Growth of bubbles in liquid.

BACKGROUND: Evolution of a gas injected in a liquid is analyzed using the example of the behavior of oxygen molecules in water in which bubbles of gas molecules grow slowly by attachment of gas molecules to bubbles, the bubbles then associate and finally flow up to the liquid-gas interface and pass into the gas phase. RESULTS: Two methods are considered for gas injection in a liquid, insertion of individual molecules and injection of small gas bubbles via gas penetration through a porous material. The behavior of oxygen bubbles in water and growth of those bubbles is analyzed. Subsequently, these grown bubbles float up and disappear, or reach the water boundary as a result of turbulent motion of the liquid. CONCLUSIONS: It is shown that measurement of the size distribution function of micron-size bubbles in various regions of the water container allows one to establish the flow current lines on the basis of the theory of bubble growth. Graphical abstract:Schematic diagram of energies of molecules in the gas phase, in bubbles and bound to solvent.

Where macro meets micro.

Reconciling or somehow linking the macroscopic and microscopic approaches to chemical and physical processes has been a challenge unaddressed for many years. One approach, presented here, treats the issue by examining individual phenomena well described by a macro approach that fails when applied to small systems. The key to the approach is determining the approximate system size below which the breakdown of the macro description is observable. The most developed example is the failure of the Gibbs phase rule for sufficiently small atomic clusters. Other examples, such as the onset, at sufficient size, of the insulator-to-metal transition, are discussed, as are some still more challenging phenomena.

Entropy behavior in cluster melting.

We analyze the configurational excitation of a cluster for both a microcanonical and a canonical ensemble of atoms and apply this analysis to the Lennard-Jones cluster of 13 atoms. Dividing the cluster excitations into configurational and thermal classes, we evaluate the anharmonicity coefficient of atomic vibrations and the entropy jump as a function of temperature on the basis of computer simulations of the Lennard-Jones 13-atom cluster as a canonical and a microcanonical ensemble of atoms. This analysis shows the role of anharmonicity of atomic vibrations and exhibits the importance of the temperature dependence of the entropy jump in the range of phase coexistence for cluster thermodynamics.

Flow of nanosize cluster-containing plasma in a magnetron discharge.

A magnetron source of silver clusters captured by an argon flow with the quadrupole mass filter is used for the analysis of charged clusters after an orifice of the magnetron chamber, and the size distribution function follows from the analysis of clusters deposited on a silicon substrate by an atomic force microscope. Cluster charge near an orifice results from attachment of ions of a secondary plasma that is a tail of a magnetron plasma, and the cluster charge is mostly positive. The character of passage of a buffer gas flow with metal clusters through an orifice is studied both theoretically and experimentally. Assuming the cone shape of the drift chamber near the orifice, we analyze drift of charged clusters in a buffer gas flow towards the orifice if the electric field inside the drift chamber is created by charged rings on the cone surface. Under experimental conditions, when an equilibrium between the buffer gas flow and cluster flux is violated, a typical voltage of rings and parameters of corona discharge for cluster charging are estimated if the electric field does not allow for clusters to reach walls of the drift chamber. The number density of clusters near the orifice is estimated that increases both due to violation of an equilibrium for the cluster flux inside the buffer gas flow and owing to focusing of the cluster by the electric field that is created by electrodes located near walls and due to diffusion motion of clusters. Processes of cluster charging in the magnetron chamber are analyzed.