Morphology-preserving transformation of minerals mediated by a temperature-responsive polymer membrane: Calcite to hydroxyapatite

Assemblies of nanocrystals with complex morphologies have attracted great scientific interest, but controlling the formation of these self-assembled structures has proved to be difficult. Here, we present a novel transformation reaction for transforming single crystals of minerals into assemblies of nanocrystals of substances with lower solubility while preserving the gross overall morphology. This study focuses on the transformation of rhombohedral calcite crystals to assemblies of hydroxyapatite (HAP) nanocrystals using poly(N-isopropylacrylamide)-block-poly(acrylic-acid) (PNIPAM-b-PAAc) to control the transformation process. This yielded particle assemblies of HAP nanoparticles grossly preserving the original rhombohedral calcite morphology.