On the Problem of Stability of Small Objects by the Example of Molecular Dynamics Models of Metal Nanoparticles and Nanosystems

After briefly discussing the problem of stability/instability of dispersed systems in colloid chemistry, including ideas and concepts dating back to P.A. Rehbinder, the following classification has been proposed for instabilities of individual (free) nanoparticles: (1) instability with respect to the spontaneous disintegration into individual molecules (atoms) or smaller nanoclusters; (2) instability of shape; (3) instability of the integral structure of nanoparticles; (4) instability of the mesoscopic structure; (5) instability of physicochemical characteristics of nanoparticles; and (6) instability with respect to an external environment, including chemical instability, e.g., instability to oxidation. The problems concerning the stability of isomers of metal nanoclusters and of bimetallic core-shell nanostructures are considered as examples. The theoretical concepts of stability and instability have been illustrated by our molecular dynamics data on isomers of Au nanoclusters and mutually inverse (alternative) bimetallic Co@Au and Au@Co core-shell nanostructures, where the first element (before symbol @) corresponds to the central region (core) of a particle, while the second one refers to its shell.