Striking World of Nanostructures

Abstract

Two classes of nanostructures produced by comminution of macroscopic bodied, by aggregation of free molecules or ions are characterized. Interfacial phenomena in the nanostructures are described. The definition of surface tension as an excess surface stress is given and the condition of mechanical equilibrium at an arbitrarily curved interface is formulated. The influence of interfacial phenomena on the dependence of properties of nanoparticles on their size is discussed. Thermodynamic equations are derived describing first-order and second-order phase transitions in nanoparticles. Polymorphous transformations of solid phases in the comminution process are analyzed. A chemical approach to description of solid nanoparticles, based on introduction of the chemical potential of a supramolecule and the chemical affinity of a process, is characterized. A theory of polymorphous transformations and solution of solid nanoparticles is formulated on the ground of the chemical approach. In the section devoted to aggregative systems, unusual properties of micelles and vesicles of surfactants are described: the dualism of their liquid-like and solid-like behavior and the absence of their macroscopic analog; the universal (with respect to various properties of solution) abruptness of the transition to formation of nanostructures as the critical micelle concentration is attained; the qualitative difference in the thermodynamic properties of aggregates corresponding to a maximum and a minimum in the curve of equilibrium size distribution of aggregates; and the decrease in the concentration of a surface-active ion in a micellar solution at adding its mother substance, a strong electrolyte, to the solution. An approach to specifying thermodynamic relationships for description of the lamellar (onion-like) structure of micelles is proposed.