Crystallization of Vaterite Nanowires by the Cooperative Interaction of Tailor-Made Nucleation Surfaces and Polyelectrolytes

The concepts of template-induced crystallization on self-assembled monolayers (SAMs) and the use of polymer additives are combined into a new strategy, where, through the cooperative interaction of a SAM matrix involved in the nucleation process, poly(acrylic acid), a dissolved polyelectrolyte, and the dissolved ions, hierarchically ordered mineral structures are formed. The adsorption of poly(acrylic acid) to the SAM is monitored using a quartz microbalance. Transmission electron microscopy measurements on samples that are taken from polyacrylate solution in short intervals after the start of the reaction reveals that nanometer-sized particles pre-formed in solution are being attached to the polymer template. These CaCO₃ nanoparticles are still amorphous 20 min after the start of the mineralization process; the transformation from the amorphous to the crystalline phase takes place within the first 60 min of the reaction. The morphologies of the crystalline products exhibit characteristic differences from those that are obtained in crystallization experiments on self-assembled monolayers without the polyelectrolyte. This model of cooperative formation of vaterite nanowires represents an alternative to current models of structure formation, where two-phase systems (e.g., microemulsions or foams) act as a structure-directing interface, or the mineralization process is caused by the diffusion of a hydrolyzable component from a non-aqueous into an aqueous phase.