Ostwald ripening of confined nanoparticles: chemomechanical coupling in nanopores

Abstract

Ostwald ripening is a major source of deactivation of functional nanomaterials. It consists in the growth of large nanoparticles at the expense of smaller ones via the formation and decomposition of intermediate chemical species. In most materials of practical interest nanoparticles are dispersed in porous supports with which they interact mechanically. We analyze the consequences of this chemo-mechanical coupling on both kinetic and equilibrium aspects of Ostwald ripening. We show that the long-term stability of a collection of confined nanoparticles depends on nucleation-like events, whereby few particles break through the pore walls early in the process and later grow at the expense of all other particles. This notably explains why the stability of confined nanoparticles depends critically on their initial size distribution; it also provides an explanation for the occasional observation of bimodal particle size distributions in aged materials.