Inorganic Crystallization Engineered by the Dynamic Adsorption of Linear and Particulate Polyelectrolytes

For most of natural hybrid materials, the shape of mineral crystals is controlled by natural polymers (e.g., proteins) to provide designated and unique physical properties and functions. Synthetic hybrid materials, which show comparable performance to the natural ones, require well-controlled crystal growth. In particular, the dynamic process including adsorption of the polymers on the crystal surface plays a significant role. We investigated CaSO4·0.5H2O crystallization in the presence of linear or particulate charged macromolecules, which can interact electrostatically with the crystals. Not only the static factors such as concentration and charge fraction but also the diffusion dynamics of the charged macromolecules were found crucial to involve the complete inhibition of growth and the subsequent shape transition of the crystals. This leads to the elucidation of semiquantitative relationships between dynamic factors such as the diffusion of macromolecules and the rate of crystal growth to the growth inhibition. The diffusion-limited adsorption model was coherent with the experimental evidence, i.e., the effects of molecular weight of linear polyelectrolyte and the size of charged spherical micelles. This fundamental understanding of dynamic adsorption during the crystal growth would provide the basis for the kinetic control of polymer/inorganic hybrid assembly in both biological and engineering contexts.