated by poly(vinyl alcohol)s

The effect of polyvinyl alcohol) (PVA) on the crystallization of calcium carbonate is reported. Crystallization was initiated by flowing a supersaturated solution over a single crystal of calcite, and in situ atomic force microscopy (AFM) was utilized to observe the crystal growth. When no additives were in the supersaturated solution, typical step growth at the screw dislocation hillocks of calcite proceeded. When polyethylene oxide), poly(N-vinyl pyrrolidone), and poly(N-isopropyl acrylamide) were added to the solution, a similar behavior was observed. However, with PVA, dramatic changes occurred in the crystal growth. PVA initially induced step roughening, followed by step bunching, which led to macrostep formation. More importantly, PVA promoted two-dimensional (2D) nucleation and growth, which extensively affected the entire crystallization region. The change in growth mode, from step-flow initiating from dislocations to 2D island formation, originates from the PVA adsorption. The adsorbed PVA inhibits the advance of calcite steps and induces 2D island formation, together leading to a new surface morphology. The extensive 2D island formation with a macromolecular additive, but without a preorganized organic matrix, seems to be a technically attractive strategy to generate assembled microcrystals with occluded macromolecules, a structure well-known in biomineralization.