Solution growth of spherulitic rod and platelet calcium phosphate assemblies through polymer-assisted mesoscopic transformations.

Solution growth of apatite its precursors in the presence of urea commercial gelatin is found to lead, under appropriate conditions, to a rich spectrum of morphologies, among them high aspect ratio needles in uniform sturdy spherulitic assemblies resulting from a herein documented morphological 'Chrysalis Transformation'; the latter transformation involves the growth of parallel arrays of high aspect ratio needles within micron-scale tablets the formation of a radial needle arrangement upon disruption of tablet wrapping. A different level of gelatin leads to the formation of sturdy platelet-based spherulites through another morphological transformation. We also probe the role of four simple synthetic water-soluble polymers; we find that three of them (poly(vinyl alcohol), polyvinylpyrrolidone and polyacrylamide)) also affect substantially the assembly habits of apatite; the effect is similar to that of gelatin but the attained control is less perfect/complete. The case of poly(vinyl alcohol) provides, through variation of the degree of hydrolysis, insights as regards the chain architecture features that might favor morphological transformations. Morphological transformations of particle assemblies documented herein constitute novel ways of generating dense quasi-isotropic reinforcements with high aspect ratio ceramic particles; it becomes possible to tailor calcium phosphate phases at the structural level of crystal assembly.

Simple solution routes for targeted carbonate phases and intricate carbonate and silicate morphologies.

This work deals with the preparation of ceramic phases similar to those encountered in natural biocomposites through relatively fast and low-cost aqueous routes and various simple reactants and additives such as urea, commercial gelatin and hexamethyldiamine. In addition to the crystallographic (or amorphous) character of targeted phases (calcite, vaterite, aragonite, silica and silicates) particle morphology is also of interest and among others, we have obtained fractions of particles in the form of nanofibrilar calcite networks, calcium silicate doughnuts and Gordian knots, and diatom-like perforated silica cylinders.